the internal sediment architecture of a drumlin port byron new york state usa abstract an exposure within the central portion of a large drumlin at port byron new york state usa part of the large new york drumlin field reveals a sequence of steeply dipping cemented sands and gravels of proglacial ice contact deltaic origin overlain by a thin till veneer the sands and gravels appear to have been deposited within the proximal proglacial environment during a late retreat phase of the laurentide ice sheet sometime prior to being overridden by subsequent ice and drumlinized during deposition of the ice contact delta escaping subglacial regelation meltwater permeated the proximal deltaic sediment pile and calcium carbonate was released in a series of pulses to form pore occluding calcite cement within the sand and gravel porespaces the calcium carbonate precipitated into the sands and gravels due to a reduction in hydrostatic pressure and co2 outgassing of the meltwater as it exited from beneath the ice sheet once cemented these deltaic sediments were considerably stronger and acted afterward as an obstacle around which the future ice advance streamed and in turn produced the characteristic drumlin shape in overriding the ice contact deltaic sediments the ice sheet emplaced a thin layer of till which exhibits syndepositional deformation features indicative of being emplaced as a deforming bed layer beneath the advancing ice sheet micromorphological analysis of the overlying till shows that no interstitial or intraclastic calcite occurs within the till

vegetation history and climate in the savanna biome south africa since 190 000 ka a comparison of pollen data from the tswaing crater the pretoria saltpan and wonderkrater abstract the long term quaternary vegetation and climate history in south africa s savanna biome since ca 190 000 yr bp is elucidated by the palynological record of lake sediments in the tswaing crater the pretoria saltpan and spring deposits from wonderkrater despite hiatuses in both sequences palaeotemperature trends from the two places are presented by means of principal components analysis pca of pollen data allowing a new regional palaeoenvironmental reconstruction correlation in the older sections of the sequences beyond radiocarbon dating is tentative suggesting that the wonderkrater sequence is roughly 4 times younger than the tswaing sequence combined temperature indications from the two sites suggest cooling at ca 14 000 yr bp and slight warming at ca 15 000 yr bp although no data are available between ca 15 000 and 21 000 and 25 000 and 31 000 yr bp generally cool conditions are suggested between ca 11 000 and 33 000 yr bp between ca 33 000 and an extrapolated age of ca 80 000 yr bp at least three warmer pulses of varying intensity occurred no data are available between ca 80 000 and 150 000 yr but between 150 000 and ca 190 000 yr bp two cool and two moderately warm phases are suggested

persistent millennial scale climatic variability over the past 25 000 years in southern africa abstract data from stalagmites in the makapansgat valley south africa document regional climatic change in southern africa in the late pleistocene and holocene a new tims u series dated stalagmite indicates speleothem growth from 24 4 to 12 7 ka and from 10 2 to 0 ka interrupted by a 2 5 ka hiatus high resolution oxygen and carbon stable isotope data suggest that postglacial warming was first initiated 17 ka was interrupted by cooling probably associated with the antarctic cold reversal and was followed by strong warming after 13 5 ka the early holocene experienced warm evaporative conditions with fewer c4 grasses cooling is evident from 6 to 2 5 ka followed by warming between 1 5 and 2 5 ka and briefly at ad 1200 maximum holocene cooling occurred at ad 1700 the new stalagmite largely confirms results from shorter holocene stalagmites reported earlier the strongest variability superimposed on more general trends has a quasi periodicity between 2 5 and 4 0 ka also present are weaker 1 0 ka and 100 year oscillations the latter probably solar induced given similarities to the antarctic records the proximate driving force producing millennial and centennial scale changes in the makapansgat record is postulated to be atmospheric circulation changes associated with change in the southern hemisphere circumpolar westerly wind vortex

late quaternary paleotemperatures derived from a speleothem from cango caves cape province south africa abstract an oxygen isotope temperature record over a large part of the past 30 000 yr has been obtained for the southern cape province of south africa by combining data on the isotopic composition of a stalagmite from a deep cave with that of a confined groundwater aquifer in the same region results show that temperatures during the last glacial maximum were on average about 6 c lower than those today with peaks up to 7 c lower a detailed analysis of the past 5000 yr suggests multiple fluctuations with generally lower temperatures 1 2 c around 4500 and 3000 yr b p the carbon isotopic composition of the stalagmite indicates significant vegetation changes between the late pleistocene and today and also during the second half of the holocene

palynology of hyrax middens 2000 years of palaeoenvironmental history in namibia abstract well preserved and dateable faunal middens in rock shelters of dry areas in southern africa occur as desiccated urine rich masses under local conditions which exclude microbial decomposition and oxidation urine cements together faecal pellets and other inclusions nine radiocarbon dated hyrax procavia capensis dung middens from the kuiseb river basin of the namib desert were sub sampled and analysed for fossil pollen some contain small proportions of rat droppings but not many macro fossils comparative modern pollen in faecal samples were also studied most plant macro fossils are severely digested but seeds are well preserved some insect inclusions were identified small scale changes in vegetation over the last two millennia were observed representing environmental fluctuations in cycles of ca 100 200 years the fluctuations partly agree with other palynological data from southern africa and with geomorphologic evidence for environmental changes in the desert region

retreat of glaciar tyndall patagonia over the last half century we report measurements of ice surface elevation ice thickness and surface area for glaciar tyndall patagonia made in 1999 2002 the measurements together with previously published observations show acceleration over the last few decades of the rates of thinning and retreat of the main calving front the acceleration of shrinkage appears to be driven by a combination of climate and feedback processes the dominant feedback being increased melting associated with lowering of the glacier surface elevation feedback the melting capacity in the main terminus lake is now too small to be a major factor accelerating the retreat the glacier bed has low slope and remains below the elevation of the lake spillway for 14 km upstream from the 2000 calving front indicating the potential for extensive retreat under the influence of strong elevation feedback and increasing interaction with the lake as it enlarges

stabilizing feedbacks in glacier bed erosion glaciers often erode transport and deposit sediment much more rapidly than nonglacial environments1 with implications for the evolution of glaciated mountain belts and their associated sedimentary basins but modelling such glacial processes is difficult partly because stabilizing feedbacks similar to those operating in rivers2 3 have not been identified for glacial landscapes here we combine new and existing data of glacier morphology and the processes governing glacier evolution from diverse settings to reveal such stabilizing feedbacks we find that the long profiles of beds of highly erosive glaciers tend towards steady state angles opposed to and slightly more than 50 per cent steeper than the overlying ice air surface slopes and that additional subglacial deepening must be enabled by non glacial processes climatic or glaciological perturbations of the ice air surface slope can have large transient effects on glaciofluvial sediment flux and apparent glacial erosion rate

segmentation of the caledonian orogenic infrastructure and exhumation of the western gneiss region during transtensional collapse the ultra high pressure western gneiss region of the norwegian caledonides represents an archetypical orogenic infrastructure of a continent continent collision zone to test established exhumation models we synthesize the geochronology and structures of major basement windows and provide new ages from poorly dated areas migmatite u pb zircon samples date melt crystallization at c 405 ma in the oygarden complex expanding the spatial extent of devonian migmatization micas from shear zones in the oygarden and gulen domes yield 40ar 39ar ages mostly between 405 and 398 ma recording the exhumation of metamorphic core complexes on a larger scale the youngest ages of various geochronometers in different segments of the western gneiss region show abrupt breaks 10 30 myr across low angle detachments and sinistral transfer zones which also correspond to metamorphic and structural discontinuities we explain the segmentation of the orogenic infrastructure by partitioned post orogenic transtension due to lateral and vertical rheological contrasts in the orogenic edifice strong cratonic foreland and orogenic wedge v soft infrastructure differential crustal stretching dragged out deep levels of the orogenic crust below low angle detachments and became progressively dominated by sinistral transfer zones collapse obliterated the syn collisional structure of the orogenic root and resulted in the diachronous exhumation of distinct infrastructure segments supplementary material complete analytical results are available at https doi org 10 6084 m9 figshare c 5241710

instruments and methods a novel backpackable ice penetrating radar system we have developed a novel ice penetrating radar system that can be carried on a backpack including batteries for a 3 hour continuous measurement the total weight is 13 kg in addition it operates reliably down to 25 c has a low power consumption of 24 w and is semi waterproof the system has a built in one controller with a high brightness display for reading data quickly a receiver with 12 bit digitizing and a 1 kv pulse transmitter in which the pulse amplitude varies by 0 2 optical communications between components provides low noise data acquisition and allows synchronizing of the pulse transmission with sampling measurements with the system revealed the 300 m deep bed topography of a temperate valley glacier in the late ablation season

glacier volume estimation from ice thickness data applied to the muz taw glacier sawir mountains china in this work ground penetrating radar gpr data global position system gps data landsat remote sensing images and digital elevation model dem srtm were used to study the muz taw glacier in the sawir mountains by a variety of interpolation methods spatial pattern of thickness of the muz taw glacier was obtained the results show that there are obvious differences between the available gpr transverse profiles the lower transverse profile has typical u type topographic feature the maximum glacier thickness is up to 116 4 m glacier thickness distribution in the higher profile is relatively flat with an average about 70 90 m the longitudinal profile forms a ladder like distribution which in the middle of the ice bedrock topography has obvious depression the average longitudinal ice thickness is about 80 89 m the maximum ice thickness is up to 122 61 m in addition the preliminary estimation of the average thickness and total terminus ice volume were approximately 60 5 m and 0 195 km3 respectively

detrital muscovite 40ar 39ar ages from carboniferous sandstones of the british isles provenance and implications for the uplift history of orogenic belts major progradations of clastic sediments are recorded in the sedimentary record of the famennian and the visean namurian of the united kingdom and surrounding waters we have determined 40ar 39ar ages of 162 detrital muscovites from 11 coarse sandstones which were deposited between 370 and 465 ma spanning both progradations detrital mica ages are dominated by a peak at 415 ma with minor peaks at 440 ma and 390 ma the 415 ma muscovites are derived from the unroofing of the scandian nappes during the compressional phase of the caledonian orogeny in scandinavia the 440 ma muscovites record pre scandian orogenic activity which is rarely preserved in the orogenic record thermochronological evidence suggests that episodic postorogenic uplift and exhumation events kept the scandian orogen a major topographic feature and likely a sediment source for over 100 million years after nappe emplacement and implicates tectonic rather than climatic control on the clastic sediment progradations the near total absence of detrital muscovites with ages 415 ma suggests that the scandian nappes had not been entirely eroded despite repeated uplift during the postorogenic extension the river s which supplied the sediments probably ran parallel to the strike of the major scandian thrusts along the length of the caledonian orogen in a manner analogous to the major river systems of contemporary orogenic highlands

a time marker at 17 5 kyr bp detected throughout west antarctica deep radar soundings as part of the international trans antarctic scientific expedition us itase traverses in west antarctica have revealed a bright internal reflector that we have imaged throughout widespread locations across the ice sheet the layer is seen in traverses emanating from byrd station in four directions and has been traced continuously for distances of 535 km toward the weddell sea drainage 500 km toward south pole 150 km toward the executive committee range and 160 km toward kamb ice stream former ice stream c the approximate area encompassed by the layer identified in these studies is 250 000 km 2 if the layer identification can also be extended to siple dome where we have additional radar soundings jacobel and others 2000 the approximate area covered would increase by 50 in many locations echo strength from the layer rivals the bed echo in amplitude even though it generally lies at a depth greater than half the ice thickness at byrd station where the layer depth is 1260 m an age of 17 5 kyr bp has been assigned based on the blunier and brook 2001 chronology hammer and others 1997 note that the acidity at this depth is 20 times the amplitude of any other part of the core the depiction of this strong and widespread dated isochrone provides a unique time marker for much of the ice in west antarctica we apply a layer tracing technique to infer the depth time scale at the inland west antarctic ice sheet divide and use this in a simple model to estimate the average accumulation rate

seismic reflection evidence for a deep subglacial trough beneath jakobshavns isbrae west greenland seismic reflection methods were used to determine the ice thickness and basal topography of jakobshavns isbrae a large fast moving ice stream outlet glacier in west greenland a method of data analysis was developed which involves the pointwise migration of data from a linear seismic array and a single explosive source the method yields the depth horizontal position and slope of the basal reflector a deep u shaped subglacial trough was found beneath the entire length of the well defined ice stream the trough is incised up to 1500 m into bedrock and its base lies 1200 1500 m below sea level for at least 70km inland center line ice thickness along most of the channel is about 2500 m or about 2 5 times that of the surrounding ice sheet this prominent bedrock trough was not apparent in existing radio echo sounding data reflection coefficients indicate that much of the basal interface is probably underlain by compacted non deforming sediment the large ice thickness coupled with relatively steep surface slopes leads to high basal shear stresses 200 300 kpa along the ice stream the large shear stresses and lack of a deformable bed imply that internal deformation plays a dominant role in the dynamics of jakobshavns isbrae

comparison of stable carbon isotope ratios in the whole wood cellulose and lignin of oak tree rings abstract the stable carbon isotope ratios 13c of whole wood cellulose and acid insoluble lignin from annual latewood increments of quercus robur l from modern and sub fossil wood were measured and their potential use as palaeoenvironmental indicators examined the resulting time series demonstrate a very high degree of coherence with 13c of cellulose isotopically enriched by approximately 3 compared to 13c of lignin the 13c values of all three components are influenced by the climate of july and august modern whole wood retains the strongest climate signal perhaps because its composition is closest to that of leaf sugars in sub fossil wood there is no evidence that differential decay leads to fractionation of carbon within either cellulose or lignin but differential decay can alter the cellulose to lignin ratio

satellite derived volume loss rates and glacier speeds for the juneau icefield alaska we provide a high resolution map of elevation change rates dh dt at the juneau icefield jif southeastern alaska in order to quantify its contribution to sea level rise between 2000 and 2009 2013 we also produce the first high resolution map of ice speeds at the jif which we use to constrain flux and look for acceleration we calculate dh dt using stacked digital elevation models dems from the advanced spaceborne thermal emission and reflection radiometer aster instrument and the shuttle radar topography mission srtm taking into account srtm c band penetration via comparison with srtm x band elevations overall the jif is losing mass less rapidly 0 13 0 12mw e a than other alaskan icefields 0 79mw e a we determine glacier speeds using pixel tracking on optical image pairs acquired from 2001 to 2010 by aster from radar image pairs acquired between 2007 and 2011 and from radar interferometry in 1995 we detect seasonal speed variations but no interannual acceleration ruling out dynamics as the cause of the observed thinning thinning must therefore be due to the documented warming in the region flux measurements confirm this for mendenhall glacier showing that calving constitutes only 2 5 5 of mass loss there

exhumation of the high pressure tsakkok lens swedish caledonides insights from the structural and white mica 40ar 39ar geochronological record

40ar 39ar polyorogenic mineral age record within the central mauritanide orogen west africa the central mauritanide orogen in the vicinity of magta lahjar is characterized by several internally imbricated polydeformed and variably metamorphosed infrastructural allochthons which include 1 a calc alkaline igneous complex kelbe intrusive and el hneik t extrusive sequences 2 portions of an ophiolitic sequence el aoueija and oued amour units and 3 continental margin rift sequences fark ka association which include amphibolite low ti continental tholeiite dike protoliths mylonitic quartzite and kyanite schist several variably meta morphosed quartzitic supracrustal nappes g oua and sangarafa allochthons structurally overlie the infrastructural units 40 ar 39 ar incremental release ages have been determined for 10 hornblende and 22 muscovite concentrates prepared from various units of the infrastructural and supra structural allochthons hornblende from fark ka amphibolite is characterized by internally discordant spectra reflecting wide spread contamination with extraneous argon 36 ar 40 ar versus 39 ar 40 ar isotopic correlations are well defined for several concentrates and the resultant ages suggest that post metamorphic cooling occurred following distinct late proterozoic tectonothermal events at ca 700 720 ma and ca 640 650 ma muscovite within fark ka lithologies initially cooled through argon closure temperatures between ca 570 and 595 ma muscovite records similar post metamorphic cooling ages in the other infrastructural allochthons and in the g oua suprastructural allochthon these muscovite ages are interpreted to reflect cooling associated with widespread post orogenic uplift and are consistent with deposition of upper proterozoic lower paleozoic flysch in the proximal foreland tichilit el beida group the tichilit el beida group and correlative parautochthonous sequences djon ba group were penetratively deformed prior to the early ordovician 40 ar 39 ar incremental release analyses of 6 very fine grained white mica concentrates from mylonitic quartzite along thrust faults within the parautochthon indicate that this deformation occurred prior to ca 540 550 ma there is no clear thermal record of this orogenic activity in either infrastructural or suprastructural allochthons suggesting that it must have occurred at relatively high structural levels and was probably largely of intracontinental character all foreland units were affected by post emsian folding effects of this tectonic activity are widespread throughout the parautochthon and western metamorphic sequences these effects include emplacement of the suprastructural allochthons into their present structural positions at ca 300 325 ma with an associated partial rejuvenation of muscovite argon systems proximal to basal thrust faults local reactivation of older thrust faults within the parautochthon and infrastructural allochthons is also indicated by variable 300 325 ma rejuvenation of muscovite argon systems within some fault zones muscovite within westernmost exposures of the infra structural allochthons was totally rejuvenated during the early carboniferous and records 300 m y plateau ages the early tectonic history recorded within the central mauritanide orogen appears to have been related to restricted rifting of a western crustal block from the west african craton and formation of a limited intervening oceanic domain subsequent closure resulted in compression and imbrication of continental crust with resultant development of an ensialic volcanic arc calc alkaline sequences within the infrastructural allochthons together with widespread metamorphism and deformation between ca 700 and 650 ma later orogenesis at ca 550 ma could have reflected distal effects of collisional events which dominate the rokelide orogen in sierra leon and guinea late paleozoic tectonotherma activity within the central mauritanides is interpreted to have developed as a result of a renewed translation between the western continental block and the west african craton during final collision of laurentia arc gondwana

an improved coherent radar depth sounder the university of kansas developed a coherent radar depth sounder during the 1980s this system was originally developed for glacial ice thickness measurements in the antarctic during the field tests in the antarctic and greenland we found the system performance to be less than optimum the field tests in greenland were performed in 1993 as a part of the nasa program for arctic climate assessment parca we redesigned and rebuilt this system to improve the performance the radar uses pulse compression and coherent signal processing to obtain high sensitivity and fine along track resolution it operates at a center frequency of 150 mhz with a radio frequency bandwidth of about 17 mhz which gives a range resolution of about 5 m in ice we have been operating it from a nasa p 3 aircraft for collecting ice thickness data in conjunction with laser surface elevation measurements over the greenland ice sheet during the last 4 years we have demonstrated that this radar can measure the thickness of more than 3 km of cold ice and can obtain ice thickness information over outlet glaciers and ice margins in this paper we provide a brief survey of radar sounding of glacial ice followed by a description of the system and subsystem design and performance we also show sample results from the field experiments over the greenland ice sheet and its outlet glacicrs

carbon isotope behaviour in wood and cellulose during artificial aging abstract modern wood was subjected to an artificial decay process to investigate its behaviour with respect to the stable carbon isotope composition of wood and the corresponding cellulose four different woods were used namely oak quercus robur beech fagus sylvatica pine pinus sylvestris sequoia sequoiadendron giganteum and pure spruce cellulose the process of decay was simulated by heating samples in water at 180 c from minutes to months during the decay period the carbon content of wood increased to almost 70 while the cellulose content decreased gradually to zero the degradation proceeds according to a two stage process an initial very fast break down is followed by a rather slow degradation after a strong discrimination against 13 c during the initial phase the 13c 12c ratio increases again mostly up to its initial value the carbon isotope trend for cellulose shows a similar pattern though it is less pronounced maximum discrimination was 1 relative to the untreated wood 13c values of cellulose decreased by up to 0 3 the 13 c depletion is presumably a consequence of the preferential decomposition of cellulose as compared to lignin data on fossil trees are compared with the results obtained from this treatment of aging the 13 c decrease is in line with observations from these fossil woods but the ensuing 13 c enrichment is at most weakly to be seen

instruments and methods an improved transient type ice penetrating radar a low cost compact short pulse ice penetrating radar ipr system with a center frequency of 50 mhz for sounding glacier topography is presented the radar was developed to measure ice thickness and to image internal structures and basal conditions of glaciers and ice sheets with a maximum range of 16 000 ns and a depth resolution better than 2 5 m the receiver of the ipr system employs asynchronous operation mode avoiding the need for a cable between the transmitter and receiver a new sampling technology using a high speed field programmable gate array which implements a 256 trace stacking algorithm to realize the analog to digital conversion both simplifies the structure of the receiver and increases the sampling efficiency the power consumption of the whole receiver is 1 5 w which can be supplied by a laptop computer test measurements were made during the 5th china expedition to the grove mountains in east antarctica field tests show the capability of this system to measure ice thickness up to 650 m and to define internal layers within the ice body

rainfall control of the δ13c ratios of mimusops caffra from kwazulu natal south africa high precision radiocarbon dating of individual growth rings demonstrates that mimusops caffra produces annual growth rings direct comparison of the carbon isotope composition of the annual rings from two specimens from the northern coast of kwazulu natal south africa with the historic climatic record that exists from ad 1927 shows a response to the amount of rainfall recorded for each year the 13 c response is particularly sensitive to extreme events such as tropical cyclones and droughts it is demonstrated that whole wood samples provide an accurate record of climatic conditions although the result allows long term periodicity in rainfall to be determined over the 134 years during which the oldest tree grew the last 20 years is overprinted with a 13 c shift of anthropogenic origin signal processing approaches allow the interannual rainfall response to be separated from the long term anthropogenic influences

ice motion of the patagonian icefields of south america 1984 2014 2015 american geophysical union all rights reserved we present the first comprehensive high resolution mosaic of ice velocity of the northern npi and southern patagonian icefields spi from multiple synthetic aperture radar and optical data collected between 1984 and 2014 the results reveal that many of the outlet glaciers extend far into the central ice plateaus which implies that changes in ice dynamics propagate far inside the accumulation area we report pronounced seasonal to interannual variability of ice motion on pio xi and jorge montt a doubling in speed of jorge montt a major slow down of o higgins significant fluctuations of upsala and a deceleration of san rafael which illustrate the need for sustained continuous time series of ice motion to understand the long term evolution of the rapidly thinning icefields the velocity product also resolves major ambiguities in glacier drainage in areas of relatively flat topography illustrating the need to combine topography and flow direction to map drainage basins

thermal history of thrust sheets in an orogenic wedge 40ar 39ar data from the polymetamorphic seve nappe complex northern swedish caledonides the seve nappe complex in the scandinavian caledonides contains the fragmented late precambrian continent ocean transition between baltica and the iapetus ocean this passive margin was fragmented and thrust eastwards over the baltic shield during caledonian orogenesis the individual thrust sheets in the seve nappe complex went through different p t t evolutions resulting in dramatic metamorphic contrasts eclogite bearing nappes are juxtaposed with nappes showing no evidence of caledonian deformation or metamorphism in their interiors strain localization to the marginal parts of the thrust sheets left records of both pre orogenic rift and early orogenic subduction and subsequent uplift processes in the thrust sheets of the seve nappe complex even though it has been transported several hundred kilometres only the margins of the eastern part of the sarektjakka nappe are affected by penetrative caledonian deformation this part of the sarektjakka nappe is dominated by pristine tholeiitic dykes and cross bedded sandstones the dykes are 608 1 ma old and make up 70 80 of the nappe widely spaced thin shear zones of the ruopsok fault system represent the only caledonian penetrative deformation in the interior of the nappe previously published ar ar dates indicate cooling below the closure temperature of hornblende at c 470 ma but numerous ages have been recorded ar dating of biotite and muscovite from a cross laminated metapsammite in the sarektjakka nappe gave well defined ages of 428 5 3 6 and 432 4 3 8 ma respectively muscovite from a shear zone in the ruopsok fault system gave 428 2 4 0 ma whereas hornblende from the same locality did not yield interpretable data the results indicate that these rocks were completely degassed at some unknown time presumably at the emplacement of the dyke swarm no subsequent excess argon contamination can be detected a likely candidate for the degassing event is the emplacement of the dykes at 608 ma the interior of the nappe and thus the entire nappe complex cooled below 350 c at around 430 ma cooling from more than 500 c at c 470 ma to 350 c at c 430 ma suggests an average cooling rate of 4 c ma a prolonged period of slow cooling exhumation following the initial rapid uplift of the eclogite bearing nappes and early ordovician construction of the seve nappe complex is suggested

protracted shearing at midcrustal conditions during large scale thrusting in the scandinavian caledonides during continental collision large tracts of crust are mobilised along major shear zones the metamorphic conditions at which these zones operate the duration of thrusting and the deformation processes that facilitated hundreds of km of tectonic transport are still unclear in the scandinavian caledonides the lower seve nappe displays a main mylonitic foliation with thickness of 1 km this foliation is overprinted by a brittle to ductile deformation pattern localized in c and c type shear bands proximal to the tectonic contact with the underlying sarv nappe thermobarometry of amphibolites and micaschists suggest a first high pressure stage at 400 500 c and 1 1 3 gpa recorded in mineral relics the main mylonitic foliation developed under epidote amphibolite facies conditions along the retrograde path from 600 c and 1 gpa to 500 c and 0 5 gpa age dating of synkinematic titanite grains in the amphibolites indicates that this mylonitic fabric formed at around 417 9 ma but older ages spanning 460 430 ma could represent earlier stages of mylonitization the shear bands developed at lower metamorphic conditions of 300 400 c and 0 3 gpa in the micaschists the recrystallized grain size of quartz decreases towards the shear bands monomineralic quartz layers are eventually dismembered to form polyphase aggregates deforming by dominant grain size sensitive creep accompanied by slip in muscovite and chlorite plagioclase zoning truncations suggest that the shear bands originated by fracturing followed by ductile deformation the results suggest protracted and long lasting shearing under amphibolite to greenschist facies conditions during the juxtaposition stacking and exhumation of the lower seve nappe

till beneath ice stream b 3 till deformation evidence and implications most of the velocity of ice stream b near the upstream b camp upb west antarctica appears to arise from deformation of a seismically detected subglacial till layer that averages 6 m thick available evidence indicates that the entire thickness of this till layer is deforming and is eroding subjacent bedrock into flutes parallel to ice flow and hundreds of meters across the resulting till flux beneath upb is equivalent to an average erosion rate of about 0 4 mm yr 1 in the catchment area and suggests that till deltas tens of kilometers long have been deposited at the grounding line during the holocene such deltas should be characterized by partial ice till decoupling across a water film and by a small ice air surface slope they may have been discovered by recent geophysical work

a low cost glacier mapping system an old portable 60 mhz radar has been upgraded with a new digital data processing and acquisition system and a new antenna construction enabling a fast and low cost installation on atwin otter aircraft augmented by a laser altimeter and kinematic global positioning system gps the system has the capability of acquiring accurate data on location and ice surface elevation and adequate quality data on ice thickness the system has been applied successfully in mapping the nioghalvfjerdsfjorden glacier northeast greenland in spite of the difficult conditions with melting water on the glacier surface the measurements from the floating part of the glacier have been evaluated by comparison of radar data with laser altimeter and in situ measurements

polyphase late paleozoic tectonothermal evolution of the southwestern meguma terrane nova scotia evidence from 40ar 39ar mineral ages 40ar 39ar incremental release ages of hornblende muscovite and biotite from a variety of granitic stocks and host metamorphic rocks suggest a complex late paleozoic tectonothermal evolution for the southwestern meguma terrane regional d1 folding with cleavage formation under greenschist lower amphibolite facies m1 metamorphic conditions occurred at ca 400 410 ma and was followed by emplacement of a series of granitic stocks ranging in age between ca 375 and 315 ma these were emplaced at relatively shallow crustal levels and developed contact metamorphic aureoles of variable grade these are locally superposed on m1 regional metamorphic assemblages and result in a complex isograd pattern 40ar 39ar mineral ages suggest episodes of contact metamorphism occurred at 1 360 375 ma possibly related to emplacement of the south mountain batholith or temporal equivalents 2 350 356 ma around the port mouton pluton and northeastern shelburne pluton 3 ca 315 325 ma near the wedgeport pluton and in

tectonics of the scandian orogeny and the western gneiss region in southern norway two crust forming events dominate the precambrian history of the western gneiss region wgr at about 1800 1600 ma and 1550 1400 ma the influence of the sveconorwegian orogeny 1200 900 ma is restricted to the region south of moldefjord romsdalen a series of anorthosites and related intrusives are present possibly derived from the now lost western margin of the baltic craton that may have been emplaced in the wgr as an allochthonous unit before the ordovician

thermochronology of economic mineral deposits dating the stages of mineralization at panasqueira portugal by high precision 40 39 ar age spectrum techniques on muscovite 40 ar 39 ar age spectrum dates for 13 muscovites have been used to reconstruct the thermal history thermochronology of the panasqueira portugal tin tungsten deposit a deposit spatially associated with a belt of hercynian plutons muscovite samples with an age difference as small as 2 2 m y 0 7 of the age are statistically distinct statistics are even better for comparison of multiple samples from separate events that is a difference of 0 9 m y 0 3 can be resolved in this approximately 300 m y old deposit the major tin and tungsten ore forming stages which are the oxide silicate stage the main sulfide stage and greisenization occurred between 296 3 or 0 8 1 sigma and 291 6 or 0 8 m y 1 sigma the first substage of the oxide silicate stage was a short lived thermal pulse at 296 3 or 0 6 m y the fluids responsible may have emanated from the known granite cupola the main sulfide stage was active at 294 5 or 0 9 m y as a slightly longer lived pulse with oldest evidence for this stage 295 8 or 0 6 m y coming from areas farthest away from the known cupola and youngest evidence 293 5 or 0 8 m y closest to the cupola a second substage of the oxide silicate stage occurred as a short lived thermal pulse at 292 9 or 0 7 m y synchronous with greisenization of the cupola and alteration of the silica cap at 292 1 or 0 4 m y the duration of activity of the oxide silicate stage the main sulfide stage greisenization and alteration of the silica cap based on the ages of all 13 muscovites was greater than 4 2 or 0 5 m y 1 sigma minor argon loss from all dated muscovites occurred during later reheating probably during the longer lived pyrrhotite alteration stage a single center the known cupola had a prolonged role and was the source for main sulfide stage oxide silicate stage ii greisenization and alteration of the silica cap and possibly oxide silicate stage i and the pyrrhotite alteration stage however a separate source for these latter two stages cannot be ruled out this study is an example of a new and powerful application of 40 ar 39 ar age spectrum dating of muscovite because of the high precision demonstrated in this study it is now possible to establish time constraints necessary for solving some of the long standing problems in economic geology beyond this the unique geologic situation of panasqueira has allowed us to quantify the thermal characteristics of muscovite published fluid inclusion data have been used to estimate a muscovite argon closure temperature of approximately 325 degrees c during rapid cooling or short reheating and a temperature of approximately 270 degrees c during slow cooling or extended reheating argon loss patterns displayed by all dated muscovites resulted from reheating after original closure the mechanism for this argon loss appears to have been argon transport by volume diffusion thus 40 ar 39 ar age spectrum dating of muscovite can be used to evaluate thermal conditions controlling argon diffusion as well as age duration and number of episodes of mineralization

a low frequency ice penetrating radar system adapted for use from an airplane test results from bering and malaspina glaciers alaska usa ice thickness measurements are needed to calculate fluxes through fast flowing outlet glaciers in greenland alaska patagonia and antarctica however relatively high attenuation of radio waves by dielectric absorption and volume scattering from englacial water hampers detection of the bed through warm deep ice in the past we have had success measuring ice thickness of temperate glaciers using a ground based monopulse radar system operating at low frequencies 2 mhz here we adapt the same system to operate from an airplane test flights over bering glacier alaska usa detected the bed through ice up to 1250 m thick flights across the seward malaspina glacier system alaska resolved the ice thickness of malaspina glacier but strong hyperbolic shaped returns obscured the bed echo through the seward throat it is likely that this clutter in the signal was caused by off nadir returns from chaotic surface crevasses that are ubiquitous in the throat region

the laidlaw volcanics a late silurian point on the geological time scale mapping mineralogical and chemical studies of an area west and northwest of canberra southeastern australia have shownthat the laidlaw volcanics are unique in the region and that their age is tightly controlled stratigraphically as they lie both above and below early ludlow late silurian fossiliferous sediments k ar mineral analyses previously published rb sr mineral analyses and new rb sr wholerock and mineral analyses together give the laidlaw volcanics an age of 420 7 2 2 m y this result for the early ludlow is identical numerically with a recently published age of 421 3 m y for the ashgillian late ordovician stockdale rhyolite and suggests either that the time interval between the ashgill and ludlow does not exceed a few million yearsor that the age estimate for the stockdale rhyolite is too young

holocene monsoon climate documented by oxygen and carbon isotopes from lake sediments and peat bogs in china a review and synthesis there has been much recent debate about holocene climate variation in the monsoon region of china especially the temporal pattern of variations in precipitation the time transgressive nature of the holocene precipitation maximum and the extent to which variations in regions influenced by the indian summer monsoon ism and the east asian summer monsoon easm have been synchronous we summarize and compare carbonate oxygen isotope records delta o 18 carb from ten lakes within the present day ism region we discuss their paleoclimate significance considering the present day moisture source isotopic composition of precipitation and the hydrological setting the delta o 18 carb records are controlled mainly by the isotopic composition of lake water which in turn is a function of regional precipitation evaporation p e balance and the proportion of precipitation that is monsoon derived we normalized the delta o 18 carb data and used these records to generate an integrated moisture index this index along with oxygen isotope records from speleothems and carbon isotope records delta c 13 org from peats within the monsoon region suggests that holocene climate was broadly synchronous across the monsoon region and within the limits of accuracy of the existing age models provides no strong evidence for previously proposed anti phasing of the ism and the easm stable isotope records from lake sediments and peat bogs have excellent potential for providing high quality paleoclimate data for monsoon asia and complement high resolution speleothem sequences which are only found in certain localities c 2011 elsevier ltd all rights reserved

rapid subglacial erosion beneath pine island glacier west antarctica we present measurements of ice thickness gravimetry and surface elevation on pine island glacier west antarctica separated by a period of 49 years at one station on the main trunk of the glacier we measured a surface elevation lowering with no significant change in ice thickness we interpret these as indicating subglacial erosion of 31 8 13 4 m at this location at a mean rate over the measurement period of 0 6 0 3 m a 1 and suggest that a current erosion rate of 1 m a 1 is possible our results emphasize that locally basal processes can have a significant effect on ice sheet changes particularly where fast flowing ice has an easily erodible bed

ground penetrating radar antenna orientation effects on temperate mountain glaciers abstractground penetrating radar gpr surveys on glaciers are generally restricted to a single pair of bistatic dipole antennas orientated either parallel or perpendicular to the surveying direction extensive helicopter borne and ground based gpr investigations on the glacier d otemma switzerland demonstrated that the detectability of the ice bedrock interface varies substantially with dipole orientation we recorded several across and along profiles using two different commercial gpr systems operated with 15 25 50 and 70 mhz antennas dipole alignments parallel to the glacier flow generated considerably stronger and more coherent bedrock reflections compared with a perpendicular dipole setup we observed the behavior for all the systems and antenna frequencies that we used to help explain these findings we performed 3d numerical modeling using the open source software gprmax simulations with 20 mhz transmitting and receiving dipoles indicated that the changes of the bedrock reflection amplitude

modeling the evolution of the juneau icefield between 1971 and 2100 using the parallel ice sheet model pism we study the evolution of the juneau icefield one of the largest icefields in north america 3700 km 2 using the parallel ice sheet model pism we test two climate datasets 20 km weather research and forecasting model wrf output and data from the scenarios network for alaska planning snap derived from spatial interpolation of observations good agreement between simulated and observed surface mass balance was achieved only after substantially adjusting wrf precipitation to account for unresolved orographic effects while snap s climate pattern is incompatible with observations of surface mass balance using the wrf data forced with the rcp6 0 emission scenario the model projects a decrease in ice volume by 58 68 and a 57 63 area loss by 2099 compared with 2010 if the modeled 2070 99 climate is held constant beyond 2099 the icefield is eliminated by 2200 with constant 1971 2010 climate the icefield stabilizes at 86 of its present day volume experiments started from an ice free state indicate that steady state volumes are largely independent of the initial ice volume when forced by identical scenarios of climate stabilization despite large projected volume losses the complex high mountain topography makes the juneau icefield less susceptible to climate warming than low lying alaskan icefields

noble gas and halogen evidence for the origin of scandinavian sandstone hosted pb zn deposits abstract fluid origins in the sandstone hosted pb zn class of ore deposit have been investigated in three deposits from scandinavia laisvall vassbo and osen the deposits studied are hosted by autochthonous cambrian sandstones that preserve a near original structural relationship to the underlying precambrian basement enabling the role of basement interaction to be assessed mineral samples have been collected from across the paragenetic sequence sphalerite galena pyrite fluorite and barite of impregnation and related joint hosted mineralization fluid inclusion halogen cl br and i and noble gas isotope 40 ar 36 ar 84 kr compositions were determined simultaneously by noble gas mass spectrometry of irradiated sample splits complementary he isotope analyses are obtained from nonirradiated splits of the same samples 3 he 4 he values at laisvall and osen are highly radiogenic 0 02 ra and the 4 he 40 ar ratio extends to values greater than the crustal production value of 5 characteristic of low temperature crustal fluids at vassbo a slightly elevated 3 he 4 he ratio of 0 1 0 3 ra is compatible with a very minor mantle component 1 4 suggesting a distal source for the basinal brine dominated fluid br cl molar ratios 3 2 8 2 10 3 are greater than the present seawater value of 1 54 10 3 and correspond with i cl molar ratios in the range 64 1600 10 6 the upper limits of both the i cl and br cl values are amongst the highest measured in crustal fluids together the data indicate acquisition of salinity by the evaporation of seawater beyond the point of halite saturation and subsequent fluid interaction with i rich organic matter in the subsurface the data are compatible with the independent transport of sulfate and sulfide and indicate that fluids responsible for joint hosted mineralization were distinct to those responsible for impregnation mineralization all three deposits preserve fluids with 40 ar 36 ar in the range of 6 000 10 000 and fluid inclusion 40 ar concentrations of 0 02 0 05 cm 3 cm 3 fluid inclusion 4 he concentrations are also extremely elevated with maximum values of 0 1 cm 3 cm 3 in laisvall fluorite and sphalerite the high 40 ar 36 ar values together with the high 4 he and 40 ar concentrations result from a very long premineralization crustal residence time on the order of 100 200 ma together the noble gas and halogen data are compatible with a caledonian mineralization event 425 ma caused by mixing of two or more long lived hydrothermal basinal brines and pore fluids at the sites of mineralization the data suggest negligible recharge of the basinal brines by meteoric water and indicate extensive fluid basement interaction before mineralization the similar noble gas composition of each deposit suggests that similar processes operated at all three deposits and favors a single pass fluid flow model for mineralization

ice thickness of the northern half of the patagonia icefields of south america from high resolution airborne gravity surveys author s gourlet p rignot e rivera a casassa g abstract 2015 american geophysical union all rights reserved we employ high resolution high precision helicopter borne gravity observations of the northern npi and southern patagonia icefields spi south america to infer ice thickness and bed topography using a three dimensional model constrained by fjord and lake bathymetry and a land ice mask the results reveal thicker ice than the reflecting horizon of radar sounders with 1 km deep ice for glaciar san rafael and colonia npi and 1 5 km deep ice for glaciar occidental spi these bedrock troughs channelize fast motion of ice from the plateaus combining ice motion and thickness we calculate balance accumulation levels of 3 6 m yr water equivalent for the plateaus bed elevation remains below sea lake level 15 20 km inland for jorge montt and o higgins which favors retreat and is at sea level for san rafael which halted its retreat the results demonstrate the utility of airborne gravity surveys for providing critical data on ice volume bed elevation and balance accumulation of temperate ice masses

protolith ages and exhumation histories of ultra high pressure rocks across the western gneiss region norway the timing of protolith formation ultrahigh pressure uhp subduction and subsequent exhumation for the ultrahigh pressure to high pressure units across the eastern part of the western gneiss region norway were assessed using u pb zircon th pb monazite and 40 ar 39 ar white mica ages u pb zircon ages from eclogites demonstrate that oceanic and continental allochthons were emplaced onto the baltica basement before the entire mass was subducted to ultra high pressure eclogites within the allochthons across the entire western gneiss region are caledonian and show a degree of zircon re crystallization that increases with peak pressure permitting the interpretation that the entire region underwent synchronous subduction 40 ar 39 ar white mica ages of 399 ma indicate that the eastern part of the western gneiss region had been exhumed to shallow crustal levels while uhp metamorphism was ongoing farther west indicating a westward dip to the slab the 40 ar 39 ar white mica ages also show a clear east to west gradient across the entire western gneiss region indicating that the western gneiss region rose diachronously to crustal levels from east to west between 399 and 390 ma

the influence of drainage boundaries on specific mass balance results a case study of engabreen norway mass balance measurements were initiated on engabreen an outlet glacier from the svartisen ice cap norway in 1970 the glacier boundary was defined based on where meltwater drained as the interest in engabreen was mainly hydrological however the apparent discrepancy between the calculated cumulative glacier mass balance since 1970 and changes in glacier geometry prompted a re examination of the glacier boundary the glaciological drainage boundary is defined by studying whether ice flow physically contributes to engabreen tongue and corresponds to a glacier with an area of 27 2 km 2 significantly smaller than that defined by the hydrological drainage boundary at 39 6 km 2 this glaciological drainage boundary is here named the ice flow perimeter the area difference between this and the hydrological drainage boundary is largest for the altitudinal range 1300 1400 m a s l generally the glaciological glacier is lower in mean altitude than the hydrological glacier and this affects the calculated specific mass balance using the glaciological boundary leads to reductions in mean annual winter and summer balance when spatial differences are ignored of 0 12 m w e from 2 92 to 2 80 m w e and 0 15 m w e from 2 32 to 2 47 m w e respectively the reduction in mean net balance for the period 1970 2006 is 0 27 m w e from 0 59 to 0 32 m w e which is about 50 of the calculated mass surplus in this period this illustrates that the choice of glacier outline can significantly influence the long term cumulative mass balance and that results from outlet glaciers must be interpreted with care when used for regional estimates of glacier change

declining trend in the 13c 12c ratio of atmospheric carbon dioxide from tree rings of south african widdringtonia cedarbergensis abstract stable carbon isotope chronologies using tree ring wood cellulose have proved useful for developing hypotheses on climate and environment change however within both the southern hemisphere and africa there has been very little tree ring based isotope research here we report the first high resolution annual 13 c 12 c chronology for both africa and the southern hemisphere the 77 yr stable carbon isotope chronology was developed from six widdringtonia cedarbergensis trees from a site in the cedarberg mountains western cape province south africa the results indicate that 13 c 12 c ratios are not different from 1900 to 1949 after 1949 however values become significantly more negative to 1977 the isotopic record from the pooled trees at the die bos site does not correlate with rainfall this correlation is not significant even when the widdringtonia stable carbon isotope record is de trended for the anthropogenic co 2 contribution the widdringtonia record does however correlate significantly with atmospheric 13 c 12 c co 2 values derived from ice core data tree ring 13 c 12 c chronologies from the northern hemisphere and recent southern hemisphere records

40ar 39ar and rb sr age determinations on quaternary volcanic rocks 40 ar 39 ar and rb sr ages have been measured on separated minerals from the potassic volcanics of the roman comagmatic region to test the ability of these methods to accurately data quaternary geological events the very high k and rb contents of the roman magmas present particularly favorable situations in which the very high concentrations of the radioactive nuclides 40 k and 87 rb result in well resolved in situ enrichments of the daughter isotopes despite the very young ages six leucite separates contained ar with very high bulk 40 36 ratios above 1000 and in which the 40 ar and the 39 ar were very well correlated yielding well defined ages averaging 3 38 0 08 10 5 years two leucites contained ar with lower bulk 40 36 ratios 400 and in at least two release steps from these leucites the 40 ar 36 ar ratio was significantly lower than atmospheric despite the uncertainty in the composition of the trapped component these two leucites have ages that do not differ significantly from the ages of the other leucites for the biotites it was not possible to obtain through stepwise degassing a good separation of in situ radiogenic 40 ar from trapped 40 ar and therefore the calculated ages are not as precise as those of the leucites in three cases the biotite age agrees with the age of the cogenetic leucite but in the remaining two cases discordant ages are obtained suggesting caution when using biotites as quaternary age indicators rb sr measurements on leucite biotite and pyroxene separates hand picked from each of three tuff samples yielded a dispersion in 87 sr 86 sr as large as 16 parts in 10 4 and 87 rb 86 sr as high as 218 for leucites and permitted the determination of internal isochron ages the ages obtained range from 3 8 0 2 10 5 to 3 3 0 2 10 5 years and are in good agreement with the 40 ar 39 ar ages on the leucites the data for each tuff sample yield a well defined uniform initial 87 sr 86 sr however different tuffs show small differences in initial 87 sr 86 sr pointing to distinct sources or to assimilation of different materials during the extrusion of the tuffs these measurements demonstrate the possibility of dating quaternary materials by both the 40 ar 39 ar method and the rb sr method the observation of concordant ages with a precision of a few percent represents a powerful tool in quaternary stratigraphy

ice thickness measurements and volume estimates for glaciers in norway glacier volume and ice thickness distribution are important variables for water resource management in norway and the assessment of future glacier changes we present a detailed assessment of thickness distribution and total glacier volume for mainland norway based on data and modelling glacier outlines from a landsat derived inventory from 1999 to 2006 covering an area of 2692 81 km 2 were used as input we compiled a rich set of ice thickness observations collected over the past 30 years altogether interpolated ice thickness measurements were available for 870 km 2 32 of the current glacier area of norway with a total ice volume of 134 23 km 3 results indicate that mean ice thickness is similar for all larger ice caps and weakly correlates with their total area ice thickness data were used to calibrate a physically based distributed model for estimating the ice thickness of unmeasured glaciers the results were also used to calibrate volume area scaling relations the calibrated total volume estimates for all norwegian glaciers ranged from 257 to 300 km 3

delineation of a complexly dipping temperate glacier bed using short pulse radar arrays we have defined the complex bed topography for a section of a small temperate glacier using 50 mhz monostatic short pulse radar data and a synthetic aperture array processing method the data were collected on a 100 m by 340 m array grid in the upper stem of gulkana glacier central alaska u s a the array processing was based on a modified three dimensional 3 d kirchhoff migration integral and implemented with a synthetic aperture approach that uses sequences of overlapping sub arrays to generate depth images in vertical planes typical sub array beam patterns are generally 5 at the 6 db level giving a flashlight like searching capability without distorting the wavelet shape the bed topography was constructed using normal reflections picked from 3 d array depth images in some instances reflections were imaged outside the data coverage area the bed surface dips steeply both parallel and transverse to the direction of ice flow the maximum observed depth is roughly 140 m the 3 d method resolved bed dips up to 45 in regions of steepest dip it improved depth accuracy by 36 compared with raw data and by 15 compared with standard two dimensional 2 d migration over 12 db of signal to noise improvement and improved spatial resolution was achieved compared to raw data and 2 d migration false bottom layering seen in the raw data and in 2 d migrations is not observed in the 3 d array results furthermore loss of bottom reflections is shown by the 3 d migration to be attributable to the dip and curvature of the reflector and not scattering losses or signal clutter from englacial inclusions

distributed ice thickness and volume of all glaciers around the globe 1 a new physically based approach for calculating glacier ice thickness distribution and volume is presented and applied to all glaciers and ice caps worldwide combining glacier outlines of the globally complete randolph glacier inventory with terrain elevation models shuttle radar topography mission advanced spaceborne thermal emission and reflection radiometer we use a simple dynamic model to obtain spatially distributed thickness of individual glaciers by inverting their surface topography results are validated against a comprehensive set of thickness observations for 300 glaciers from most glacierized regions of the world for all mountain glaciers and ice caps outside of the antarctic and greenland ice sheets we find a total ice volume of 170 103 21 103 km3 or 0 43 0 06 m of potential sea level rise

elevation change and ice flow at horseshoe valley patriot hills west antarctica patriot hills is located at 80 18 s 81 22 w at the southernmost end of the heritage range ellsworth mountains west antarctica a comparison of glacier elevation data and ice velocities obtained by the differential global positioning system in the period 1996 97 is presented ablation accumulation rates measured at a network of stakes in horseshoe valley show average accumulation of 70 kg m 2 a 1 in the central part of the valley and a maximum ablation of 170 kg m 2 a 1 at the edge of the blue ice area close to patriot hills changes in the surface elevation of the glacier measured at 81 stakes in the period 1995 97 show a mean thickening of 0 43 0 42 m a 1 which considering the uncertainties indicates that the ice sheet around patriot hills is in near steady state surface velocities in combination with ice thicknesses obtained by ground based radio echo sounding are used to compute the ice flux across the horseshoe valley transect a total outflow of 0 44 0 08 km 3 a 1 is obtained considering a catchment area for horseshoe valley of 1087 km 2 upstream from the flow transect and a net accumulation rate of 100 kg m 2 a 1 a total input of 0 11 0 04 km 3 a 1 by snow accumulation is obtained accepting a near equilibrium condition for the ice sheet the flux difference i e 0 33 km 3 a 1 must be supplied by flow from the inland ice sheet through ice cliffs located in mountain gaps in the heritage range if horseshoe valley is not in steady state but is thickening the positive mass balance could be due to increased snow accumulation or enhanced ice flow from the interior of the ice sheet new data are needed to elucidate this

towards bedmap himalayas development of an airborne ice sounding radar for glacier thickness surveys in high mountain asia the thickness of glaciers in high mountain asia hma is critical in determining when the ice reserve will be lost as these glaciers thin but is remarkably poorly known because very few measurements have been made through a series of ground based and airborne field tests we have adapted a low frequency ice penetrating radar developed originally for antarctic over snow surveys for deployment as a helicopter borne system to increase the number of measurements the manoeuvrability provided by helicopters and the ability of our system to detect glacier beds through thick dirty temperate ice makes it well suited to increase greatly the sample of measurements available for calibrating ice thickness models on the regional and global scale the bedmap himalayas radar survey system can reduce the uncertainty in present day ice volumes and therefore in projections of when hma s river catchments will lose this hydrological buffer against drought

polyorogenic 40 ar 39 ar mineral age record in the seve and koli nappes of the gaddede area northwestern jamtland central scandinavian caledonides in the scandinavian caledonides eugeoclinal terranes represented in the koli nappes were thrust 500 km onto the baltoscandian platform during the early to middle paleozoic immediately underlying thrust sheets of the seve nappe complex are suspected to have been derived from the outer margin of continent baltica contrasting tectonothermal histories are recorded in seve and koli nappes exposed in the gad dede area northern jamtland county sweden eclogite bearing seve rocks underwent an initial amphibolite grade regional metamorphism smi with different structural units experiencing contrasting high to intermediate pressure conditions subsequent ductile imbrication sm2 of high and intermediate pressure structural units occurred prior to 460 470 ma cooling through temperatures required for intracrystalline retention of argon in hornblende a later thermal overprint sm3 everywhere rejuvenated seve biotite and muscovite and locally hornblende argon systems at 430 pm 5 ma 40 ar 39 ar plate

till beneath ice stream b 1 properties derived from seismic travel times seismic experiments conducted on ice stream b part of the marine ice sheet of west antarctica show a meters thick layer immediately beneath the 1000 m thick ice a seismic experiment consisting of wide angle reflection profiling along a line parallel to ice stream flow was conducted to determine the properties of this layer inversion of seismic travel times yields a compressional wave speed of less than 1700 m s 1 and a shear wave speed less than 160 m s 1 for the layer these very low wave speeds imply that the material in the layer is highly porous and is saturated with water at a high pore pressure based on wave speeds in other saturated unconsolidated sediments we believe that a porosity substantially greater than 0 32 probably around 0 4 and an excess of overburden pressure over pore pressure of only 50 kpa 0 5 bar characterize the layer at this location

stable carbon isotopes of wood a clue to palaeoclimate abstract detailed stable carbon isotope and molecular investigations were undertaken on a number of archaeological and fossil wood specimens to provide insights into their use as rigorous independent palaeoclimatic and palaeoenvironmental parameters the isotope data revealed large differences amongst the material with the oldest specimens being least depleted in 13 c although natural variation could account for some of the observed differences the isotope values of the archaeological and tertiary specimens are most probably related to the absolute abundance of polysaccharides present and the degree of lignin alteration the molecular data based on pyrolysis of the antarctic cretaceous conifer specimens revealed only transformed lignin with virtually no intact lignin building blocks 2 methoxyphenols preserved and no evidence of polysaccharides this degree of chemical alteration is suggested here to be one of the main causes for the 13 c enriched values of these conifer specimens these results show the importance of combining detailed molecular information on individual wood components with stable carbon isotope data for palaeoclimatic and palaeoenvironmental studies

excess40ar in metamorphic rocks from broken hill new south wales implications for40ar 39ar age spectra and the thermal history of the region 40ar 39ar age spectrum analyses of samples from broken hill new south wales indicate that the region has experienced a complex thermal history following high grade metamorphism 1660 ma ago the terrain cooled slowly 3 c ma 1 until about 1570 ma ago when the temperature fell below about 500 c following granitoid emplacement 1500 ma ago the region remained relatively cold until affected by a thermal pulse 520 40ma ago causing temperatures to rise to 350 c in some places during this event accumulated40ar was released from minerals causing a significant ar partial pressure to develop laboratory ar solubility data combined with the40ar 39ar age spectra gives a local estimate of this partial pressure of 10 4atm the region finally cooled below 100 c about 280 ma ago 40ar 39ar age spectrum analyses of hornblende plagioclase and clinopyroxene containing excess40ar are characterized by saddle shaped age spectra detailed analysis of plagioclase samples reveals a complex diffusion behaviour which is controlled by exsolution structures this effect in conjunction with the presumed different lattice occupancy of excess40ar with respect to radiogenic40ar appears to be responsible for the saddle shaped age spectra

the microstructure of polar ice part i highlights from ice core research polar ice sheets play a fundamental role in earth s climate system by interacting actively and passively with the environment active interactions include the creeping flow of ice and its effects on polar geomorphology global sea level ocean and atmospheric circulation and so on passive interactions are mainly established by the formation of climate records within the ice in form of air bubbles dust particles salt microinclusions and other derivatives of airborne impurities buried by recurrent snowfalls for a half century scientists have been drilling deep ice cores in antarctica and greenland for studying such records which can go back to around a million years experience shows however that the ice sheet flow generally disrupts the stratigraphy of the bottom part of deep ice cores destroying the integrity of the oldest records for all these reasons glaciologists have been studying the microstructure of polar ice cores for decades in order to understand the genesis and fate of ice core climate records as well as to learn more about the physical properties of polar ice aiming at better climate record interpretations and ever more precise models of ice sheet dynamics in this part i we review the main difficulties and advances in deep ice core drilling in antarctica and greenland together with the major contributions of deep ice coring to the research on natural ice microstructures in particular we discuss in detail the microstructural findings from camp century byrd dye 3 grip gisp2 northgrip vostok dome c edml and dome fuji besides commenting also on the earlier results of some pioneering ventures like the jungfraujoch expedition and the norwegian british swedish antarctic expedition among others in the companion part ii of this work faria et al 2014 the review proceeds with a survey of the state of the art understanding of natural ice microstructures and some exciting prospects in this field of research

airborne radar sounder for temperate ice initial results from patagonia we describe the development of a low frequency airborne radar specifically designed for the sounding of temperate ice the system operates at a central frequency of 1 mhz and consists of an impulse transmitter with an output voltage up to 5000 v and a digital receiver with a maximum gain of 80 db the radar was deployed on board a casa 212 aircraft which also carries a laser altimeter an inertial navigation system a digital camera and a gps receiver a description of the radar system is provided as well as preliminary results obtained at glaciar tyndall campo de hielo sur southern patagonia icefield where an ice depth of 670 m was reached

basal conditions at engabreen norway inferred from surface measurements and inverse modelling engabreen is an outlet glacier of the svartisen ice cap located in northern norway it is a unique glacier due to the svartisen subglacial laboratory which allows direct access to the glacier bed in this study we combine both sub and supraglacial observations with ice flow modelling in order to investigate conditions at the bed of engabreen both spatially and temporally we use the full stokes model elmer ice and satellite based surface velocity maps from 2010 and 2014 to infer patterns of basal friction direct measurements of basal sliding and deformation of lower layers of the ice are used to adjust the ice viscosity and provide essential input to the setup of our model and influence the interpretation of the results we find a clear seasonal cycle in the subglacial conditions at the higher elevation region of the study area and discuss this in relation to the subglacial hydrological system our results also reveal an area with an overdeepening where basal friction is significantly lower than elsewhere on the glacier all year round we attribute this to either water pooling at the base or saturated sediments and increased strain heating at this location which softens the ice further

recognition of extraneous argon components through incremental release 40ar39ar analysis of biotite and hornblende across the grenvillian metamorphic gradient in southwestern labrador 40ar39ar incremental release ages have been determined for 15 hornblende and 20 biotite concentrates separated from rocks collected across the garnet and kyanite zones of grenvillian metamorphism in southwestern labrador most hornblende spectra from the kyanite zone are slightly discordant with low temperature increments yielding ages older than the ca 1000 ma date suggested for culmination of grenvillian metamorphism in the area however all the hornblende concentrates record well defined plateau ages these range from 968 to 905 ma across the kyanite zone and date times of diachronous post metamorphic cooling the discordant spectra are interpreted to result from low temperature liberation of excess 40ar components from grain margins two hornblende concentrates from the garnet zone display very discordant spectra total gas ages of 2100 and 3017 ma in which incremental dates systematically decrease during analysis this pattern of discordance suggests that excess argon components are inhomogeneously distributed throughout these hornblende grains most biotites from the garnet and kyanite zones record total gas or plateau ages in excess of 1000 ma 2066 857 ma reflecting the widespread presence of excess argon components because most of the 40ar39ar age spectra are internally concordant the ratios of excess 40ar relative to radiogenic 40ar must have been uniform in the various gas fractions liberated from each sample this is also reflected in the inability of isotope correlation diagrams to differentiate between excess radiogenic and atmospheric argon components the biotite total gas or plateau dates show marked local variation this is interpreted to indicate that the biotite grains were in contact with a post metamorphic intergranular vapor phase that was characterized by large and variable 40ar36ar ratios such ratios most likely resulted from widespread diffusion of the argon liberated from adjacent archean basement gneisses during the grenvillian metamorphic overprint

melt regimes stratigraphy flow dynamics and glaciochemistry of three glaciers in the alaska range we used ground penetrating radar gpr gps and glaciochemistry to evaluate melt regimes and ice depths important variables for mass balance and ice volume studies of upper yentna glacier upper kahiltna glacier and the mount hunter ice divide alaska we show the wet percolation and dry snow zones located below 2700ma s l at 2700 to 3900ma s l and above 3900ma s l respectively we successfully imaged glacier ice depths upwards of 480m using 40 100mhz gpr frequencies this depth is nearly double previous depth measurements reached using mid frequency gpr systems on temperate glaciers few holocene length climate records are available in alaska hence we also assess stratigraphy and flow dynamics at each study site as a potential ice core location ice layers in shallow firn cores and attenuated glaciochemical signals or lacking strata in gpr profiles collected on upper yentna glacier suggest that regions below 2800ma s l are inappropriate for paleoclimate studies because of chemical diffusion through melt flow complexities on kahiltna glacier preclude ice core climate studies minimal signs of melt or deformation and depth age model estimates suggesting 4815years of ice on the mount hunter ice divide 3912ma s l make it a suitable holocene age ice core location

vegetation history inferred from pollen in late quaternary faecal deposits hyraceum in the cape winter rain region and its bearing on past climates in south africa abstract pollen analysis shed light on vegetation community structure over the last 23 000 year in the western cape the pollen from dated hyrax faecal accumulations hyraceum relates to the evolution of climate and contributes to proxy records in southern africa principal components analyses of the pollen data and 13c values of the hyrax dung samples show millennial and shorter scale temperature moisture and seasonality variations in the winter rain region the moisture availability at times do not parallel that in previously studied proxy records in the summer rain region showing an asynchronous moist event in the early holocene and drier conditions in the middle holocene anomalies in climate between the two regions may depend on the degree of northward or southward shifting of winter and summer rain circulation systems scenarios with winter rain or cool growing seasons mostly typify the dung sequence but do not exclude the possibility of southward displacement of the westerly belt under precessional strength with slight summer rain increases during the last glacial maximum limited southward displacement is also possible during the mid holocene

ice thickness measurements of taku glacier alaska u s a and their relevance to its recent behavior using radio echo soundings and seismic reflections we measured cross sections of taku glacier near juneau alaska to resolve inconsistencies in previous measurements and to understand better the glacier s dynamics the maximum thickness is about 1477 m and the minimum bed elevation is about 600 m below sea level which establishes taku glacier as the thickest and deepest temperate glacier yet measured our data indicate that during the 19th century the terminus of taku glacier may have begun its rapid advance at a position where the ice bed was greater than 300 m below sea level and more than 25 km from the inland end of its submarine trough this behavior is uncharacteristic of temperate tide water glaciers the glacier which no longer calves has eroded a sediment layer 100 m thick since 1890 at an average rate of about 3 m a 1 since 1948 this high erosion rate retards advance by entrenching the glacier into the terminal moraine calculations based on ice deformation theory indicate significant basal ice motion near the terminus and high basal shear stress 140 220 kpa along much of its length estimated differences between ice flux and balance flux are consistent with observed thickening and positive net mass balance these data indicate that ice volume is increasing and that further advance is likely

mineral age record of a polyorogenic evolution within the seve and koli nappes trondelag norway abstract in the central scandinavian caledonides eugeoclinal terranes represented in the koli nappes were thrust 500 km onto the baltoscandian platform during the early to middle paleozoic immediately underlying thrust sheets of the seve nappe complex are suspected to have been derived from the outer margin of continent baltica hornblende within amphibolite at one locality within westernmost exposures of seve nappe units in trandelag norway displays an internally discordant 40 ar 39 ar age spectrum which suggests a polyphase thermal evolution including 1 1 initial post metamorphic cooling through argon retention temperatures at c 475 480 ma 2 2 partial rejuvenation during a silurian c 400 425 ma thermal overprint muscovite within the exposure was more extensively rejuvenated during the silurian overprint at twelve other trandelag sample locations hornblende muscovite and biotite within both the seve and koli nappe complexes record post metamorphic cooling ages between 420 and 435 ma and display no direct evidence of a pre silurian thermal record however the widespread occurrence of intracrystalline extraneous argon components and textural complexities clearly point toward a pre silurian tectonothermal history comparison with 40 ar 39 ar mineral ages reported elsewhere in the central scandinavian caledonides suggests a polyorogenic evolution consisting of 1 1 variable high pressure metamorphism of distal baltoscandian miogeoclinal sequences during entrainment in an accretionary wedge which developed in the late cambrian early ordovician over a west dipping subduction zone related arc volcanic activity occurred in more outboard western sectors 2 2 ductile imbrication of high and intermediate pressure sequences within the accretionary wedge diachronous cooling and or chronologically distinct tectonic episodes are indicated throughout the early and middle ordovician 3 3 ultimate accretion of a variety of eugeoclinal terranes along the baltica continental margin 4 4 imbrication and metamorphism of the eugeoclinal terranes and previously deformed portions of the miogeocline during eastward translation onto the baltoscandian platform in the silurian crystalline baltica basement and overlying structural cover units were depressed to significant crustal depths during eastward nappe transport with resultant formation of high temperature eclogues previously reported crystallization ages of c 425 ma suggest that the eclogites formed at approximately the same time as minerals within the superencumbent nappe units cooled through argon closure temperatures following eastward nappe transport the basement experienced rapid uplift and resultant adiabatic decompression this was followed by rapid cooling through argon retention temperatures at 390 400 ma

fast tidewater glaciers some iceberg calving outlet glaciers flow continuously at speeds normally associated with surging glaciers arid exhibit dramatic instability scenarios related to those suggested for marine ice sheets no temperate tidewater glaciers are known to have floating termini but many polar and subpolar tidewater glaciers do the fast flow of temperate calving glaciers is almost entirely due to basal sliding and appears to be a function of the effective pressure on the bed which may approach zero and the longitudinal back stress on the terminus the terminus boundary condition the calving relation is imperfectly known yet is vital to the dynamics of these glaciers calving relations for grounded tidewater glaciers have been suggested on empirical grounds but have not been rigorously tested the calving relations for floating termini are virtually unknown this together with the imperfect understanding of basal sliding inhibits confidence in our understanding of the stability of these glaciers columbia glacier alaska is an instructive example because observations have been made on the major changes in its geometry calving rate and dynamics that have occurred in less than 10 years the calving flux has increased more rapidly than the glacier flux causing thinning and retreat as a result the ice velocity has increased markedly the short term velocity changes relate to changes in back pressure ice recession tidal changes and the flux of water injected to the bed these results have relevance to the mechanisms of basal sliding glacier surges and the stability of marine ice streams

prospects for reconstruction of seasonal environment from tree ring δ13c baseline findings from the great lakes area usa abstract plant 13 c and discrimination 13 c air 13 c plant embody ecophysiological response to environmental conditions influencing rates of carbon fixation and stomatal conductance this study scrutinizes the seasonal variation of 13 c and in growth rings developed in 1990 as represented in trees of 11 species at three sites along a 5 latitude transect in illinois and wisconsin usa radial stem xylem growth of the trees was monitored with monthly punch cores and the resulting growth curves precisely identified the growth period represented in the five segments into which each growth ring was subdivided seasonal 13 c variation of cellulose was usually 1 1 5 and the seasonal patterns were similar among angiosperm and conifer trees at a site with angiosperms generally 13 c depleted by 0 5 1 5 seasonal 13 c and patterns was different among sites however and regression with several environmental parameters revealed most frequent significant correlation with soil moisture palmer drought severity index pdsi the site averaged seasonal patterns track each of their divergent local seasonal drought index chronologies very well even when isotopic curves of the different trees are simply averaged without adjustment for different growth rates seasonal tree ring 13 c analysis is affirmed as a valuable method for assessing seasonal moisture status furthermore results favor successful extension to ancient tree rings where different species and slope aspects may be represented in wood samples at a collection site and where rates of ring development and seasonal 13 c air are not likely to be known

glacial erosion status and outlook glacier erosion rates range across orders of magnitude and much of this variation cannot be attributed to basal sliding rates subglacial till acts as lubricating fault gouge or sawdust and must be removed for rapid subglacial bedrock erosion such erosion occurs especially where and when moulin fed streams access the bed and are unconstrained by supercooling or other processes streams also may directly erode bedrock likely with strong time evolution erosion is primarily by quarrying aided by strong fluctuations in the water system driven by variable surface melt and by subglacial earthquakes debris bed friction significantly affects abrasion quarrying and general glacier flow frost heave drives cirque headwall erosion as winter cold air enters bergschrunds creating temperature gradients to drive water flow along premelted films to growing ice lenses that fracture rock and the glacier removes the resulting blocks recent subglacial bedrock erosion and sediment flux are in many cases much higher than long term averages over glacial cycles evolution of glacial valley form feeds back strongly on erosion and deposition most of this is poorly quantified with parts open to argument glacial erosion and interactions are important to tectonic and volcanic processes as well as climate and biogeochemical fluxes motivating vigorous research

taku glacier alaska u s a on the move again active deformation of proglacial sediments taku glacier is one of the few glaciers in alaska u s a that has advanced over the last century 7 km since 1890 this advance slowed substantially during the past decade but in summer 2001 the glacier terminus began to readvance at a rate of 30 cm d 1 the advance produced dramatic proglacial sediment deformation up to 200 m in from of the terminus two to three large bulges and several secondary bulges developed in the proglacial sediments as a result of glacial compression along a 1 km wide portion of the terminus the bulge nearest the terminus was 10 m high and 65 m wide the middle bulge 7 m high advanced at 15 cm d 1 and the distal bulge 3 m high and 50 m wide at 9 cm d 1 crenulations and prominent fractures developed in the overlying vegetation layer the frontal lobes of the bulges were steep and overlaid a shear zonc where sediments were being thrust up and over the ground surface ice proximal push moraines 1 10 m high formed along much of the 9 km wide terminus although deformation was minimal at some locations

40 ar 39 ar mineral age record of early caledonian tectonothermal activity in the baltoscandian miogeocline central scandinavia in central portions of the scandinavian caledonides greenschist facies volcanosedimentary successions within the koeli nappe complex have been thrust several hundred kilometers eastward onto the baltoscandian platform these were derived from eugeoclinal terranes situated outboard west of the baltica continent during the early paleozoic the koeli nappe complex is tectonically underlain by higher grade units within the seve nappe complex these are composed of amphibolite and granulite facies rocks and locally contain eclogites the seve nappes tectonically separate koeli units from structurally lower allochthons derived from more inboard environments along the baltoscandian miogeocline previous mineral isotopic age determinations from seve and koeli units have been in the 430 to 390 ma range and have been interpreted to presumably date cooling following scandian middle silurian to early devonian metamorphism however incremental release sup 40 ar sup 39 ar dates recorded by minerals within some of the koeli and seve nappes exposed in jaemtland sweden taennforsen and are districts provide evidence of earlier tectonothermal activity hornblendes from the seve and koeli nappe complexes display variably discordant age spectra as a result of low temperature experimental evolution of loosely bound extraneous argon components however in most analyses plateau ages of 510 to 475 ma koeli and 465 to 455more ma seve are defined in contrast muscovite and biotite from all tectonic units record scandian cooling ages between 245 and 410 ma the older events recorded by hornblende within these seve and koeli units are evidence of early caledonian tectonothermal activity and subsequent diachronous cooling during the early middle ordovician less

geochronology of the swift current granite and host volcanic rocks of the love cove group southwestern avalon zone newfoundland evidence of a late proterozoic volcanic subvolcanic association zircon fractions from the variably deformed and metamorphosed swift current granite and host volcanic rocks of the love cove group record individually discordant u pb ages with well defined upper c

the middle to late devonian hoybakken detachment central norway 40ar 39ar evidence for prolonged late post scandian extension and uplift the regionally significant 0 5 2 km thick hoybakken detachment in central norway bounds the southern margin of the central norway basement window and exhibits a well developed top to the wsw fabric characteristic of late scandian devonian ductile extension 40 ar 39 ar data obtained from hornblende mica and k feldspar mineral separates of rocks collected in a transect through the hoybakken detachment yield well defined plateau and isochron mineral ages early devonian exhumation and cooling of the hoybakken detachment footwall is recorded by hornblende ages of 400 ma and mica ages of 390 ma the mylonitic fabric overlying the footwall records younger middle devonian mica crystallization ages of 384 381 ma that are among the youngest extensional ductile fabrics dated in the caledonides and suggest prolonged extensional activity on the hoybakken detachment after inferred cessation of ductile extension at 381 ma the rate of uplift and cooling was reduced and the footwall records late devonian to early carboniferous k feldspar ages of 371 356 ma prolonged extensional activity at hoybakken is compatible with recent u pb ages of deformed titanite crystals and established rb sr ages of white mica in shear related pegmatites both from the southwestern part of the fosen peninsula and 40 ar 39 ar ages of syn tectonic mica overgrowth from the adjacent hitra snasa fault together these ages suggest the onset of ductile extension soon after 401 ma and with the middle devonian crystallization ages determined here suggest that ductile extension on the hoybakken detachment had a duration of 11 20 ma the youngest age of 320 ma was obtained from a k feldspar in a cataclastic granite of the hoybakken detachment s hangingwall and is considered to date a phase of post scandian brittle deformation that overprinted the mylonitic shear fabric

is cellulose extraction necessary for developing stable carbon and oxygen isotopes chronologies from callitris glaucophylla abstract we examined the necessity of extracting cellulose for the development of stable carbon and oxygen isotope chronologies from callitris glaucophylla j thompson and l a s johnson cupressaceae we compared relationships among isotopes of whole wood cellulose and climate for the period 1979 1999 and using a moving interval technique with a 10 year window isotopes of whole wood and cellulose were significantly correlated and had similar relationships with climate when considered over the entire period in general variation in 13 c and 18 o was related to summer temperature relative humidity and rainfall however 13 c and 18 o of whole wood generally exhibited weaker and more variable correlations with climate through time than cellulose in addition isotopes of whole wood did not deviate from 1979 to 1999 mean values in the same way as isotopes of cellulose the instability of whole wood climate relationships may be due to the inclusion in whole wood of a climate signal from lignin that is more variable between tree rings than cellulose overall it appears that c glaucophylla at least whole wood does not record climate in the same way as cellulose and stable isotopes of cellulose provide a more temporally stable proxy of past climate we suggest that when developing isotope chronologies for other species the suitability of whole wood vs cellulose as a proxy for climate should be assessed with consideration of the temporal stability of their relationship with climate

time series analyses of tree ring chronologies from pacific north america evidence for sub century climate oscillations abstract tree ring width chronologies from the west coast of north america were obtained from on line data archives maintained by the national oceanic and atmospheric administration noaa data covered the period 1650 1983 for trees sampled at 43 sites between dawson creek british columbia 55 n and yosemite park ca 37 n these time series were analyzed using fourier transformation methods spyglass transform software allowed the resulting power spectra to be stacked and compared based on characteristics such as topography and continentality latitude and species ecological niche results suggested that several regular or quasi regular cycles are occurring over various time periods there are some similarities though not an exact match with el nino periodicities noted by earlier authors these patterns appear to be widespread affecting trees at various elevations and distances from the coast and from different species a separate analysis of the oldest trees revealed sub century cycles in particular the longer fluctuations at 50 65 years are consistent with recent findings on north pacific climate by other authors a euclidean cluster analysis of individual years identified unusual year groupings between 1924 1946 a period associated with positive temperature anomalies and generally higher precipitation these findings appear to be consistent with other basin scale climate cycles like the southern oscillation and the recently proposed pacific interdecadal oscillation pdo