u pb dating of monazite and its application to geological problems monazite is an underutilized mineral in u pb geochronological studies of crustal rocks it occurs as an accessory mineral in a wide variety of rocks including granite pegmatite felsic volcanic a

geochronology and tectonic implications of magmatism and metamorphism southern kootenay arc and neighbouring regions southeastern british columbia part i jurassic to mid cretaceous k ar dates and u pb zircon dates define three periods of igneous activity in the southern kootenay arc 1 emplacement of late synkinematic to post kinematic granodioritic plutons in mid jurassic time 170 165 ma accompanying amphibolite facies regional metamorphism 2 emplacement of post kinematic granitic plutons in mid cretaceous time 100 ma and 3 emplacement of small bodies of syenite in eocene time 50 ma in the western part of the area micas from mid jurassic plutons that yield the oldest k ar dates 158 166 ma also yield plateau shaped 40ar 39ar age spectra age spectra for biotites younger than these but older than 125 ma reflect thermal overprinting in southeastern british columbia the kootenay arc marks the transition from the north american rocks of the cordilleran miogeocline to the tectonic collage of allochthonous terranes that have been accreted to it deformation metamorphism and plutonism recorded in rocks of the southern kootenay arc commenced in mid jurassic time as a co

tectonic and magmatic significance of strontium isotopic variations in cenozoic volcanic rocks from the western united states more than 800 sr isotopic analyses of cenozoic volcanic rocks have been compiled for the western united states and parts of northern mexico these data indicate significant variations in 87 sr 86 sr that reflect changes in tectonic evolution and differences in magmatic style that is origin and evolution of igneous rocks for this region as a function of time and space late cenozic volcanic rocks mainly basalts represent magmatism associated with essentially extensional tectonism over much of the western united states in general 87 sr 86 sr ratios in these basalts are lower than in early cenozic rocks but display systematic variations in space for the most part isotopic compositions of these rocks are considered representative of their respective mantle source regions if this is the case the mantle source regions are isotopically heterogeneous and seemingly reflect a compositional provinciality that is correlated with the age of crustal rocks in this region specifically ancient subcontinental lithospheric mantle may be characterized by higher 87 sr 86 sr ratios than the mantle beneath younger crustal terranes early cenozoic volcanic rocks mainly intermediate to silicic calc alkalic in composition formed while the western united states was undergoing regional compression associated with subduction along the pacific margin sr isotopic ratios in these rocks are generally higher and more variable than in the younger extensional regime magmas and they are highest in areas of the eastern cordillera where old sialic crust is present the isotopic data are in accord with the involvement of crustal material in the genesis and evolution of these calc alkalic magmas crustal contamination of primitive subduction related magmas and crustal anatexis due to advective heat transfer associated with their ascent are considered as dominant factors in early cenozic magmatism variables in the subduction process itself in the nature and age of crust and mantle wall rocks and in the amount and provenance of subducted sediments likely contribute to the diversity of subduction related magmatism

textural chemical and isotopic insights into the nature and behaviour of metamorphic monazite monazite is a mineral of choice for dating metamorphism in amphibolite and granulite grade metapelites however there exist a number of difficulties that complicate the interpretation of monazite geochronological data and prevent its application to many geological problems the two main obstacles addressed in this contribution are firstly the minor but significant e g 1 30 ma dispersal in duplicate isotope dilution thermal ionisation mass spectrometry id tims u pb age data commonly recorded from a single rock and secondly the difficulty of attaching monazite age data to pressure and temperature information through a multidisciplinary approach utilising tims and laser ablation multicollector inductively coupled plasma mass spectrometry la mc icpms isotope data quantitative and qualitative emp chemical analyses of monazite and textural studies we assess the significance of pb loss older components and continuous and episodic monazite growth in the generation of dispersed age data three samples from the canadian cordillera and one sample from the himalaya of pakistan are examined each sample exhibits an age dispersion of between 1 and 12 ma for single crystal and multi grain tims u pb monazite age determinations consideration of the closure temperature for pb diffusion in monazite and the metamorphic temperatures experienced by these samples suggests diffusive pb loss did not play a significant part in generating this age dispersal the la mc icpms study indicates that an older component 100 ma older than the tims ages contributed to the age dispersal in three of the four samples in all the samples however chemical analyses identified that the majority of monazites examined exhibited significant intra crystalline zoning in y content the la mc icpms analysis of one sample that was constrained to zones of distinct y content indicates that these zones are of distinct age we suggest that monazite grown before the appearance of garnet and during garnet breakdown is relatively rich in y whereas monazite grown after garnet is relatively poor in y a combination of these chemical data with textural observations suggests that once monazite had entered the mineral assemblage it grew or recrystallised episodically throughout the prograde and retrograde paths of the metamorphic event this behaviour contributes to and in one of the samples controls the observed age dispersal this recognition allows the generation of pressure temperature time points by combining textural and chemical information of monazite with in situ age determinations and pressure temperature information from garnet thus the episodic growth of compositionally distinct monazite throughout a metamorphic event provides the geochronologist with a very valuable chronological tool

sediment plumes as a proxy for local ice sheet runoff in kangerlussuaq fjord west greenland meltwater runoff is an important component of the mass balance of the greenland ice sheet gris and contributes to eustatic sea level rise in situ measurements of river runoff at the 325 outlets are nonexistent due to logistical difficulties we develop a novel methodology using satellite observations of sediment plumes as a proxy for the onset duration and volume of meltwater runoff from a basin of the gris sediment plumes integrate numerous poorly constrained processes including meltwater refreezing and supra and englacial water storage and are formed by meltwater that exits the gris and enters the ocean plume characteristics are measured in moderate resolution imaging spectroradiometer modis band 1 250m satellite imagery during the 2001 08 melt seasons plume formation and cessation in kangerlussuaq fjord west greenland are positively correlated r 2 0 88 n 5 p 0 05 r 2 0 93 n 5 p 0 05 with ablation onset and cessation at the kangerlussuaq transect automatic weather station s5 490ma s l 6km from the ice margin plume length is positively correlated r 2 0 52 n 35 p 0 05 with observed 4day mean watson river discharge throughout the 2007 and 2008 melt seasons plume length is used to infer instantaneous and annual cumulative watson river discharge between 2001 and 2008 reconstructed cumulative discharge values overestimate observed cumulative discharge values for 2007 and 2008 by 15 and 29 respectively

greenland ice sheet motion coupled with daily melting in late summer 1 we use ground based and satellite observations to detect large diurnal and longer period variations in the flow of the greenland ice sheet gris during late summer that are strongly coupled with changes in its surface hydrology the diurnal signals are associated with periodic changes in surface melting and the longer period signals are associated with the episodic drainage of supra glacial lakes ice velocity doubles around 2 hours after peak daily melting and returns approximately to wintertime levels around 12 hours afterwards demonstrating an intimate link between the surface and basal hydrology during late summer the ice sheet accelerates by 35 per positive degree day of melting the observed link between surface melting and enhanced flow is typical of alpine glaciers which may provide an appropriate analogue for the evolution of the gris in a warming climate

mesozoic cenozoic deformation in the canadian cordillera the record of a continental bulldozer abstract a possible mesozoic cenozoic trajectory for the north american craton is outlined from latitude changes of the craton derived from a revised apparent polar wander path and from westward movement of the craton based on the assumption that africa has been the least mobile continent geographically since the latest paleozoic during each of five time intervals that span 220 million years the craton trajectory had a different vector each vector appears to be reflected in the canadian cordillera by the dominant style and orientation of structures formed during that interval for much of the past 220 million years the meridionally oriented western margin of the pangea laurasia north america plate has been the site of arc magmatism where weak arc back arc lithosphere sandwiched between strong ocean floor and craton lithospheres at times coupled across convergent or transform plate boundaries focused and recorded strain when the craton apparently moved due westward between 180 160 ma and 120 60 ma the dominant structures formed then record orogen normal compression and were accompanied by orogeny structures formed during the earlier episode are mainly in the eastern and interior cordillera and their formation shortly followed or coincided with accretion of most terranes to the craton margin in the later episode compressional structures span the entire cordillera which emerged as a tectonic and physiographic entity before and between these intervals when the craton apparently moved mostly northwestward mainly geological and paleomagnetic considerations indicate some terranes moved southward sinistrally relative to the craton after 60 ma southwestward movement of the craton was concurrent with large northward dextral strike slip faults that disrupted the newly established ancestral cordillera the coincidence between the age of structures that record dominant orogen normal compression at times when the craton apparently moved due westward and orogen parallel displacements when the craton had either northward or southward components of motion suggests the craton acting as a continental bulldozer was the primary driver of cordilleran deformation and orogenesis

middle jurassic exhumation along the western flank of the selkirk fan structure thermobarometric and thermochronometric constraints from the illecillewaet synclinorium southeastern british columbia new thermobarometric and thermochronometric data from the illecillewaet synclinorium a broad regional southwest verging structure in the western flank of the selkirk fan structure indicate that accretion of the intermontane superterrane resulted in deep burial 20 25 km of the outer margin of ancestral north america and that subsequent southwest verging folding and thrusting were accompanied by rapid exhumation southwest verging folding of lower paleozoic rocks in the illecillewaet synclinorium was initiated during regional peak metamorphic conditions at 6 7 kbar crystallization of late synkinematic granitoid plutons that intrude the illecillewaet synclinorium also occurred at pressures of 6 7 kbar however equilibration of the contact aureoles of the plutons occurred at 3 3 5 kbar during the latter stages of the southwest verging deformation evidently a decompression on the order of 3 kbar occurred concurrently with southwest verging folding and thrusting in the illecillewaet synclinorium thermochronometric analyses further indicate that plutonic rocks from the illecillewaet synclinorium cooled rapidly between times of crystallization and times of ar closure in biotite regional relationships indicate that the accretion of the intermontane superterrane to the edge of the north american margin in southeastern british columbia occurred between 187 and 173 ma toarcian bajocian subsequent southwest verging deformation occurred approximately between 173 and 168 ma bajocian bathonian thus the removal of at least 10 km of rocks from above the illecillewaet synclinorium inferred from thermobarometric data occurred approximately between 173 and 168 ma rapid denudation of the selkirk fan structure was probably the result of synorogenic extension or extensional collapse contemporaneous with the development of southwest verging structures at deeper levels of the orogen the data presented here indicate that all significant deformation and most of the exhumation along the western flank of the selkirk fan structure were complete by late middle jurassic time after the middle jurassic the selkirk fan structure must have been transported passively northeastward along the basal decollement of the cordilleran foreland thrust and fold belt together with the intermontane superterrane as the fold and thrust belt tectonically overrode the margin of the north american craton

an electron microprobe study of the u th pb systematics of metamorphosed monazite the role of pb diffusion versus overgrowth and recrystallization abstract an electron microprobe emp was used to obtain u th pb chemical ages from monazite that underwent an amphibolite facies metamorphic overprint in the monashee complex southern canadian cordillera u pb isotope dilution dating of single grains yielded discordant ages that plot in linear arrays on a concordia diagram upper intercepts of the arrays indicate primary growth in the proterozoic and cretaceous and lower intercepts are coeval with a tertiary metamorphic event the microprobe s high spatial resolution 2 m and ability to quickly differentiate between domains with greatly contrasting u th and pb concentrations made it the ideal tool for investigating the cause of the u pb isotopic discordance the microprobe dating shows that proterozoic monazite lies directly adjacent to generally small

seasonal speedup of the greenland ice sheet linked to routing of surface water we use interferometric synthetic aperture radar observations recorded in a land terminating sector of western greenland to characterise the ice sheet surface hydrology and to quantify spatial variations in the seasonality of ice sheet flow our data reveal a non uniform pattern of late summer ice speedup that in places extends over 100 km inland we show that the degree of late summer speedup is positively correlated with modelled runoff within the 10 glacier catchments of our survey and that the pattern of late summer speedup follows that of water routed at the ice sheet surface in late summer ice within the largest catchment flows on average 48 faster than during winter whereas changes in smaller catchments are less pronounced our observations show that the routing of seasonal runoff at the ice sheet surface plays an important role in shaping the magnitude and extent of seasonal ice sheet speedup

pressure temperature and evolution of fluid compositions of al 2 sio 5 bearing rocks mica creek b c in light of fluid inclusion data and mineral equilibria metamorphosed pelitic rocks from mica creek british columbia contain sillimanite kyanite with minor fibrolite and andalusite bearing quartz pods mineral equilibria were used to infer peak p t conditions and fluid compositions in equilibrium with the solid phases fluid inclusions in three schist samples appear to be good indicators of conditions affecting those rocks during and after peak metamorphic conditions in samples from two localities fluid inclusions from schist and quartz rich segregations have densities appropriate to the peak metamorphic conditions the observed compositions for these fluids low salinity with 12 mole dissolved co2 agree with calculated text x text h text 2 text o values of 0 84 to 0 85 based upon paragonite quartz albite al2sio5 equilibria the fluids unmixed as the schists were uplifted and cooled fluid inclusions trapped during this stage outline a solvus in the co2 h2o nacl system a later influx of fluids containing ch4 and n2 accompanied formation of andalusite bearing plagioclaserich segregations the restricted association of andalusite bearing pods and low density fluids suggest a localized but pervasive fluid influx during uplift preservation of high density fluid inclusions during uplift and erosion coupled with evidence for unmixing of h2o and co2 rich fluids on the solvus provide constraints on the p t uplift path

orogenic pulses in the alberta rocky mountains radiometric dating of major faults and comparison with the regional tectono stratigraphic record radiometric ages from regionally distributed thrust fault gouge show that the eastward propagation of the southern rocky mountain fold and thrust belt in canada occurred in four orogenic pulses that correlate with tectonic events of the cordilleran interior and with depositional patterns in the adjacent foreland in the main ranges the pyramid 163 0 ma simpson pass 161 7 ma and johnson creek 145 7 ma thrusts were related to the initiation of thin skinned deformation from jurassic terrane accretion and were partly contemporaneous with development of the first clastic wedge in the foreland basin in the front ranges the emplacement of the greenock thrust 103 1 ma and broadview snake indian thrust 99 2 ma was contemporaneous with development of cenomanian deltaic deposits in the immediate foreland three thrusts in the front ranges rocky pass 74 8 ma sulfur mountain 75 6 ma and clearwater 74 2 ma thrusts define a campanian phase of tectonic loading that led to the last major transgression in the southern portion of the alberta foreland along the eastern margin of the front ranges the mcconnell thrust 54 0 ma together with the muskeg 52 4 ma brule 53 9 ma and nikanassin 52 1 ma thrusts in the foothills recorded the last phase of regional contraction the late jurassic mid cretaceous late cretaceous and early eocene deformation pulses are separated by relatively long periods 40 m y 20 m y and 10 m y of tectonic quiescence these spatially and temporally restricted fault motion pulses contrast with gradual forward fault propagation while regional eastward progression of deformation is preserved

acceleration of the contribution of the greenland and antarctic ice sheets to sea level rise 1 ice sheet mass balance estimates have improved substantially in recent years using a variety of techniques over different time periods and at various levels of spatial detail considerable disparity remains between these estimates due to the inherent uncertainties of each method the lack of detailed comparison between independent estimates and the effect of temporal modulations in ice sheet surface mass balance here we present a consistent record of mass balance for the greenland and antarctic ice sheets over the past two decades validated by the comparison of two independent techniques over the last 8 years one differencing perimeter loss from net accumulation and one using a dense time series of time variable gravity we find excellent agreement between the two techniques for absolute mass loss and acceleration of mass loss in 2006 the greenland and antarctic ice sheets experienced a combined mass loss of 475 158 gt yr equivalent to 1 3 0 4 mm yr sea level rise notably the acceleration in ice sheet loss over the last 18 years was 21 9 1 gt yr2 for greenland and 14 5 2 gt yr2 for antarctica for a combined total of 36 3 2 gt yr2 this acceleration is 3 times larger than for mountain glaciers and ice caps 12 6 gt yr2 if this trend continues ice sheets will be the dominant contributor to sea level rise in the 21st century

sediment plume response to surface melting and supraglacial lake drainages on the greenland ice sheet increased mass losses from the greenland ice sheet and inferred contributions to sea level rise have heightened the need for hydrologic observations of meltwater exiting the ice sheet we explore whether temporal variations in ice sheet surface hydrology can be linked to the development of a downstream sediment plume in kangerlussuaq fjord by comparing 1 plume area and suspended sediment concentration from moderate resolution imaging spectroradiometer modis imagery and field data 2 ice sheet melt extent from special sensor microwave imager ssm i passive microwave data and 3 supraglacial lake drainage events from modis results confirm that the origin of the sediment plume is meltwater release from the ice sheet interannual variations in plume area reflect interannual variations in surface melting plumes appear almost immediately with seasonal surface melt onset provided the estuary is free of landfast sea ice a seasonal hysteresis between melt extent and plume area suggests late season exhaustion in sediment supply analysis of plume sensitivity to supraglacial events is less conclusive with 69 of melt pulses and 38 of lake drainage events triggering an increase in plume area we conclude that remote sensing of sediment plume behavior offers a novel tool for detecting the presence timing and interannual variability of meltwater release from the ice sheet

deformations tardi grenvilliennes dans la ceinture parautochtone province de grenville centrale contraintes geochronologiques par couplage de methodes u pb de haute resolution spatiale et de haute precision dans la ceinture parautochtone de la province de grenville centrale reservoir manicouagan la datation des structures revele que l orogene grenvillien a oblitere les fabriques anterieures ainsi les structures d1 et d2 indiquent un cisaillement inverse a vergence nord avec respectivement des lineations sse et sso les structures d3 indiquent un cisaillement oblique normal a vergence oso une strategie innovatrice combinant la geochronologie u pb sur zircon par ablation laser la icp ms et par abrasion chimique par dilution isotopique ca id tims contraint l ge de ces deformations les surcroissances internes et externes des grains de zircon d un leucosome syn d2 indiquant deux periodes de croissance sont interpretees respectivement comme les ges de d1 et d2 le groupe 1 donne un ge 206pb 207pb de 1008 18 ma la icp ms et un ge concordia de 1002 2 ma ca id tims le groupe 2 donne un ge 206pb 207pb de 995 21 ma la icp ms et un ge concordia de 986 4 ma ca id tims une pegmatite t

observed runoff jokulhlaups and suspended sediment load from the greenland ice sheet at kangerlussuaq west greenland 2007 and 2008 this study fills the gap in hydrologic measurements of runoff exiting a part of the greenland ice sheet gris the kangerlussuaq drainage area west greenland the observations are of value for obtaining knowledge about the terrestrial freshwater and sediment output from part of the gris and the strip of land between the gris and the ocean in the context of varying ice sheet surface melt and influx entering the ocean high resolution stage discharge and suspended sediment load show a decrease in runoff of approx 25 and in sediment load of approx 40 from 2007 to 2008 in response to a decrease in the summer accumulated number of positive degree days during the 2007 and 2008 runoff season joekulhlaups are observed at kangerlussuaq drained from an ice dammed lake at the margin of the gris

seasonal speedup along the western flank of the greenland ice sheet it has been widely hypothesized that a warmer climate in greenland would increase the volume of lubricating surface meltwater reaching the ice bedrock interface accelerating ice flow and increasing mass loss we have assembled a data set that provides a synoptic scale view spanning ice sheet to outlet glacier flow with which to evaluate this hypothesis on the ice sheet these data reveal summer speedups 50 to 100 consistent with but somewhat larger than earlier observations the relative speedup of outlet glaciers however is far smaller 15 furthermore the dominant seasonal influence on jakobshavn isbrae s flow is the calving front s annual advance and retreat with other effects producing outlet glacier speedups an order of magnitude larger seasonal melt s influence on ice flow is likely confined to those regions dominated by ice sheet flow

early cretaceous kyanite sillimanite metamorphism and paleocene sillimanite overprint near mount cheadle southeastern british columbia geometry geochronology and metamorphic implications mapping of isograds related to regional amphibolite facies metamorphism constrains a three dimensional model of isogradic surfaces near mount cheadle in the northern shuswap metamorphic complex lat 52 20 n long 119 05 w kyanite and sillimanite coexist in a lens shaped zone bounded by the kyanite out and sillimanite in isogradic surfaces that is 50 km long up to 10 km thick and up to 20 km wide textural equilibrium simple regular geometry of isogradic surfaces and simple mineral assemblages suggest that metamorphism occurred at p t conditions near those of the kyanite sillimanite equilibrium curve reconstruction of isotherms in the kyanite sillimanite zone suggests that the metamorphic field gradient was about 14 c km 1 a 5 km thick staurolite free kyanite zone adjacent to the sillimanite in isograd suggests a pressure range of about 1 5 kbar 1 kbar 100 mpa for bathozone 5 of d m carmichael regional metamorphism was early cretaceous monazite u pb geochronology with quenching in th

automated remote sensing of sediment plumes for identification of runoff from the greenland ice sheet the viability of employing sediment plumes emanating from outlets along the western margin of the greenland ice sheet as indicators of runoff is assessed an automated sediment plume quantification system based on daily 250 m moderate resolution imaging spectroradiometer modis band 1 reflectance imagery is developed coherent plumes are identified using spectral thresholds and polygon tracing validation employs imagery quality control procedures and manual verification of plume areas outlets at land terminating margins with wide and straight fjord geometries deliver the most accurate and consistent results plume area observations are also possible at marine terminating margins with relatively static fronts and low proximal sea ice concentrations variability in plume area is examined with reference to special satellite microwave imager ssm i derived daily melt extent at the hydrologic catchment scale at annual timescales plume areas tend to co vary with surface melt extent indicating that more mass is lost by runoff during years of extensive melting some synchronicity in plume areas from different catchments is apparent at seasonal and daily timescales plumes from individual outlets primarily relate to catchment specific melting

recent changes on greenland outlet glaciers aircraft laser altimeter surveys during the 1990s showed near coastal parts of the greenland ice sheet to be thinning despite slow thickening at higher elevations the ice sheet lost mass to the ocean many outlet glaciers thinned more rapidly than could be explained by increased melting during the recent warmer summers indicating dynamic imbalance between glacier velocity and upstream snow accumulation results from more recent surveys presented here show that thinning rates have increased in most coastal regions for almost half of the surveys these increases might have resulted from increases in summer melting but rapid thinning on others is indicative of dynamic changes that increased with time in particular thinning rates on the three fastest glaciers increased to tens of m a 1 after 2000 and other observations show an approximate doubling in their velocities the deep beds of these glaciers appear to have a strong influence on rates of grounding line retreat and thickness change with periods of glacier acceleration and rapid thinning initiated by flotation and break up of lightly grounded glacier snouts or break up of floating ice tongues near simultaneous thinning of these widely separated glaciers suggests that warming of deeper ocean waters might be a common cause nearby glaciers without deep beds are thinning far more slowly suggesting that basal lubrication as a result of increased surface melting has only a marginal impact on greenland outlet glacier acceleration

alpine subglacial hydrology abstract the size and shape of subglacial flow pathways exert a strong influence over the pressure and speed at which meltwaters are routed through glaciers these characteristics in turn influence glacier sliding velocity and the quantity and quality of bulk meltwaters discharging from glaciers in this paper we summarise four empirical research approaches that have been developed to improve our understanding of the subglacial hydrology of predominantly temperate based alpine glaciers investigations of bulk meltwater discharge and chemistry tracer studies proglacial bedrock investigations and borehole investigations as a result of linking these studies to conceptual or numerical models three arborescent and four non arborescent or distributed subglacial drainage configurations are described these drainage networks may be neither spatially nor temporally persistent but may compete with and replace each other on a seasonal basis a qualitative model of the temporal and spatial evolution of a typical alpine subglacial drainage system is advanced on the basis of research conducted at haut glacier d arolla switzerland

retention of greenland runoff by refreezing implications for projected future sea level change melting produced at the surface of subfreezing permeable firn does not freely percolate but instead refreezes near its point of origin raising the firn temperature and decreasing the pore space if sufficient meltwater is introduced the firn will warm to 0 c and subsequent water will fill the remaining pore space without freezing only after the residual water content of the firn is exceeded will water flow through the firn and possibly escape as runoff this process prevents summer melt on high arctic glaciers and ice caps from escaping in its entirety and it must be accounted for in modeling glacier runoff on the basis of surface energy balance a model is presented here which describes in a simple way the transient process of infiltration refreezing and runoff in a future warming climate the model is applied to greenland for which predictions of runoff induced sea level rise that do not consider the refreezing process could be as much as 5 0 cm too high over 150 years

changes in the velocity structure of the greenland ice sheet using satellite radar interferometry observations of greenland we detected widespread glacier acceleration below 66 north between 1996 and 2000 which rapidly expanded to 70 north in 2005 accelerated ice discharge in the west and particularly in the east doubled the ice sheet mass deficit in the last decade from 90 to 220 cubic kilometers per year as more glaciers accelerate farther north the contribution of greenland to sea level rise will continue to increase

hydrologic drainage of the greenland ice sheet a simple hydrologic drainage network for the greenland ice sheet is modelled from available digital elevation models dems of bedrock and surface topography and assumptions of hydrostatic water pressure uniform hydraulic conductivity and no conduit flow within the ice sheet as such it is a first order model best suited for broad scale hydrological assessment results identify 293 distinct hydrologic basins 185 117 000 km2 together with their realized wet and unrealized dry drainage patterns intersection with 1991 2000 polar mm5 pmm5 mesoscale climate model hindcasts of meltwater runoff suggest that these basins route varying amounts of water to the ice edge ranging from 0 to 16 km3 annually and totalling 242 km3 year for the entire ice sheet regionally speaking average annual volumetric meltwater production km3 year is highest in southwest and lowest in northeast greenland with greater hydrologic activity in western regions than in eastern regions for a given latitude the extent to which meltwater truly reaches the ice margin as modelled is difficult to test however the simulated flow outlet locations show qualitative agreement with the locations of 460 observed meltwater outlets proglacial lakes streams and rivers and sediment plumes into fjords mapped continuously along the ice sheet perimeter on average about 36 of the modelled drainage network was activated i e received water over the 1991 2000 study period remaining areas barring dynamic changes to ice surface topography would presumably activate if surface melt penetrates deeper into the ice sheet interior both new datasets are freely available for scientific use at the national snow and ice data center ftp sidads colorado edu pub datasets parca nsidc 0372 hydrologic outlets ftp sidads colorado edu pub datasets parca nsidc 0371 hydrologic sub basins copyright 2009 john wiley sons ltd

spatially distributed runoff at the grounding line of a large greenlandic tidewater glacier inferred from plume modelling understanding the drivers of recent change at greenlandic tidewater glaciers is of great importance if we are to predict how these glaciers will respond to climatic warming a poorly constrained component of tidewater glacier processes is the near terminus subglacial hydrology here we present a novel method for constraining near terminus subglacial hydrology with application to marine terminating kangiata nunata sermia in south west greenland by simulating proglacial plume dynamics using buoyant plume theory and a general circulation model we assess the critical subglacial discharge if delivered through a single compact channel required to generate a plume that reaches the fjord surface we then compare catchment runoff to a time series of plume visibility acquired from a time lapse camera we identify extended periods throughout the 2009 melt season where catchment runoff significantly exceeds the discharge required for a plume to reach the fjord surface yet we observe no plume we attribute these observations to spatial spreading of runoff across the grounding line persistent distributed drainage near the terminus would lead to more spatially homogeneous submarine melting and may promote more rapid basal sliding during warmer summers potentially providing a mechanism independent of ocean forcing for increases in atmospheric temperature to drive tidewater glacier acceleration

multiphase formation of superimposed ice during a mass balance year at a maritime high arctic glacier meteorological and snow temperature data from midtre lovenbreen spitsbergen svalbard indicate two distinct annual phases of rapid snowpack warming and superimposed ice formation in 1998 99 short periods of positive air temperatures in early winter lasting up to 36 hours and often coinciding with rainfall caused rapid glacier wide melting percolating water froze to form superimposed ice on the lower half of the glacier and wetted refrozen snow and ice lenses at higher altitudes the second period of superimposed ice formation commenced in may june 1999 and continued for 5 weeks at low altitudes and throughout the summer at high altitudes these observations at midtre lovenbreen are typical of spitsbergen glaciers and reflect the unique climatology of the region they contrast with those from glaciers in more continental climatic settings where superimposed ice formation is confined to a single period during summer there are significant implications for glacier mass balance with superimposed ice locally comprising up to 20 of winter balances and accounting for 16 25 of the annual accumulation since projected climatic warming is greatest during the winter months in arctic regions superimposed ice may become an increasingly important component of the winter and potentially the net balance of spitsbergen glaciers

acceleration of greenland ice mass loss in spring 2004 in 2001 the intergovernmental panel on climate change projected the contribution to sea level rise from the greenland ice sheet to be between 0 02 and 0 09 m from 1990 to 2100 ref 1 however recent work has suggested that the ice sheet responds more quickly to climate perturbations than previously thought particularly near the coast here we use a satellite gravity survey by the gravity recovery and climate experiment grace conducted from april 2002 to april 2006 to provide an independent estimate of the contribution of greenland ice mass loss to sea level change we detect an ice mass loss of 248 36 km3 yr 1 equivalent to a global sea level rise of 0 5 0 1 mm yr 1 the rate of ice loss increased by 250 per cent between the periods april 2002 to april 2004 and may 2004 to april 2006 almost entirely due to accelerated rates of ice loss in southern greenland the rate of mass loss in north greenland was almost constant continued monitoring will be needed to identify any future changes in the rate of ice loss in greenland

electron beam analytical instruments and the determination of modes spatial variations of minerals and textural features of rocks in polished section point counts based on x ray intensities collected with an automated electron beam analytical instrument can be used to estimate the accurate modes required by modern physical chemical modelling of rock forming processes in addition the spatial distributions of mineral species and mineral compositions can be extracted from the coordinates of the point counting grid statistical tests of whether the mineral and porosity distributions are uniform can be performed by comparing the results from subareas of the polished section the separate and composite contributions of the mineral phases to the texture and structure of the rock can be visually represented with mineral distribution maps qualitative differences in grain size can be recognized because the nonzero finite electron beam diameter can detect grain boundaries spots on the minerals are identified by comparing the ranking of x ray intensities with the ranking of intensities on a set of standards for example this method identified more than 88 of the spots on the surface of a polished section of an alkali olivine basalt a small additional number of spots approximately 1 were identified because their spectra were dominated by the x ray intensities of two characteristic elements this method was particularly efficient in identifying phases with a small grain size and simple chemistry e g apatite the modal amounts of an alkali olivine basalt obtained with a microprobe are within approximately one standard deviation of the results obtained by point counting the same areas of the polished section under reflected and transmitted light if the minerals are major constituents and occur only in the groundmass accessory and phenocryst phases agree to within approximately three standard deviations

seasonal speedup of a greenland marine terminating outlet glacier forced by surface melt induced changes in subglacial hydrology we present subdaily ice flow measurements at four gps sites between 36 and 72 km from the margin of a marine terminating greenland outlet glacier spanning the 2009 melt season our data show that 35 km from the margin seasonal and shorter time scale ice flow variations are controlled by surface melt induced changes in subglacial hydrology following the onset of melting at each site ice motion increased above background for up to 2 months with resultant up glacier migration of both the onset and peak of acceleration later in our survey ice flow at all sites decreased to below background multiple 1 to 15 day speedups increased ice motion by up to 40 above background these events were typically accompanied by uplift and coincided with enhanced surface melt or lake drainage our results indicate that the subglacial drainage system evolved through the season with efficient drainage extending to at least 48 km inland during the melt season while we can explain our observations with reference to evolution of the glacier drainage system the net effect of the summer speed variations on annual motion is small 1 this in part is because the speedups are compensated for by slowdowns beneath background associated with the establishment of an efficient subglacial drainage system in addition the speedups are less pronounced in comparison to land terminating systems our results reveal similarities between the inland ice flow response of greenland marine and land terminating outlet glaciers

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

subglacial hydrology at rink isbrae west greenland inferred from sediment plume appearance marine terminating outlet glaciers discharge most of the greenland ice sheet s mass through frontal ablation and meltwater runoff while calving can be estimated by in situ and remote sensing observations submarine melting and subglacial meltwater transport are more challenging to quantify here we investigate the subglacial hydrology of rink isbrae a fast flowing west greenland tidewater glacier using time lapse photography modeled runoff estimates and daily satellite imagery from 2007 to 2011 we find that sediment plumes appear episodically at four distinct locations across the terminus and last between 2 h and 17 d this suggests short term variability in discharge and the existence of persistent pathways the seasonal onset of sediment plumes occurs before supraglacial lake drainages shortly after the onset of runoff and only after the wintertime ice melange has begun disintegrating plumes were also visible after the cessation of runoff 23 5 d which is indicative of subglacial storage the lack of either a seasonal velocity change or a correspondence between meltwater availability and plume occurrence suggests that the subglacial system persists in a state of inefficient drainage subglacial hydrology at tidewater glaciers is of critical importance in understanding dynamics at the ice front

tectonic links between the clachnacudainn terrane and selkirk allochthon southern omineca belt canadian cordillera the clachnacudainn terrane in the southern omineca belt is interpreted as an integral part of the overlying selkirk allochthon based on stratigraphic igneous metamorphic and deformational links across the boundary between them the standfast creek fault an inverted homocline correlated with lower paleozoic lardeau group metasedimentary and metavolcanic rocks is continuous across the fault the fault is transected by post ductile strain granitoids of inferred and known mid cretaceous age such as the 104 1 ma albert stock as well as by peak regional metamorphic m2 isograds and contact metamorphic m3 isograds associated with the albert stock three phases of regional ductile deformation including major west verging second phase f2 folds are correlated across the fault these tectonic links strongly suggest that the clachnacudainn terrane and selkirk allochthon share a similar tectonic history and thereby require that the standfast creek fault has minor tectonic significance compared with other faults in the southern omineca belt m2 and coeval f2 folds are interpreted as resulting from middle jurassic tectonism documented elsewhere in the selkirk allochthon the main aspect that differentiates the clachnacudainn terrane from the rest of the selkirk allochthon east of the monashee complex is the clachnacudainn igneous complex which dominates the northern part of the terrane and is the product of prolonged igneous activity

investigations of meltwater refreezing and density variations in the snowpack and firn within the percolation zone of the greenland ice sheet the mass balance of polythermal ice masses is critically dependent on the proportion of surface generated meltwater that subsequently refreezes in the snowpack and firn in order to quantify this effect and to characterize its spatial variability we measured near surface 26 resulting in a 32 increase in net accumulation this seasonal densification increased at lower elevations rising to 47 10km closer to the ice sheet margin at 1860 m a s l density depth profiles from nine sites within 1 km 2 at similar to 1945ma s l reveal complex stratigraphies that change over short spatial scales and seasonally we conclude that estimates of massbalance change cannot be calculated solely from observed changes in surface elevation but that near surface densification must also be considered however predicting spatial and temporal variations in densification may not be straightforward further the development of complex firn density profiles both masks discernible annual layers in the near surface firn and ice stratigraphy and is likely to introduce error into radar derived estimates of surface elevation

surface melt induced acceleration of greenland ice sheet flow ice flow at a location in the equilibrium zone of the west central greenland ice sheet accelerates above the midwinter average rate during periods of summer melting the near coincidence of the ice acceleration with the duration of surface melting followed by deceleration after the melting ceases indicates that glacial sliding is enhanced by rapid migration of surface meltwater to the ice bedrock interface interannual variations in the ice acceleration are correlated with variations in the intensity of the surface melting with larger increases accompanying higher amounts of summer melting the indicated coupling between surface melting and ice sheet flow provides a mechanism for rapid large scale dynamic responses of ice sheets to climate warming

the treatment of meltwater retention in mass balance parameterisations of the greenland ice sheet retention of melt water runoff by percolation and or refreezing in the snowpack cannot be neglected when studying the surface mass balance of the greenlandice sheet in this paper we make a detailed comparison of several treatments proposed in the literature to account for this process in large scale mass balanceparameterizations the melt on the greenland ice sheet is calculated with a revised degree day model using updated datasets of surface elevation and precipitationrate on a 5 km grid crucial model parameters are recalibrated by comparing mass balance characteristics with available observations on a regional basis wediscuss the role of meltwater retention in the light of the overall mass balance of the greenland ice sheet and its sensitivity to climatic change and displaypatterns of effective retention fractions for the various methods as a main conclusion it appears that overall results are quite similar for the various models butthat meltwater retention has a large spatial variation not described by the simple treatments using the most comprehensive retention model the sensitivity of therunoff is found to be 0 35 mm deg c of sea level change per year we also present a new map of the different zones facies that characterize the accumulationarea of the greenland ice sheet that is useful for interpreting field data and calibrating satellite observations

plagioclase clinopyroxene garnet quartz equilibria and the geobarometry and geothermometry of garnet amphibolites from mica creek british columbia metabasites form a small but significant volume of the upper precambrian horsethief creek group near mica creek british columbia sillimanite zone assemblages in metabasites are hornblende plagioclase ilmenite quartz garnet clinopyroxene sphene calcite the incoming of garnet clinopyroxene in metabasites very nearly coincides with the kyanite sillimanite isograd fe mg distributions between coexisting garnet and clinopyroxene suggest a temperature range of 650 705 c ellis and green calibration the higher temperature estimates disagree with the upper thermal stability limits of muscovite plagioclase quartz sillimanite from adjacent pelitic rocks pressure estimates based upon clinopyroxene garnet plagioclase quartz equilibria are 5 6 0 3 and 7 2 0 3 kbar 560 30 and 720 30 mpa respectively using two different calibrations of this geobarometer these estimates bracket the pressure estimated from garnet plagioclase al2sio5 equilibria in pelitic rocks

modeling the impact of glacial runoff on fjord circulation and submarine melt rate using a new subgrid scale parameterization for glacial plumes the injection at depth of ice sheet runoff into fjords may be an important control on the frontal melt rate of tidewater glaciers here we develop a new parameterization for ice marginal plumes within the massachusetts institute of technology general circulation model mitgcm allowing three dimensional simulation of large 500 km2 glacial fjords on annual or longer time scales we find that for an idealized fjord without shelf driven circulation subglacial runoff produces a thin strong and warm down fjord current in the upper part of the water column balanced by a thick and slow up fjord current at greater depth although submarine melt rates increase with runoff due to higher melt rates where the plume is in contact with the ice front we find that annual submarine melt rate across the ice front is relatively insensitive to variability in annual runoff better knowledge of the spatial distribution of runoff controls on melt rate in those areas not directly in contact with plumes and feedback mechanisms linking submarine melting and iceberg calving are necessary to more fully understand the sensitivity of glacier mass balance to runoff driven fjord circulation

supraglacial forcing of subglacial drainage in the ablation zone of the greenland ice sheet 1 we measure hydrological parameters in meltwater draining from an outlet glacier in west greenland to investigate seasonal changes in the structure and behaviour of the hydrological system of a large catchment in the greenland ice sheet gris our data reveal seasonal upglacier expansion and increase in hydraulic efficiency of the subglacial drainage system across a catchment 600 km2 to distances 50 km from the ice sheet margin this expansion occurs episodically in response to the drainage of surface meltwaters into a hitherto inefficient subglacial drainage system as new input locations become active progressively further upglacier this system is similar to alpine glaciers these observations provide the first synopsis of seasonal hydrological behaviour in the ablation zone of the gris

a reappraisal of the tectonic significance of early tertiary low angle shear zones exposed in the vernon map area 82 l shuswap metamorphic complex southeastern canadian cordillera detailed geological mapping across the shuswap metamorphic complex between latitudes 50 00 n and 50 45 n reveals that superstructure forms a semicontinuous carapace across the complex with minimal evidence of internal thinning near the western margin of the complex superstructure and infrastructure are juxtaposed across low angle 2 km thick ductile shear zones spatially associated with paleocene to early eocene syn kinematic granitic rocks the shear zones which yield upper plate to the west shear sense indicators are interpreted as the northern extension of the okanagan valley fault farther east near the north south axis of the complex superstructure and infrastructure are separated by an attenuated metamorphic section but evidence of noncoaxial strain is lacking discrete detachments were not found steeply dipping normal faults cut low angle shear zones and do not merge with them at depth middle eocene volcanic and sedimentary rocks rest unconformably on metamorphic basement the continuit

modeling glacial meltwater plume dynamics and sedimentation in high latitude fjords 1 a model sedplume has been developed to simulate marine sediment deposited by glacial meltwater plumes emerging from tidewater glaciers turbid meltwater emerging from beneath a glacier into a fjord rises as a buoyant forced plume due to density contrasts with the ambient fjord water sedplume assumes that meltwater discharge flows at a constant rate for long enough periods that the plume reaches a steady state entrainment of ambient fluid into the turbulent plume is assumed to occur at a rate proportional to the local velocity of the plume plume motion is considered in two dimensions one horizontal dimension perpendicular to the glacier front and the vertical dimension an integral model is formulated for the conservation equations of volume momentum buoyancy and sediment flux along the path of a turbulent plume injected into stably stratified ambient fluid sedimentation occurs from the plume when the radial component of the sediment fall velocity exceeds the entrainment velocity when the plume reaches the surface it is treated as a radially spreading surface gravity current for which exact solutions exist for the sediment deposition rate flocculation of silt and clay particles is modeled using empirical measurements of particle settling velocities in fjords to adjust the settling velocity of fine grained sediments sedplume has been applied to mcbride inlet alaska a temperate glaciated fjord where the majority of sedimentation originates from meltwater sources sedplume produces rates and patterns of sedimentation in good agreement with observations with calculated peak ice proximal annual sedimentation rates of approximately 22 m yr 1

stratigraphy and deformational history of the scrip nappe monashee mountains british columbia the scrip nappe a large recumbent anticline that occupies the northern selkirk and northern monashee mountains has an inverted lower limb some 50 km in length across strike and comprises stratigraphic divisions of the hadrynian horsethief creek group which can be traced southward with decreasing metamorphic grade through the selkirk mountains to the northern purcell mountains the scrip nappe has a southwesterly vergence and it formed that way during the first folding phase of the mesozoic columbian orogeny metamorphism no greater than biotite zone accompanied that first deformation the nappe was subsequently refolded into tight northeast verging folds metamorphism rose to upper amphibolite facies late in the second deformation phase after the metamorphic climax northeast verging buckle folds and associated crenulation cleavage formed locally during a third folding episode the entire nappe complex was then carried northeastward on the purcell thrust over the folds and thrusts of the western r

snowmelt on the greenland ice sheet as derived from passive microwave satellite data abstract the melt extent of the snow on the greenland ice sheet is of considerable importance to the ice sheet s mass and energy balance as well as arctic and global climates by comparing passive microwave satellite data to field observations variations in melt extent have been detected by establishing melt thresholds in the cross polarized gradient ratio xpgr the xpgr defined as the normalized difference between the 19 ghz horizontal channel and the 37 ghz vertical channel of the special sensor microwave imager ssm i exploits the different effects of snow wetness on different frequencies and polarizations and establishes a distinct melt signal using this xpgr melt signal seasonal and interannual variations in snowmelt extent of the ice sheet are studied the melt is found to be most extensive on the western side of the ice sheet and peaks in late july moreover there is a notable increasing trend in melt area between the years 1979 and 1991 of 4 4 per year which came to an abrupt halt in 1

three dimensional grain fabric measurements using high resolution x ray computed tomography abstract high resolution x ray computed tomography hrxct provides detailed imagery of the interiors of rocks up to hand sample size non destructively and in three dimensions new tools described here allow these data to be used for analysis of grain fabrics two separate sets of measurement techniques have been developed the first concentrates on quantifying individual crystals phenocrysts porphyroblasts or other discrete objects or void spaces within a sample quantifiable properties include location size shape orientation and contact relationships with adjacent objects the second set of techniques performs a more general fabric analysis on any distinguishable component in a sample a fabric tensor can be computed based on a number of metrics including the star volume distribution svd star length distribution sld and mean intercept length mil methods the fabric tensors provide principal component directions and magnitudes which in turn provide a measure of degree of anisotropy and shape indices because the svd and sld measure only the material of interest whereas the mil is also influenced by spatial distribution results can be divergent for sparse phases also introduced is a three dimensional rose diagram that can be viewed interactively and inspected to reveal further details about non orthogonal directional components these techniques are demonstrated through analysis of a garnet kyanite schist from mica dam british columbia

spatial and temporal melt variability at helheim glacier east greenland and its effect on ice dynamics this is the publisher s version also available electronically from http onlinelibrary wiley com

u pb geochronological constraints on the timing of episodic regional metamorphism and rapid high t exhumation of the grand forks complex british columbia abstract the grand forks complex gfc is a fault bounded metamorphic core complex in the southern omineca belt of british columbia canada it experienced prograde metamorphism ranging from upper amphibolite to granulite facies conditions during the mesozoic to early tertiary compressional stage of the cordilleran orogeny peak metamorphism was followed by multi stage exhumation in the early eocene this study provides u pb monazite and zircon constraints on the timing of metamorphic episodes in the gfc and subsequent high t amphibolite facies decompression in the early eocene monazite la icp ms ages from metapelitic gneisses record episodic metamorphism from the late jurassic to paleocene with peak metamorphism occurring between 59 and 50 ma peak metamorphism was followed by rapid near isothermal decompression of the gfc between 52 and 50 ma and leucosome crystallization at 50 ma thermodynamic modeling of metapelites in the system mnnckfmashpyce predicts that monazite was not stable at peak metamorphic conditions consistent with the dominant population of 59 ma ages representing growth along the prograde path most likely at subsolidus conditions growth of widespread high y monazite rims 50 ma is predicted along suprasolidus decompression and cooling paths zircon shrimp ages from igneous bodies in the gfc and hanging wall of the bounding kettle river fault krf suggest ductile deformation related to high t decompression of the gfc was ongoing at 51 ma but had ceased by 50 ma truncated by post kinematic granitoids this high t deformation predates subsequent greenschist facies extension on the overlying krf a pre krf hanging wall ductile shear zone is constrained to 59 51 ma it deforms 59 ma ladybird suite leucogranites and may be related to high t exhumation of the core complex rapid 100 c ma cooling rates are required to accommodate high t amphibolite facies exhumation of the gfc at 52 50 ma followed by low t greenschist facies exhumation at 49 ma

seasonal variability in the dynamics of marine terminating outlet glaciers in greenland recent studies indicate that the dynamics of fast flowing marine terminating outlet glaciers of the greenland ice sheet may be sensitive to climate and ocean forcing on sub annual timescales observations of seasonal behavior of these glaciers at such high temporal resolution however are currently few here we present observations of front position flow speed near surface air temperature and ocean conditions for six large marine terminating glaciers in the uummannaq region of west greenland to investigate controls on short term glacier dynamics as proposed by other studies we find that seasonal front advance and retreat correlates with the formation and disappearance of an ice melange our data suggest that high sea surface temperature anomalously low sea ice concentration and reduced melange formation in early 2003 have triggered multi year retreat of several glaciers in the study area which is consistent with other regions in greenland of the stable glaciers only rink isbrae exhibits a seasonal speed variation that correlates with variations in front position with the others undergoing mid summer deceleration that indicates the effects of subglacial meltwater discharge and drainage system evolution drainage of supraglacial lakes and water filled crevasses results in substantial decreases in speed 40 60 on fast flowing glaciers our results demonstrate that attempts to model ice sheet evolution must take into account short timescale flow dynamics resulting from drainage events and oceanographic conditions

response of glacier basal motion to transient water storage the speed of a glacier is affected most by sudden jumps in the water supply to the glacier but it goes back to previous levels if high water inputs are sustained because the glacier s plumbing system adjusts

glaciology greenland s glacial basics sliding of the greenland ice sheet is affected by the production of surface meltwater a new theory shows that whether the result is a long term speed up or slow down of ice motion depends on the variability in melt input see letter p 803 recent observations in greenland have led to the notion that surface meltwater supply to the ice sheet bed lubricates ice flow suggesting that climate warming could lead to runaway glacial acceleration christian schoof uses a physically based model that captures drainage channelization under the ice to challenge this view the model shows that increased melt supply leads to channelization and a drop in water pressure this causes ice flow to slow down rather than speed up however this effect can be overcome if melt supply is variable over short timescales when temporary pressure spikes can lead to accelerated flow the positive melt dynamic thinning feedback is therefore still viable but is heavily dependent on daily temperature variations and rain events that are largely ignored in current ice sheet models

40ar 39ar dates on hornblende muscovite and biotite from the mica creek area british columbia regional metamorphic and tectonic implications a metamorphic high the selkirk monashee cariboo complex smc is a 200 km 60 km area cored by k feldspar sillimanite rocks in the mica creek area there appear to be no discontinuities in metamorphic isograds structural trends or the late precambrian stratigraphic units u pb dates suggested that the continuities may only be apparent in this paper we report 40ar 39ar dates on muscovite biotite and hornblende from some of the same samples dated by u pb and samples that crop out very close to the dated samples the goal was to set constraints on the alternative interpretations of the metamorphic structural history these interpretations are as follows 1 u pb ages record different times of metamorphic crystallization and deformation and there are significant tectonic displacements the mappable continuities are only apparent 2 the structural and stratigraphic continuity is real and the range is due to localized heating and deformation events spanning 100 ma the relative uniformity of the

pre melt season sediment plume variability at jokulsarlon iceland a preliminary evaluation using in situ spectroradiometry and satellite imagery high latitude atmospheric warming is impacting freshwater cycling requiring techniques for monitoring the hydrology of sparsely gauged regions the submarine runoff of tidewater glaciers presents a particular challenge we evaluate the utility of moderate resolution imaging spectroradiometer modis imagery for monitoring turbid meltwater plume variability in the glacier lagoon jokulsarlon iceland for a short interval before the onset of the main melt season total suspended solids concentrations tss of surface waters are related to remotely sensed reflectance via empirical calibration between in situ sampled tss and reflectance in a modis band 1 equivalent wavelength window this study differs from previous ones in its application to an overturning tidewater glacier plume rather than one derived from river runoff the linear calibration improves on previous studies by facilitating a wider range of plume metrics than areal extent notably pixel by pixel tss values increasing values of minimum plume tss over the study interval credibly represent rising overall turbidity in the lagoon as melting accumulates plume extent responds principally to consistently strong offshore winds further work is required to determine the temporal persistence of the calibration but remote plume observation holds promise for monitoring hydrological outputs from ungauged or ungaugeable systems

short term discharge and suspended sediment fluctuations in the proglacial skeldal river north east greenland the summer discharge pattern of the skeldal river which drains a 560 km2 partly glacierized catchment in north east greenland is dominated by diurnal oscillations reflecting variations in the melt rate of snow and ice in the basin superimposed on this diurnal pattern are numerous short lived discharge fluctuations of irregular periodicity and magnitude the larger fluctuations are described and attributed to both rainfall events and periodic collapse of the glacier margin damming flow from beneath the skelbrae glacier other minor fluctuations are less readily explained but are associated with changes in the channelized and distributed reservoirs and possibly temporary blockage of subglacial conduits caused by ice melt with subsequent damming fluctuations in suspended sediment concentration ssc are normally associated with discharge fluctuations although examples of transient flushes were observed where marked increases in ssc occurred in the absence of corresponding discharge variations a strong relationship between the event discharge increase and event ssc increase for rainfall induced events was established but no such relationship existed for non rainfall induced events there is some evidence for an exhaustion effect in the ssc patterns both at the event time scale and as the month proceeds a mean suspended sediment load of 1765 0 26 t day 1 was estimated for the study period which would be equivalent to a suspended sediment yield of 732 4 t km 2 year 1 copyright 2001 john wiley sons ltd

linking metamorphic textures to u pb monazite in situ geochronology to determine the age and nature of aluminosilicate forming reactions in the northern monashee mountains british columbia abstract the monashee mountains of the canadian cordillera are thought to expose a classic barrovian facies series of isograds the timing of aluminosilicate growth in the region was determined for four pelitic schist samples by combining textural relationships with monazite compositional zoning and monazite u pb geochronology conducted directly on thin sections by the laser ablation method three distinct phases of kyanite growth are recorded in the kyanite zone at c 153 ma between 122 and 94 ma and between 76 and 58 ma for each phase monazite and garnet grew synchronously with kyanite probably by a reaction involving the breakdown of staurolite in contrast sillimanite growth by muscovite dehydration melting occurred at or before c 104 ma in the sillimanite zone and retrograde sillimanite grew in schists previously metamorphosed at the kyanite grade during the first two phases by the influx of hot acidic fluids during top to the east shearing at ca 71 ma these results indicate that rocks metamorphosed at different places and different times in the orogen were juxtaposed prior to being overprinted at the sillimanite grade in the late cretaceous early paleocene during the influx of hot fluids in a structurally coherent body deforming by easterly directed shearing this study also provides new insight into monazite petrogenesis and suggests that at least in some circumstances monazite formation is linked to the staurolite out reaction that produces kyanite

oxygen isotope study of quartz al2sio5 pairs from the mica creek area british columbia implications for the recovery of peak metamorphic temperatures oxygen isotope analyses of quartz al2sio5 pairs have been made for samples from the mica creek area british columbia we have analysed quartz kyanite nodules and quartz kyanite and quartz sillimanite in multiphase pelitic rocks from the staurolite kyanite kyanite and sillimanite zones apparent temperatures calculated from oxygen isotopic fractionation range from 555 c staurolite kyanite zone to 695 c sillimanite zone temperatures from the quartz kyanite nodules range from 630 to 675 c some of the nodules show isotopic disequilibrium most of the results confirm predictions that bimineralic rocks will yield an estimate of peak metamorphic temperatures when the less abundant mineral an aluminium silicate is the slower oxygen diffuser using cooling rates of 10 100 c ma 1 for the multiphase rocks measured crystal sizes and modes the fast grain boundary diffusion model with wet diffusion data ph2o 1 0 kbar yields predicted apparent temperatures which are generally lower than the measured apparent temperatures the agreement is improved if slower diffusion coefficients are used this suggests that f h2o during cooling was lower than that of the hydrothermal experiments and thus that there was little interaction with aqueous fluids of internal or external origin to modify the isotopic compositions the measured apparent isotopic temperatures and apparent garnet biotite fe mg exchange temperatures show very poor agreement for the sillimanite zone samples with the garnet biotite fe mg exchange temperatures generally higher than the oxygen isotope temperatures compared with the other calibrations that we tested the measured apparent temperatures using the sharp calibration show the best agreeement with recently published p t grids although some variability in agreement is expected due to variable f h2o during cooling

ocean regulation hypothesis for glacier dynamics in southeast greenland and implications for ice sheet mass changes synchronous acceleration and thinning of southeast se greenland glaciers during the early 2000s was the main contributor that resulted in the doubling of annual discharge from the ice sheet we show that this acceleration was followed by a synchronized and widespread slowdown of the same glaciers in many cases associated with a decrease in thinning rates and we propose that ice sheet ocean interactions are the first order regional control on these recent mass changes sea surface temperature and mooring data show that the preceding dynamic thinning coincides with a brief decline in the cold east greenland coastal current egcc and east greenland current we suggest this decline was partly induced by a reduction in ice sheet runoff which allowed warm water from the irminger current to reach the se greenland coast a restrengthening of the cold waters coincides with the glaciers subsequent slowdown we argue that this warming and subsequent cooling of the coastal waters was the cause of the glaciers dynamic changes we further suggest that the restrengthening of the egcc resulted in part from cold water input by increased glacier calving during the speedup and increased ice sheet runoff we hypothesize that the main mechanism for ice sheet mass loss in se greenland is highly sensitive to ocean conditions and is likely subject to negative feedback mechanisms copyright 2010 by the american geophysical union

scalings for submarine melting at tidewater glaciers from buoyant plume theory abstractrapid dynamic changes at the margins of the greenland ice sheet synchronous with ocean warming have raised concern that tidewater glaciers can respond sensitively to ocean forcing understanding of the processes encompassing ocean forcing nevertheless remains embryonic the authors use buoyant plume theory to study the dynamics of proglacial discharge plumes arising from the emergence of subglacial discharge into a fjord at the grounding line of a tidewater glacier deriving scalings for the induced submarine melting focusing on the parameter space relevant for high discharge tidewater glaciers the authors suggest that in an unstratified fjord the often quoted relationship between total submarine melt volume and subglacial discharge raised to the power is appropriate regardless of plume geometry provided discharge lies below a critical value in these cases it is then possible to formulate a simple equation estimating total submarine melt volume as a function of discharge fjord temperature

tectonic assembly of inverted metamorphic sequences inverted metamorphic sequences are characterized by peak metamorphic temperatures that increase structurally upward with isograds that are typically parallel to associated thrust faults a fully coupled thermal mechanical model for convergent orogens shows how an inverted sequence can be tectonically assembled in a crustal scale ductile shear zone at moderate to high rates of synorogenic erosion model inverted sequences form by tectonic juxtaposition of points with widely differing initial positions that reach peak temperatures at different times and in different places within the model orogen and thus do not represent metamorphic or thermal gradients inverted crustal isotherms are not required to produce model inverted isograds model results agree well with metamorphic pressure temperature data from the main central thrust zone of the central nepal himalayas

large and rapid melt induced velocity changes in the ablation zone of the greenland ice sheet continuous global positioning system observations reveal rapid and large ice velocity fluctuations in the western ablation zone of the greenland ice sheet within days ice velocity reacts to increased meltwater production and increases by a factor of 4 such a response is much stronger and much faster than previously reported over a longer period of 17 years annual ice velocities have decreased slightly which suggests that the englacial hydraulic system adjusts constantly to the variable meltwater input which results in a more or less constant ice flux over the years the positive feedback mechanism between melt rate and ice velocity appears to be a seasonal process that may have only a limited effect on the response of the ice sheet to climate warming over the next decades

suspended sediment yield and transfer processes in a small high arctic glacier basin svalbard observations of suspended sediment concentration and discharge at two sites on the proglacial river network draining from a predominantly cold based high arctic glacier austre broggerbreen are described analysis of these observations illustrates i the relatively low suspended sediment yield from this basin in comparison with many other glacier basins reported in the open literature ii sustained and possibly increasing availability of suspended sediment to the fluvial system as the ablation season progresses and iii the role of the proglacial sandur as both a sediment source and sink field observations coupled with the results of the data analysis are used to make inferences concerning the changing nature and relative importance of sediment sources within the basin 1998 john wiley sons ltd

meltwater and tidal currents controls on circulation in a small glacial fjord mcbride inlet is a small glacial fjord that receives freshwater from a submarine tunnel at the base of a tidewater glacier at its head the upwelling buoyant plume mixes with basin water lowering the salinity throughout the ice proximal basin freshwater also upwells from the melting ice face but the effects are only important in winter when discharge is low deep water renewal occurs in summer because the water mass crossing the sill inward is denser than the deep basin water the thick low velocity surface layer is affected by tides and wind producing a slow moving gyre near the glacier meltwater discharge from a submarine position and the resultant circulation in mcbride inlet result in extremely high ice proximal sedimentation rates

northern monashee mountains omineca crystalline belt british columbia timing of metamorphism anatexis and tectonic denudation the northern monashee mountains lie at the northern termination of a north south zone of eocene extension in the southern omineca crystalline belt of british columbia isotopic structural and petrogenetic studies in the northern monashee mountains document middle to late cretaceous regional metamorphism two episodes of crustal anatexis and a period of rapid cooling coincident with middle eocene extension partial melting of geochemically and isotopically similar pelitic sources produced peraluminous granites during and postdating regional metamorphism at 100 ma and 63 ma respectively rb sr muscovite whole rock isochrons from the younger granites give an age of 62 5 2 0 ma rb sr isochron and u pb mineral ages are similar indicating that the 63 ma granites were emplaced into a terrane that had cooled to 500 c or less by 63 ma hornblende muscovite and biotite k ar and apatite fission track mineral cooling ages from the northern monashee mountains are are 76 3 5 8 n 7 51 4 3 5 n 6 55 1 2 7 n 10 and 45 0 2 9 n 3 ma respectively mean age and standard deviation accelerated cooling beginning with the emplacement of 63 ma granites and ending at 45 ma occurred in response to ramping along a crustal scale thrust fault followed by offset on the middle eocene offset on the middle eocene north thompson normal fault

seasonal evolution of subglacial drainage and acceleration in a greenland outlet glacier an acceleration of ice mass loss has been observed near the margin of the greenland ice sheet partly as a result of faster ice motion observations by gps receivers reveal high seasonal variability in ice motion with summer motion up to 220 higher than winter background levels the greenland ice sheet contains enough water to raise sea levels by 7 m however its present mass balance and future contribution to sea level rise is poorly understood1 accelerated mass loss has been observed near the ice sheet margin partly as a result of faster ice motion2 3 4 surface melt waters can reach the base of the ice sheet and enhance basal ice motion5 6 however the response of ice motion to seasonal variations in meltwater supply is poorly constrained both in space and time here we present ice motion data obtained with global positioning system receivers located along a 35 km transect at the western margin of the greenland ice sheet throughout a summer melt season our measurements reveal substantial increases in ice velocity during summer up to 220 above winter background values these speed up events migrate up the glacier over the course of the summer the relationship between melt and ice motion varies both at each site throughout the melt season and between sites we suggest that these patterns can be explained by the seasonal evolution of the subglacial drainage system similar to hydraulic forcing mechanisms for ice dynamics that have been observed at smaller glaciers

the southern omineca belt british columbia new perspectives from the lithoprobe geoscience program geological isotopic and geochronology studies carried out by university and government researchers concurrently with the lithoprobe program have greatly refined our understanding of the regional geology crustal structure and tectonics of the omineca belt sound correlations have been established between surface geology and seismic reflection data cretaceous eocene thrust faults that are imaged in the subsurface in the shuswap complex may be part of a break forward thrust system that feeds into the purcell anticlinorium and the foreland belt the monashee decollement is the western continuation of the sole thrust beneath the foreland belt and provides a means of linking shortening across the entire orogen the thermal peak of metamorphism in the central and southern shuswap complex is now known to have occurred in the late cretaceous paleogene in contrast with earlier held views north american basement rocks are now known to extend beneath the eastern half of the canadian cordillera geochronology

multiple thermotectonic events in a continuous metamorphic sequence mica creek area southeastern canadian cordillera u th pb isotope dilution and shrimp dating indicates that multiple periods of metamorphism and deformation occurred between 160 and 60 ma in the mica creek area southeastern canadian cordillera the metamorphic sequence barrovian assemblages in the garnet zone through the sillimanite k feldspar zone fold generations and neoproterozoic stratigraphy are apparently continuous across the area yet it broadly lies between regions that were tectonized at different times middle jurassic to the east and middle cretaceous paleocene to the west our dating along a north lowest metamorphic grade to south highest grade transect shows that three km scale tectonic age domains exist in garnet schist of domain 1 peak metamorphism occurred at 163 ma and a minor thermal overprint occurred at 70 60 ma in migmatitic kyanite schist of domain 2 monazite inclusions in garnet grew at 110 ma matrix monazite and monazite inclusions in kyanite grew at 85 73 ma and rims of some grains grew at 60 ma kyanite growth during peak metamorphism must have occurred after 73 ma possibly during intrusion of 61 ma leucosome in migmatitic kyanite schist and sillimanite schist of domain 3 peak metamorphism occurred at 99 93 ma and lesser thermal events occurred at 280 160 110 and 70 ma we thus conclude that the thermal peak of metamorphism took place at different times in each domain with peak events coinciding with secondary events in other domains age constraints on s 1 2 are provided by dating variably deformed granitoid rocks s 1 2 developed before 72 ma in domain 1 at least partly at 61 58 ma and 122 63 ma in domains 2 and 3 respectively our findings show that the mica creek area is the only known region in the southeastern canadian cordillera that was affected by the five recognized major periods of tectonism 175 160 141 120 110 100 90 and 75 50 ma the key to understanding the geologic history is determining why several metamorphic and deformation events spanning 100 myr occurred within a single tectonometamorphic complex with apparent geologic continuity if continuity is only apparent the domains may have been tectonically assembled along cryptic unrecognized shear zones however if continuity does indeed exist the events must have been locally superimposed on the complex