late proterozoic lavas of the central arabian shield evolution of an ancient volcanic arc system a petrological assessment of 11 volcano sedimentary belts in the central arabian shield cas using 118 new analyses is presented the same samples have been used in a rb sr dating programme also reported in this volume the oldest volcano sedimentary belts sequence c 900 ma are chemically immature bimodal suites of low k tholeiites and sodic dacite rhyolite depleted in lithophile elements these lavas have chemical characteristics similar to immature island arcs such as the tonga kermadee and lesser antilles arcs younger lavas of sequence b 900 700 ma are slightly more mature in composition being predominantly calc alkaline and low k arc tholeiite series with higher lithophile element contents they are comparable with pacific island are averages the youngest voluminous lavas sequence a 700 570 ma are generally calc alkaline or high k calc alkaline series lavas with moderately high lithophile element abundances they are comparable to volcanic arcs such as central america and indonesia which are transitional between island arcs and continental margin volcanic arcs the cratonization process in the cas thus involved the superimposition of three volcano sedimentary sequences formed in progressively maturing volcanic arcs early formed immature island arcs were succeeded by chemically more mature island arc deposits and then by deposits formed in volcanic arc s transitional between island arcs and continental margins the evolution ceased at this stage and probably did not advance to the equivalent of an andean continental margin

wollastonite and scapolite in precambrian calc silicate granulites from australia and antarctica abstract scapolite wollastonite calcite diopside grossular andradite garnet and sphene occur in calc silicate rocks in the granulite terrain of the arunta block central australia this assemblage buffers the co2 activity at a low value so that any coexisting fluid phase must be h2o rich and co2 poor xco2 0 2 0 3 in contrast the h2o activity in the surrounding felsic and mafic granulites was low thus fluid activities during granulite facies metamorphism were locally buffered in various rock units and fluid flow appears to have been restricted or fluid may have been absent late retrograde rims of garnet and garnet quartz separate phases formed in the high grade stage formation of these rims would have required either an influx of water rich fluid or a decrease in pressure evidence from the surrounding granulites shows that in one locality the calc silicate rocks had undergone late isobaric hydration in another locality minor uplift had occurred soon after peak p t conditions in both scapolite had partly broken down to plagioclase calite a calc silicate rock from the granulite terrain of enderby land antarctica contains scapolite wollastonite calcite diopside quartz and sphene this assemblage also indicates low co2 activities in this rock wollastonite has broken down to calcite quartz to indicate isobaric cooling without influx of hydrous fluid

distinct patterns of seasonal greenland glacier velocity predicting greenland ice sheet mass loss due to ice dynamics requires a complete understanding of spatiotemporal velocity fluctuations and related control mechanisms we present a 5 year record of seasonal velocity measurements for 55 marine terminating glaciers distributed around the ice sheet margin along with ice front position and runoff data sets for each glacier among glaciers with substantial speed variations we find three distinct seasonal velocity patterns one pattern indicates relatively high glacier sensitivity to ice front position the other two patterns are more prevalent and appear to be meltwater controlled these patterns reveal differences in which some subglacial systems likely transition seasonally from inefficient distributed hydrologic networks to efficient channelized drainage while others do not the difference may be determined by meltwater availability which in some regions may be influenced by perennial firn aquifers our results highlight the need to understand subglacial meltwater availability on an ice sheet wide scale to predict future dynamic changes

dynamic and thermal responses of the kuroshio to typhoon megi 2004 relatively weak hurricane induced cooling 1 c is often observed in the loop current while observed sea surface temperature sst cooling is much stronger in the kuroshio this was previously attributed to strong advection effects by the loop current based on a budget analysis this study quantitatively diagnoses the dynamic and thermal responses of the kuroshio to typhoon megi and four additional tropical cyclones tcs which produce up to 3 c sst cooling within the kuroshio itself the results show that the surface thermal response of the kuroshio is a wind induced temperature cooling primarily due to vertical mixing up to 96 the dynamic response of the kuroshio depends not only on tc conditions intensity and wind direction but also on prestorm ocean conditions e g ocean mixed layer depth baroclinicity and current velocity differently from the open ocean where the ocean gains kinetic energy mainly from wind stress work the kuroshio can obtain greater kinetic energy from its baroclinic pressure work especially in the upper ocean the strong sst cooling observed in the kuroshio region is therefore likely associated with the kinetic energy extracted from the kuroshio baroclinic potential energy which greatly enhances local vertical mixing

pan african volcanism petrology and geochemistry of the dokhan volcanic suite in the northern nubian shield the late proterozoic dokhan volcanic suite 620 ma of the northern nubian shield is the product of late pan african volcanism the suite covers the entire spectrum from basalt to high silica rhyolite and occurs as two units a dark coloured unit containing basalt andesite dacite and a light coloured unit encompassing dacite rhyodacite rhyolite the latter unit is made up largely of ash flow tuffs and ign imbrites that are locally interstratified with basalt and andesite lava flows the suite forms a continuum in composition with a wide range of si0 2 48 77 wt cao 0 1 8 9 wt sr 81 906 ppm zr 85 340 ppm as well as most other elements and is moderately enriched in incompatible elements including rare earth elements ree the suite exhibits fractionated subparallel ree patterns that are similar overall to andean andesites and ignimbrites well defined major and trace element trends and fractionated ree profiles are consistent with a fractionated basalt to rhyolite calc alkaline magma series it is a typical calc alka line orogenic complex and exhibits mineralogical geochemical traits of arc related volcanism the suite neither resembles products of extensional nor transitional tectonic regimes as previously thought but was produced in a subduction related tectonic environment the mafic nature of the least evolved rocks of the suite along with its relatively low initial 87 sr 86 sr ratio 0 7039 are considered to indicate a mantle source a mantle derived basaltic magma fractionated with amphibole and plagioclase dominating the fractionating assemblage to produce the more felsic varieties as suggested by major and trace element fractionation modelling

nd and sr isotopic systematics of central australian granulites chronology of crustal development and constraints on the evolution of lower continental crust nd and sr isotopic data are reported for a granulite terrain in the proterozoic arunta block of central australia sm nd data from a wide range of rock types define a crust formation age of 2 070 125 ma and provide further evidence for voluminous crustal growth in the proterozoic an nd value of 1 5 0 8 indicates a depleted mantle source for this crustal segment and there is no evidence for a large component of significantly older sialic crust field relationships geochemistry and rb sr data for mafic and felsic granulites indicate that intracrustal differentiation and polyphase deformation were followed by granulite facies metamorphism rb depletion at 1 800 ma rb sr data for strongly retrogressed granulites define an age of 1 700 ma which is interpreted as the time of retrograde biotite growth partial melting at the presently exposed crustal level and anatexis at deeper crustal levels were broadly coeval with the retrograde metamorphism sm nd and rb sr isotopic systematics of minerals indicate that the terrain cooled slowly did not experience significant uplift until 1 000 ma and remained at temperatures above 320 c until the late palaeozoic the mineral data are consistent with geological relationships and petrological evidence for a prolonged period of isobaric cooling followed by uplift late in the metamorphic evolution of the terrain the granulite protoliths appear to have formed in a rift which closed within 280 ma of initial separation deformation and granulite facies metamorphism at 1 800 ma are interpreted to be a consequence of collision between the continental blocks which defined the rift regional retrogression and granitoid magmatism at 1 700 ma are attributed to underthrusting of the granulites by lower grade rocks in the final stages of collision subsequent events in the cooling and uplift history appear to have been controlled by the presence of long lived major faults in the crust and a prolonged history of episodic compression in the continental lithosphere the results of this study suggest that granulite terrains in general cannot be equated with lower continental crust but instead represent assemblages of mainly supracrustal rocks which in some instances have been involved in major collision events

dynamics of surge type glaciers in west kunlun shan northwestern tibet here we examine 31 glaciers in the west kunlun shan of the northwestern tibetan plateau and identify 9 as surge type the method is based on satellite synthetic aperture radar and landsat optical images the former going back to 1992 the latter to 1972 to identify surge type glaciers we consider temporal changes in velocity changes in glacier terminus position propagation of a surge bulge presence of looped and or contoured medial moraines and extensive crevassing other than the nine surge type glaciers we identify two that have likely surged and six that may be surge type but no glacier surges more than once during the observation period meaning that the recurrence interval exceeds 42 years in addition we examine the evolution of the surface velocities at two surging glaciers with the unprecedented temporal resolution of down to 11 days over 7 years the results show clear seasonal modulations by as much as 200 in early winter against those in early summer this seasonal modulation in surface velocity suggests the presence of surface meltwater that reroutes through the englacial and subglacial drainage systems thus our findings suggest that the hydrological processes originating in the surface meltwater play an important role in maintaining the yearlong active surging phase

progress on upwelling studies in the china seas east asian marginal seas surrounding china exhibit rich ocean upwelling mostly in response to the southwesterly summer monsoon upwelling in the china seas namely the south china sea the taiwan strait the east china sea the yellow sea and the bohai sea has become increasingly important because the potential changes in the upwelling may have dramatic ecosystem socioeconomic and climate impacts this paper reviews the progress of upwelling studies in the china seas since the year 2000 by presenting the principal characteristics and new understanding of 12 major upwelling regions in the china seas upwelling exhibits long term variability at intraseasonal to multi decadal scales as well as short term variability frequently caused by tropical cyclones it is also associated with the el nino southern oscillation local environmental variation and biogeochemical factors the coastal upwelling around hainan island and the upwelling or cold dome northeast of taiwan island are specifically highlighted because they have attracted great interest for decades this paper summarizes upwelling mechanisms in terms of wind topography tide stratification and background flow with applications mostly to the china seas finally we propose some topics for future upwelling research i e potential intensification of coastal upwelling under global climate change downwelling intrusion of upwelling into coastal embayments and the influence of upwelling on fishery and biogeochemical processes

climatic and geometric controls on the global distribution of surge type glaciers implications for a unifying model of surging financial support was provided by the conocophillips lundin northern area program project crios

fast retreat of zachariae isstrom northeast greenland after 8 years of decay of its ice shelf zachariae isstrom a major glacier of northeast greenland that holds a 0 5 meter sea level rise equivalent entered a phase of accelerated retreat in fall 2012 the acceleration rate of its ice velocity tripled melting of its residual ice shelf and thinning of its grounded portion doubled and calving is now occurring at its grounding line warmer air and ocean temperatures have caused the glacier to detach from a stabilizing sill and retreat rapidly along a downward sloping marine based bed its equal ice volume neighbor nioghalvfjerdsfjorden is also melting rapidly but retreating slowly along an upward sloping bed the destabilization of this marine based sector will increase sea level rise from the greenland ice sheet for decades to come

tidewater glacier surges initiated at the terminus terrasar x data were provided by dlr project oce1503 and funded by the conoco phillips lundin northern area program through the crios project calving rates and impact on sea level c n acknowledges funding from european union erc grant 320816 and esa project glaciers cci 4000109873 14 i nb

age of feiran basement rocks sinai implications for late precambrian crustal evolution in the northern arabian nubian shield basement exposed on the perimeter of the red sea was created during the pan african event at the end of the precambrian pre pan african crust in the northern part of this region has not yet been identified this paper reports the results of rb sr whole rock and u pb zircon dating of gneisses and related basement units from the wadi feiran area in the sinai peninsula where the existence of such older basement has previously been suggested a post tectonic extensional dyke gives a rb sr age of 591 9 ma with an initial 87 sr 86 sr ratio of 0 7034 0 0002 rb sr whole rock and thin slab dating of paragneisses gives ages of c 610 ma with an initial 87 sr 86 sr ratio of 0 7035 a u pb zircon age of 632 3 ma is interpreted as either the time of formation of these gneisses or the age of the crust sampled by protolith sediments granodiorite to the east gives a u pb zircon age of 782 7 ma and is interpreted as representing the westernmost extent of a 780 50 ma terrane that extends across sinai into jordan uplift and erosion of the 780 50 ma terrane supplied detritus to flanking terranes in n and se sinai this region thus acted as a foreland to the younger accretionary and extensional units to the south and west that were active later in the pan african event there is still no evidence for pre pan african basement in the precambrian units around the northern red sea east of the nile

neodymium isotopic constraints on the protolith ages of rocks involved in pan african tectonism in the mozambique belt of tanzania abstract nd isotopic data from samples collected across the tanzanian sector of the mozambique belt indicate that the bulk of the belt consists of early proterozoic crust which was tectonothermally reworked during pan african time the only evidence for younger crust is preserved in granulite complexes that are surrounded by older amphibolite facies gneisses the uniformity of crustal formation ages of the gneisses across most of the belt indicates that models explaining the mozambique belt as a tectonic collage of terranes with different pre pan african crustal histories are invalid

movement of the kuroshio axis to the northeast shelf of taiwan during typhoon events abstract we investigated the movement of the kuroshio axis on the northeast shelf of taiwan associated with the passage of typhoons using sea surface current data observed by the ocean radar system on yonaguni and ishigaki islands first we examined daily kuroshio axis variation on the northeast shelf of taiwan during typhoon events the ocean radar data showed that the kuroshio axis moved onto the shelf after passages of typhoons the kuroshio moved onto the shelf and stayed there after the passage of typhoon hai tang while the kuroshio maintained this pattern southerly wind blew continuously for 4 days the mean current speed northeast of taiwan after the typhoon s passage increased by 18 cm s 1 in addition the sea level difference between two satellite altimetry tracks east of taiwan increased by 14 4 cm these results suggest that coastal upwelling east of taiwan caused by the southerly wind generated an east west sea level difference that in turn generated a northward geostrophic current this current could have enhanced the kuroshio east of taiwan and pushed it onto the shelf

the duration of the active phase on surge type glaciers contrasts between svalbard and other regions many glaciers in svalbard and in other glacierized areas of the world are known to surge however the time series of observations required to assess the duration of fast motion is very restricted data on active phase duration in svalbard come from aerial photographs satellite imagery field surveys and airborne reconnaissance evidence on surge duration is available for eight svalbard ice masses varying from 3 to 1250 km 2 worldwide active phase duration is recorded for less than 50 glaciers few observations are available on high polar ice masses the duration of the active phase is significantly longer for svalbard glaciers than for surge type glaciers in other areas from which data are available in svalbard the active phase may last from 3 to 10 years by contrast a surge duration of 1 2 years is more typical of ice masses in northwest north america iceland and the pamirs ice velocities during the protracted active phase on svalbard glaciers are considerably lower than those for many surge type glaciers in these other regions mass is transferred down glacier more slowly but over a considerably longer period svalbard surge type glaciers do not exhibit the very abrupt termination of the active phase over periods of a few days observed for several alaskan glaciers the duration of the active phase in svalbard is not dependent on parameters related to glacier size the quiescent phase is also relatively long 50 500 years for svalbard ice masses detailed field monitoring of changing basal conditions through the surge cycle is required from surge type glaciers in svalbard in order to explain the significantly longer length of the active phase for glaciers in the archipelago which may also typify other high polar ice masses the finding that surge behaviour in the form of active phase duration shows systematic differences between different regions and their environments has important implications for understanding the processes responsible for glacier surges

crustal accretion in the pan african nd and sr isotope evidence from the arabian shield abstract nd and sr isotope determinations on late precambrian to early palaeozoic igneous and sedimentary rocks from the arabian shield are used to investigate the proportion of reworked older crust and the rate at which new crust was generated during the pan african event eight rb sr whole rock isochrons on igneous suites yield ages in the range 770 590 ma and initial 87 sr 86 sr ratios of 0 7038 0 7023 these data confirm that magmatism in this area was largely restricted to the period 850 550 ma and the initial ratios are sufficiently low to preclude significant contributions from a long lived upper crustal source the initial 143 nd 144 nd ratios of a variety of lithologies including several samples of possible basement are all higher than the contemporaneous values for chur e nd 1 6 to 6 9 suggesting that many were derived directly from the upper mantle and that any inferred crustal source regions for the remainder could not have separated from likely lree depleted mantle reservoirs before 1200 ma the arabian shield therefore provides an example of rapid crustal growth during the late proterozoic and contrasts with the damara intracratonic belt of namibia where nd and sr isotopes provide strong evidence for extensive reworking of older continental crust during the same period

island arc character and late precambrian age of volcanics at wadi shwas hijaz saudi arabia geochemical and sr and nd isotopic evidence abstract a summary description of two volcanic sequences named the surgah and the shwas formation situated in the wadi shwas area at long 42 0 lat 20 0 in the arabian shield is given major and trace element concentrations including ree abundances are presented as well as sr and some nd isotope results one sequence the surgah formation shows a tholeiitic differentiation trend from basaltic to rhyolitic rocks whereas the shwas formation has calc alkaline affinities both sequences have low concentrations of incompatible elements notably rb nb zr and ti the coexistence of a tholeiitic and a calc alkaline suite along with these low concentrations is strongly reminiscent of some present day island arc environments an rb sr errorchron age of 721 55ma was obtained on the surgah formation with high initial87sr 86sr ratios around 0 705 the rare earth abundances are overall very low and the patterns show a relative depletion of the light ree in the least evolved rocks indicating a relatively light ree depleted mantle source a time integrated light ree depleted source is also indicated by the fairly radiogenic143nd 144nd ratios end values around 8 the nd model age of source depletion tchurnd is around 2 2 ga

relating glacier mass balance to meteorological data using a seasonal sensitivity characteristic we propose to quantify the climate sensitivity of the mean specific balance b of a glacier by a seasonal sensitivity characteristic ssc the ssc gives the dependence of b on monthly anomalies in temperature and precipitation it is calculated from a mass balance model we show and discuss examples for franz josef glacier new zealand nigardsbreen norway hintereisferner austria peyto glacier canadian rockies abramov glacier kirghizstan and white glacier canadian arctic with regard to the climate sensitivity of b the sscs clearly show that summer temperature is the most important factor for glaciers in a dry climate for glaciers in a wetter climate spring and fall temperatures also make a significant contribution to the overall sensitivity the ssc is a 2 12 matrix multiplying it with monthly perturbations of temperature and precipitation for a particular year yields an estimate of the balance for that year we show that with this technique mass balance series can be re constructed from long meteorological records or from output of atmospheric models

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

bedmachine v3 complete bed topography and ocean bathymetry mapping of greenland from multibeam echo sounding combined with mass conservation greenland s bed topography is a primary control on ice flow grounding line migration calving dynamics and subglacial drainage moreover fjord bathymetry regulates the penetration of warm atlantic water aw that rapidly melts and undercuts greenland s marine terminating glaciers here we present a new compilation of greenland bed topography that assimilates seafloor bathymetry and ice thickness data through a mass conservation approach a new 150 m horizontal resolution bed topography bathymetric map of greenland is constructed with seamless transitions at the ice ocean interface yielding major improvements over previous data sets particularly in the marine terminating sectors of northwest and southeast greenland our map reveals that the total sea level potential of the greenland ice sheet is 7 42 0 05 m which is 7 cm greater than previous estimates furthermore it explains recent calving front response of numerous outlet glaciers and reveals new pathways by which aw can access glaciers with marine based basins thereby highlighting sectors of greenland that are most vulnerable to future oceanic forcing

the rb sr geochronological evolution of the ras gharib segment of the northern nubian shield rb sr whole rock isochron ages have been determined for six igneous rock suites from the ras gharib these represent all major crustal components of the northern nubian shield and are from oldest to youngest diorite tonalite extrusive rocks granodiorite adamellite and leucogranite muscovite trondhjemite orogenic pan african suites dyke swarms and anorogenic peralkaline granites the ages obtained are 881 58 ma 620 16 ma 552 7 ma 516 7 ma 493 7 ma and 476 2 ma the initial 87 sr 86 sr ratios of the pan african suites and the dykes are in the range 0 7039 to 0 7047 the initial ratio of the anorogenic peralkaline granites is 0 7110 0 0012 higher than any previously reported for igneous rocks from the egyptian belt the 493 7 ma age of the dyke swarms represents a younger limit for the pan african compression accretion event and an upper older limit for an extensional tectonic regime linked with this is the anorogenic peralkaline granite magmatism 476 2 ma which is the last manifestation of igneous activity in this region the low initial ratios of the pan african suites provide no support for the existence of an older archaen sialic continental crust in the region the anorogenic peralkaline granite with the high initial ratio was produced by partial melting of earlier pan african suites the age data are used to construct a tentative correlation scheme for shield rocks of egypt sudan and saudi arabia

a rift drift delamination model of continental evolution palaeozoic tectonic development of eastern australia the adelaide lachlan and new england fold belts of eastern australia record the continental growth of eastern gondwanaland during the palaeozoic the new england fold belt nefb represents a tectonic collage formed by subduction accretion during the late paleozoic but contains remnants of subduction related rocks that date from the cambrian the lachlan fold belt lfb developed inboard from the nefb initially as an amalgam of proterozoic continental and cambrian oceanic fragments that formed by rift and drift at the leading edge of eastern gondwanaland convergent tectonism at 500 ma welded the fragments to the craton and formed the adelaide fold belt oceanward dispersal of detritus across the lfb produced an overlap assemblage of quartzose ordovician turbidites and a new subduction zone developed at the eastern margin the tectonic setting was similar to the modern philippines plate of the western pacific behind the arc silurian devonian convergent tectonics converted the 1700 2000 km wide continental margin of the proto lfb into a 750 km wide thin skinned fold magmatic belt within 60 ma the driving force was delamination which produced a ubiquitous basaltic underplate that generated 1 regional low p metamorphism 2 local anticlockwise p t t paths and crustal scale isobaric cooling 3 voluminous syn to late tectonic granitoids emplaced at rates approximately twice that of modern arcs and 4 normal thickness crust despite an average of 60 shortening delamination occurred in two separate areas originally 1000 km apart first in the eastern then in the western part of the lfb the lfb and its northern counterpart the thomson fold belt represent approximately one fifth of the australian continent and evolved from dispersed fragments into stable continental crust in 300 ma such rapid growth rates are typical of the 2 7 2 5 ga and 1 9 1 7 ga periods when voluminous widespread granitoids and large turbidite dominated low p metamorphic belts were produced in settings that are not obviously subduction related therefore a similar process of rift drift delamination riddel tectonics may have periodically operated throughout earth history

hagen brae a surging glacier in north greenland 35 years of observations we use remotely sensed ice velocities in combination with observations of surface elevation and glacier area change to investigate the dynamics of hagen brae north greenland in high detail over the last 35 years from our data we can establish for the first time that hagen brae is a surge type glacier with characteristics of both alaskan and svalbard type surging glaciers we argue that the observed surge was preconditioned by the glacier geometry and triggered by englacially stored meltwater at present the glacier is in a transitional state between active and quiescence phases and is not building up to its pre surge geometry we suggest that the glacier is adjusting to the loss of its floating section general thinning and changes in fjord conditions that occurred over the study period which are unrelated to the surge behavior the high temporal resolution of the ice velocity data gives insight to the sub annual glacier flow

contribution to the glaciology of northern greenland from satellite radar interferometry interferometric synthetic aperture radar insar data from the ers 1 and ers 2 satellites are used to measure the surface velocity topography and grounding line position of the major outlet glaciers in the northern sector of the greenland ice sheet the mass output of the glaciers at and above the grounding line is determined and compared with the mass input we find that the grounding line output is approximately in balance with the input except for the three largest glaciers for which the mass loss is 4 3 km3 ice year 1 or 11 8 of the mass input along the coast we detect a systematic retreat of the grounding lines between 1992 and 1996 with insar which implies that the outlet glaciers are thinning the inferred coastal thinning is too large to be explained by a few warm summers glacier thinning must be of dynamic origin that is caused by spatial and temporal changes in ice velocity iceberg production from the glaciers is uncharacteristically low it accounts for only 8 of the ice discharge to the ocean about 55 of the ice is lost through basal melting 5 8 m ice year 1 on average from the underside of the floating glacier tongues that are in contact with warm ocean waters mass losses are highest in the first 10 km of floating ice where ice reaches the greatest depths and basal melting is 3 times larger than on average only a small increase in basal melting would suffice to disintegrate the floating glacier tongues copyright 2001 by the american geophysical union

geochronology geochemistry and tectonics of the ne bayuda desert n sudan implications for the western margin of the late proterozoic fold belt of ne africa abstract five suites of rocks collected from the precambrian basement in the ne bayuda desert of central northern sudan give late proterozoic whole rock rb sr isochron ages the abu harik complex thought by some previous workers to be an older basement gives an age of 898 51 ma upper amphibolite facies metasediments give a metamorphic age of 761 22 ma the supposedly younger greenschist facies el koro volcanic series were erupted 800 83 ma ago these are chemically similar to the volcanics which unconformably overlie the sol hamed ophiolite in the red sea hills of ne sudan and to some modern island are volcanics the metasediments were intruded 678 43 ma ago by the diefallab granite which is itself deformed the younger weakly deformed amaki series with a basal conglomerate containing basement clasts overlain by purple grits is probably equivalent to the molasse type hammamat group of the eastern desert of egypt which was deposited between 616 and 596 ma ago finally the post tectonic shallal granite with within plate geochemistry was intruded 549 12 ma ago geochemical data suggest that the abu harik complex the el koro volcanic series and the diefallab granite are arc related magmatic rocks they were intruded into or thrust onto shallow water shelf sediments during subduction and then collision between c 900 and 550 ma the data presented here give no support to previous views that the high grade metasediments were metamorphosed prior to the late proterozoic events that they unconformably overlie a still older perhaps archaean basement or that they are unconformably overlain by younger late proterozoic low grade volcanics the precambrian rocks along the e side of the bayuda desert must now all be assigned to the late proterozoic and the boundary between this late proterozoic fold belt and an older craton known to crop out at jebel uweinat must lie farther to the w

geochemistry and isotopic characteristics of mafic phulad ophiolite and related rocks in the delhi supergroup rajasthan india implications for rifting in the proterozoic abstract regionally metamorphosed mafic rocks phulad ophiolite in the delhi supergroup n w india have tholeiitic compositions the data indicate that there are two independent rock suites phulad barr jetgarh pbj meta basalts with element abundances and ratios resembling midocean ridge basalts morb and ranakpur desuri r d meta basalts and meta gabbros with relatively high al2o3 and low tio2 for similar mgo and high lil element rb ba sr coupled with low hfs zr nb and ree sm nd abundances the compositions of these rocks are characteristic of ocean arc basalts dioritic rocks at ranakpur exhibit low k tholeiitic differentiation trends and have close chemical affinity with the spatially associated meta basalts ranakpur diorites define a sm nd whole rock isochron corresponding to an age of 1012 78 ma with an initial nd isotopic composition that is similar to bulk earth sm nd mineral isochrons for a meta gabbro diorite and quartz diorite at ranakpur correspond to ages of 838 36 835 43 and 791 43 ma respectively these younger ages reflect metamorphic re equilibration of isotope compositions during widespread granite and granodiorite emplacement in this region during the late proterozoic model sm nd ages for the meta basalts calculated relative to undepleted mantle vary between 1300 1700 ma the chemistry of both mafic rock suites indicates derivation from source regions which had been depleted during previous melting episodes so the model ages are a maximum age constraint ranakpur desuri mafic rocks have negative initial nd 1 0 to 4 5 and low sm nd ratios suggesting crustal contamination or reworking with a few exceptions the pbj meta basalts have positive initial nd 1 5 to 4 8 indicating that they were derived from heterogeneously enriched although longterm depleted mantle the chemical data support the hypothesis that the pbj meta basalts are fragments of proterozoic ocean crust

geochronology of the arabian nubian shield in southern israel and eastern sinai the metamorphic and igneous orogenic basement rocks of southeastern israel and eastern sinai evolved as part of the arabian nubian shield during latest proterozoic time pelitic schist of the elat association from wadi nahal shlomo south of eilat israel is dated at about 800 m y but the geologic significance of this date is not clear in southeastern sinai metapelitic rocks of the kid group have a date of diagenesis or metamorphism of about 615 m y syn orogenic and post orogenic plutons which intrude the layered metamorphic complex s are dated at 600 m y near eilat and 590 m y at wadi kid other dated plutons include the timna granite at 592 7 m y in the area of nevi ot at 595 m y and in the vicinity of dahab at 588 2 m y and 595 0 3 m y the radiometric dates and low initial 87 sr 86 sr ratios 0 7034 imply that pre 1000 m y continental sialic crust was not involved in the formation of the shield in southeast israel and eastern sinai

thermally controlled glacier surging bakaninbreen in svalbard and trapridge glacier in yukon territory canada are two prominent examples of surging glaciers which are thought to be controlled by their thermal regime both glaciers have developed large bulges which have propagated forward as travelling wave fronts and which are thought to divide relatively stagnant downstream cold based ice from faster moving warm based upstream ice additionally both glaciers are underlain by a wet metres thick layer of deforming till we develop a simple model for the cyclic surging behaviour of these glaciers which interrelates the motion of the ice and till through a description of the subglacial hydrology we find that oscillations surges can occur if the subglacial hydrological transmissivity is sufficiently low and the till layer is sufficiently thin and we suggest that these oscillations are associated with the development and propagation of a travelling wave front down the glacier we therefore interpret the travelling wave fronts on both trapridge glacier and bakaninbreen as manifestations of surges in addition we find that the violence of the surge in the model is associated with the resistance to ice flow offered by undulations in the bed and the efficiency with which occasional hydrological events can release water accumulated at the glacier sole

paleomagnetism and tectonic evolution of the pan african damara belt southern africa paleomagnetic results are reported from the nosib otavi and mulden groups of the damara supergroup a late precambrian shelf sequence on the southern margin of the congo craton in namibia three magnetizations were isolated in the nosib group samples in order of decreasing blocking temperature they are nq1 n 6 sites 28 n 323 e 95 15 nq2 n 7 sites 51 s 213 e 95 12 and nq3 n 13 samples 09 n 295 e 95 13 overall precision of all three magnetizations upon tectonic correction suggests that they predate pan african 650 450 ma folding two magnetizations were isolated in the otavi group samples above the nosib in stratigraphic sequence the dc1 component of possible prefolding age n 4 sites 52 s 186 e 95 35 has been over printed by the dc2 magnetization n 10 sites 55 s 044 e 95 15 of probable postfolding age a single magnetization of probable pre folding age was isolated in the overlying mulden group samples n 6 sites 12 s 090 e 95 16 together with previously published paleomagnetic data from africa the new data showed that no great relative movements have occurred between the congo and kalahari cratons during the interval of pan african tectonism in the damara belt mcelhinny and mcwilliams 1977 continental collision preceded by large relative displacements and closure of a wide ocean e g a himalayan analog is effectively ruled out for the damara belt we develop an alternative model consistent with the available paleomagnetic and geologic data which invokes rifting heating and stretching of the lithosphere underneath the damara belt followed by delamination of the subcrustal lithosphere hot asthenospheric material rises to take the place of the detached and sinking lithospheric base inducing subduction and interstacking of continental crust the much thickened continental crust is partially melted at depth intruded by synorogenic and postorogenic granites and finally uplifted and eroded to its present level of exposure the model is compatible with plate tectonics in that the development of the damara belt can be broadly compared with modern marginal seas with the exception that stretching of the lithosphere was not induced by secondary convection above a downgoing slab possible causes for stretching are rising mantle plumes or intracontinental distortion within the pre damara african plate

a sensitivity study of annual area change for greenland ice sheet marine terminating outlet glaciers 1999 2013 the mass flux from marine terminating glacier outlets from the greenland ice sheet is a significant mass budget term yet glacier calving sensitivity to climate parameters is not well understood in this study the front area changes of 42 marine terminating greenland outlet glaciers were measured annually from 1999 to 2013 using optical satellite imagery thirty five glaciers retreated while seven remained stable the average front position change was 240 m a 1 and the total rate of front area change was 114 km 2 a 1 the yearly average area changes of all measured glaciers are compared with interannual variations in sea surface temperature sst sea ice concentration sic surface melt northern hemisphere nh surface air temperatures and the north atlantic oscillation nao index we find 1 northwestern glaciers area change have a significant correlation with surface melt and nh land temperature variations 2 southeastern glaciers have a significant correlation with local sst sic and nh temperatures and 3 southwestern glaciers area change correlate significantly with local sst and nao index we conclude that a climate sensitivity signal emerges considering a population of glaciers further we find a significant correlation between the date of minimum extent and glacier latitude area change data are available from http gac geus dk

island arcs and their role in the evolution of the western arabian shield abstract two northeast trending late precambrian ensimatic island arc systems in western saudi arabia are described each displays lithotec tonic provinces that conform to those found in modern examples of plate convergence the younger hijaz arc system 800 700 ma contains a thick fore arc sequence of al ays group turbidites overlying an accretionary prism of metamorphosed and fragmented volcanosedimentary rocks and associated ophiolites of the farri group and the al hinu formation the older asir arc system 900 700 ma is exposed at a much deeper erosional level in which only remnant arc and fore arc deposits are present it is identi fied in part by a frontal arc assemblage of abundant dioritic intrusions and high grade metamorphic rocks that are interpreted as a high t low p belt a mafic volcanic assem blage in th back are c area appears to deline ate an interarc basin situated between the at ta if frontal arc and a lithologically similar remnant arc west of bishah about 700 ma ago the hijaz island arc collided with the asir arc system along a southeast dipping subduction zone now rec ognized as the bi r umq port sudan suture epeirogeny during this period led to the crea tion of an intramassif basin in the hijaz arc system and an accretionary basin in the asir arc system these were filled by volcanic and shallow water to continental molasse depos its of the hadiyah and fatimah groups re spectively continued convergence between 700 and 675 ma ago resulted in development of the northeast trending samran fold belt the collision event marks the cessation of an episode of southeast convergence that is in terpreted as the initial phase in the progres sive eastward evolution of the arabian nubian shield introduction

genesis of granitoid batholiths of peninsular malaysia and implications for models of crustal evolution evidence from a ndsr isotopic and upb zircon study nd sr and u pb isotopic data for the late triassic west coast province batholiths and permian to triassic east coast province batholiths of peninsular malaysia allow estimates of the ages of the crustal fragments comprising the peninsula to be made initial nd and sr values for granitoids from the west coast province range from 6 to 10 and 160 0 716 to 660 0 751 respectively nd model ages calculated based on a depleted mantle evolution model tdmnd range from 1300 ma to 1800 ma and are in general agreement with the mid proterozoic upper intersection ages of u pb zircon reverse discordia 1500 1700 ma initial nd and sr values for granitoids from the east coast province range from 0 8 to 6 and 10 0 705 to 130 0 714 respectively calculated tdmnd ages of 900 1400 ma for these granitoids are comparable to two u pb zircon reverse discordia intercepts that yield 800 ma and 1350 ma the general agreement of u pb zircon inheritance ages and tdmnd ages are interpreted to correspond to the proterozoic crust formation ages of the continental fragments represented by the west coast and east coast batholithic provinces mid proterozoic 1300 1900 ma crust formation ages are commonly shown by other phanerozoic continental margin plutonic and volcanic belts the ubiquitous mid proterozoic crust formation ages and the absence of archaean signatures suggest voluminous juvenile additions to the continental crust in the mid proterozoic such ages at continental margins would imply that many continental blocks had achieved very much their present day extent by the mid proterozoic

is there a single surge mechanism contrasts in dynamics between glacier surges in svalbard and other regions 1 during the 1990s monacobreen a 40 km long tidewater glacier in svalbard underwent a major surge we mapped the surge dynamics using ers synthetic aperture radar images differential dual azimuth interferometry and intensity correlation tracking a series of 11 three dimensional 3 d velocity maps covering the period 1991 1997 show a months long initiation and years long termination to the surge with no indication of a surge front travelling downglacier during the surge the front of the glacier advanced 2 km the velocity and derived strain rate increased by more than an order of magnitude and maximum ice flow rates measured during 1994 were 5 m d 1 the spatial pattern of both velocity and strain rate was remarkably consistent and must therefore be controlled by spatially fixed processes operating at the glacier bed we combine these results with those published in the literature to construct a typical svalbard glacier surge cycle and compare this to surge dynamics of glaciers from other cluster regions especially those of variegated glacier in alaska the strong contrast in dynamics suggests that there exist at least two distinct surge mechanisms

how do glaciers surge a review the quasi periodic oscillations between normal and fast motion exhibited by surge type glaciers provide the best observational opportunity to determine limiting conditions that allow fast motion the measurements from variegated glacier prove that its surge motion is caused by rapid sliding induced by high water pressure this arises from a major restructuring of the basal hydraulic system which impedes water discharge prior to and during surge although the evolving glacier geometry and stress distribution play a principal enabling role the seasonal timing of two distinct surge pulses each initiated in winter and terminated in summer indicates a major influence from variable external water inputs this influence is not considered in existing surge models and should promote caution in the use of data from temperate and subpolar surge type glaciers to deduce surge potential in polar ice masses the spatial spreading of surge motion from a zone of local initiation occurs by stress redistribution which may spread the surging zone rapidly upglacier or downglacier inside a region of active ice and by mass redistribution with compressional thickening at the surge front which enables down glacier propagation into less active ice the data from other surge type glaciers including the extensive data from medvezhiy glacier are not inconsistent with the above processes but are inadequate to establish whether completely different mechanisms operate in some surges the way by which water accumulates and produces fast sliding is not established in detail for any surge type glacier and may be different on different glaciers depending for example on the presence or absence of unconsolidated debris between the ice and rock

u pb zircon geochronology and geological evolution of the halaban al amar region of the eastern arabian shield kingdom of saudi arabia u pb zircon model ages for eleven major units from the halaban al amar region of the eastern arabian shield indicate three stages of evolution 1 plate convergence 2 plate collision and 3 post orogenic intracratonic activity convergence occurred between the western afif and eastern ar rayn plates that were separated by oceanic crust remnants of oceanic crust now comprise the ophiolitic complexes of the urd group the oldest plutonic unit in the study is from one of these complexes and gave an age of 694 8 ma detrital zircons from the sedimentary abt formation of the urd group which is intercalated with the ophiolitic rocks were derived from source rocks with a mean age of 710 ma the abt formation may be an accretionary wedge on the western margin of the ar rayn plate plate convergence was terminated by collision of the afif and ar rayn plates during the al amar orogeny which began about 670 ma during collision the urd group rocks were deformed and in part obducted on to one or both plates synorogenic leucogranitoid rocks were intruded from 670 to 640 ma from about 640 to 630 ma widespread unfoliated dioritic plutons were emplaced in the ar rayn block and represent the end of orogenesis related to collision there is no definitive evidence for a significantly older basement beneath the study region

short term velocity variations and sliding sensitivity of a slowly surging glacier we use daily surface velocities measured over several weeks in 2007 and 2008 on a slowly surging glacier in yukon canada to examine the ordinary melt season dynamics in the context of the ongoing surge horizontal velocities within and just below the 1 5 km long zone of fastest flow where the surge is occurring are often correlated during intervals of low melt this correlation breaks down during melt events with the lower reaches of the fast flow zone responding first velocity variability in this lower reach is most highly correlated with melt velocities above and below appear to respond at least as strongly to the velocity variations of this reach as to local melt gps height records are suggestive of ice bed separation occurring in the fast flow zone but not below it pointing to a hydrological cause for the short term flow variability in the surging region independent velocity measurements over 6 years show a maximum july flow anomaly coincident with the location most responsive to melt results from a simple model of dashpots and frictional elements lend support to the hypothesis that this zone partly drives the dynamics of the ice above and below it we speculate that the slow surge may enhance glacier sensitivity to melt season processes including short term summer sliding events

typhoon induced upper ocean cooling off northeastern taiwan 1 the ocean cooling off northeastern taiwan induced by typhoons is complicated by the presence of the continental shelf of the east china sea and the kuroshio the cooling is primarily due to the upwelling of the kuroshio s subsurface water which accompanies the kuroshio s intrusion onto the shelf rather than the entrainment mixing generated by the wind the kuroshio s intrusion in this region has a seasonal variation being more substantial in winter than in summer previous studies found that the winter northeasterly monsoon creates an intrusion favored flow pattern while the reversed summer monsoon opposes it this study found that the strong northeast wind accompanied by a typhoon along a certain path could significantly alter the circulations on the shelf an intrusion event will be triggered via a similar mechanism as induced by the winter monsoon but at a faster pace a numerical study and observation data are provided to illustrate this mechanism

does englacial water storage drive temperate glacier surges hydrological studies of surge type and steady flow glaciers combined with recent space borne synthetic aperture radar interferometry measurements of the motion of bagley ice valley alaska u s a during its 1993 95 surge suggest a temperate glacier surge hypothesis that is consistent with observational evidence and appears capable of shedding light on several aspects of surge behavior we propose that the fundamental driver of temperate glacier surges is englacial storage of water combined with gravity driven movement of stored water to the bed during winter whether a given glacier is surge type is a matter not of whether but of the degree to which these processes occur a surge type glacier must have sufficient storage capacity for continued downward movement of englacially stored water during winter to finally overwhelm the constricted basal drainage system thereby forcing pervasive failure of the subglacial till or alternatively widespread and rapid basal sliding thus initiating a surge we further propose that the sufficient storage capacity requirement is most easily met by glaciers with large thickness which are therefore likely to be long and to have on average low surface slopes the average length of the surge cycle in a given region appears to be a function of the mass balances which after each surge determine the time required to restore glaciers to their pre surge geometries we suggest that the stochastic timing of surge onset for a particular glacier however is a result of the uncertainty of the meteorological conditions required to cause englacial storage of a sufficiently large volume of water

multisatellite observation on upwelling after the passage of typhoon hai tang in the southern east china sea 1 the serial remote sensing based imageries clearly revealed large scale of upwelling within large regional enhancement of chlorophyll a chl a concentration in the southern east china sea ecs after the passage of super typhoon hai tang in july 2005 after the typhoon on 22 july the upwelling area 3 0 mg m3 appeared in the shelf region where the high chl a pattern matched the upwelling in terms of location and time on the other hand a large offshore sst cooling was also observed mainly to the right of typhoon track on 20 july it lasted in a period of 2 3 days this paper provides clear and high resolution evidence that typhoon significant increased upwelling and chl a concentration in the southern ecs

thermal modelling in low pressure high temperature metamorphic belts abstract low pressure high temperature metamorphic belts occur throughout the world they display a characteristic metamorphic style which has remained unchanged with time they are found in disparate tectonic settings including magmatic arcs regions of extension regions of thickened crust in continent continent collision zones and accretionary wedges they are commonly characterized by an abundance of granitoid plutons pressures of metamorphism are primarily less than or equal to that of the aluminosilicate triple point approximately 4 kbar while temperatures are in the range 500 750 c with rare exceptions inferred ptt paths are nearly isobaric and recrystallization was rapid and prograde metamorphic thermal gradients are commonly in the range 60 150 c km these conditions necessitate the presence of a large component of advective heat transfer and or anomalously high basal heat flow during metamorphism the large magmatic fluxes associated with the formation of magmatic arcs provide an adequate heat source for low pressure metamorphism lpm lithospheric extension is likely to produce lpm only if the degree of thinning is large 3 and there is additional heat from magmas the generation of lpm by crustal thickening requires either a large component of advective heating by magmas anomalously high basal heat flow or pre thickening lithospheric extension lpm in this environment must necessarily be accompanied by plutonic activity advection of heat by aqueous fluids may provide a significant contribution to the thermal budget but acting along is unlikely to produce lpm regional lpm induced by advective sources rarely occurs along a geotherm which increases monotonically with depth or synchronously across the region at a given depth it occurs over time as a series of overlapping temporally separate and spatially localized thermal events

how much do we really know about glacier surging some of the ideas about glacier surging are considered mainly but not entirely in the light of observations of temperate glaciers in alaska u s a made within the last 15 years climate has an influence on surge recurrence interval climate and weather also affect surge initiation termination and magnitude regional studies lead to the speculation that subglacial till plays a key role in surging and it has been found under all surge type glaciers studied so far including black rapids and variegated glaciers alaska in most of the glaciers studied till deformation processes dominate the motion in quiescence the linked cavity model of surge triggering and rapid motion is not consistent with these observations but the limited coverage of the observations does not rule it out under parts of the glaciers studied the till observations in alaska raise old questions about the interaction between till and the hydraulic systems of temperate glaciers the role of stored water which observations show to be active even in winter on black rapids glacier is noted

dynamics of tidewater surge type glaciers in northwest svalbard the evolution of ice dynamics through surges of four tidewater terminating glaciers in northwest svalbard is investigated by remote sensing a 20 year time series of glacier surface flow speeds and frontal positions is presented covering the recent surges of monacobreen comfortlessbreen blomstrandbreen and fjortende julibreen surface flow speeds were derived using feature tracking between pairs of ers sar and alos palsar images while frontal positions were taken from the same imagery as well as more frequent but lower spatial resolution envisat wide swath mode images during all four surges increased ice flow caused the tidewater margin to advance while the calving flux was initially reduced to near zero due to compressive stresses limiting crevasse propagation as ice speed decreased the terminus continued to advance until the glacier s speed had returned to its pre surge flow rate only at this time did the terminus start to retreat and peak iceberg calving flux was established we conclude that terminus advance closely tracks glacier speed up that there is little mass loss through calving during the most active phase of the surge and that seasonal cycles of terminus positions diminish during the active surge phase

old model nd ages in namibian pan african rocks the nd isotope analytical technique is a powerful tool for studying many geological processes particularly the evolution of the upper mantle as seen through the isotope and trace element geochemistry of mantle derived volcanic rocks1 3 and magmatic processes along destructive plate margins4 5 however previous studies of continental crust6 8 have been largely restricted to archaean examples and concerned primarily with dating their time of derivation from the upper mantle in the present study we investigated the nd and sr isotope characteristics of rocks involved in a relatively young 800 450 myr orogenic event such events represent critical stages in the evolution of most of the earth s continental crust new material is added from the mantle and pre existing crust is remobilized by erosion and sedimentation deformation and magmatic activity nd and sr isotopes were used to outline the range in age and geochemical characteristics of rock sequences and provinces within both the upper mantle and the pre existing crust which were sampled during the orogeny and hence provided the major components of what is now a stable segment of continental crust

glacier motion estimation using sar offset tracking procedures two image to image patch offset techniques for estimating feature motion between satellite synthetic aperture radar sar images are discussed intensity tracking based on patch intensity cross correlation optimization and coherence tracking based on patch coherence optimization are used to estimate the movement of glacier surfaces between two sar images in both slant range and azimuth direction the accuracy and application range of the two methods are examined in the case of the surge of monacobreen in northern svalbard between 1992 and 1996 offset tracking procedures of sar images are an alternative to differential sar interferometry for the estimation of glacier motion when differential sar interferometry is limited by loss of coherence i e in the case of rapid and incoherent flow and of large acquisition time intervals between the two sar images in addition an offset tracking procedure in the azimuth direction may be combined with differential sar interferometry in the slant range direction in order to retrieve a two dimensional displacement map when sar data of only one orbit configuration are available

forty six years of greenland ice sheet mass balance from 1972 to 2018 we reconstruct the mass balance of the greenland ice sheet using a comprehensive survey of thickness surface elevation velocity and surface mass balance smb of 260 glaciers from 1972 to 2018 we calculate mass discharge d into the ocean directly for 107 glaciers 85 of d and indirectly for 110 glaciers 15 using velocity scaled reference fluxes the decadal mass balance switched from a mass gain of 47 21 gt y in 1972 1980 to a loss of 51 17 gt y in 1980 1990 the mass loss increased from 41 17 gt y in 1990 2000 to 187 17 gt y in 2000 2010 to 286 20 gt y in 2010 2018 or sixfold since the 1980s or 80 6 gt y per decade on average the acceleration in mass loss switched from positive in 2000 2010 to negative in 2010 2018 due to a series of cold summers which illustrates the difficulty of extrapolating short records into longer term trends cumulated since 1972 the largest contributions to global sea level rise are from northwest 4 4 0 2 mm southeast 3 0 0 3 mm and central west 2 0 0 2 mm greenland with a total 13 7 1 1 mm for the ice sheet the mass loss is controlled at 66 8 by glacier dynamics 9 1 mm and 34 8 by smb 4 6 mm even in years of high smb enhanced glacier discharge has remained sufficiently high above equilibrium to maintain an annual mass loss every year since 1998

a general theory of glacier surges we present the first general theory of glacier surging that includes both temperate and polythermal glacier surges based on coupled mass and enthalpy budgets enthalpy in the form of thermal energy and water is gained at the glacier bed from geothermal heating plus frictional heating expenditure of potential energy as a consequence of ice flow enthalpy losses occur by conduction and loss of meltwater from the system because enthalpy directly impacts flow speeds mass and enthalpy budgets must simultaneously balance if a glacier is to maintain a steady flow if not glaciers undergo out of phase mass and enthalpy cycles manifest as quiescent and surge phases we illustrate the theory using a lumped element model which parameterizes key thermodynamic and hydrological processes including surface to bed drainage and distributed and channelized drainage systems model output exhibits many of the observed characteristics of polythermal and temperate glacier surges including the association of surging behaviour with particular combinations of climate precipitation temperature geometry length slope and bed properties hydraulic conductivity enthalpy balance theory explains a broad spectrum of observed surging behaviour in a single framework and offers an answer to the wider question of why the majority of glaciers do not surge

pathways of meltwater export from petermann glacier greenland abstractintrusions of atlantic water cause basal melting of greenland s marine terminating glaciers and ice shelves such as that of petermann glacier in northwest greenland the fate of the resulting glacial meltwater is largely unknown it is investigated here using hydrographic observations collected during a research cruise in petermann fjord and adjacent nares strait onboard icebreaker i b oden in august 2015 a three end member mixing method provides the concentration of petermann ice shelf meltwater meltwater from petermann is found in all of the casts in adjacent nares strait with the highest concentration along the greenland coast in the direction of kelvin wave phase propagation the meltwater from petermann mostly flows out on the northeast side of the fjord as a baroclinic boundary current with the depth of maximum meltwater concentrations approximately 150 m and shoaling along its pathway at the outer sill which separates the fjord from the ambient ocean approximately 0 3 msv 1 sv

slow surge of trapridge glacier yukon territory canada 1 trapridge glacier a polythermal surge type glacier located in the st elias mountains yukon territory canada passed through a complete surge cycle between 1951 and 2005 air photos 1951 1981 and ground based optical surveys 1969 2005 are used to quantify the modifications in flow and geometry that occurred over this period yearly averaged flow records suggest that the active phase began 1980 and lasted until 2000 the average velocity in the central area of the glacier went from 16 m yr 1 in 1974 to 39 m yr 1 in 1980 it peaked at 42 m yr 1 in 1984 and remained above 25 m yr 1 until 2001 over that interval the flow decelerated by steps in 4 year pulses after a particularly vigorous acceleration in 1997 1999 the glacier gradually slowed to presurge velocities in 2005 the flow was less than 9 m yr 1 digital elevation models are generated by stereographic analysis of air photos for 1951 1970 1972 1977 and 1981 these models are updated annually using ground based survey data and a novel implementation of bayesian kriging over the course of the surge the front of active ice advanced 450 m and the glacier area increased by 10 with an associated thinning of the ice the previous surge of trapridge glacier starting before 1939 and ending before 1951 led to a terminus advance of 1 km comparison of the two surges suggests that the 1930s surge started with a slow progression similar to what we observed in the 1980s and 1990s and switched to a faster flow mode after 1941 this second phase was never attained in the recent surge probably owing to a lack of mass

spreading of warm ocean waters around greenland as a possible cause for glacier acceleration we examine the pattern of spreading of warm subtropical origin waters around greenland for the years 1992 2009 using a high resolution 4km horizontal grid coupled ocean and sea ice simulation the simulation provided by the estimating the circulation and climate of the ocean phase ii ecco2 project qualitatively reproduces the observed warming of subsurface waters in the subpolar gyre associated with changes of the north atlantic atmospheric state that occurred in the mid 1990s the modeled subsurface ocean temperature warmed by 1 5 c in southeast and southwest greenland during 1994 2005 and subsequently cooled by 0 5 c modeled subsurface ocean temperature increased by 2 2 5 c in central and then northwest greenland during 1997 2005 and stabilized thereafter while it increased after 2005 by xu and others 2012 we show that the oceanic changes have very likely increased the subaqueous melt rates of the glacier fronts and in turn impacted the rates of glacier flow

late proterozoic transpression on the nabitah fault system implications for the assembly of the arabian shield abstract the longest proposed suture zone in saudi arabia the nabitah suture can be traced as a string of ophiolite complexes for 1200 km along the north south axis of the arabian shield results of a field study in the north central shield between 23 and 26 n indicate that the nabitah suture is indeed a major crustal discontinuity across which hundreds of kilometers of displacement may have occurred on north south trending subvertical faults of the nabitah fault system although not a unique solution many structures within and near these faults can be reconciled with transpression i e convergent strike slip and syntectonic emplacement of calc alkaline plutonic rocks transcurrent motion on the nabitah fault system appears to have began prior to 710 ma was active circa 680 ma and terminated prior to significant left lateral strike slip on the najd fault system which began sometime after 650 ma northwest directed subduction in the eastern shield could have produced the observed association of calc alkaline magmatism and left lateral transpressive strike slip and is consistent with interpretation of the abt schist and sedimentary rocks of the murdama group as relics of the associated accretionary wedge and fore arc basin

sermeq model produces a realistic upper bound on calving retreat for 155 greenland outlet glaciers the rate of land ice loss due to iceberg calving is a key source of variability among model projections of 21st century sea level rise it is especially challenging to account for mass loss due to

geochemical and sr nd pb isotopic data bearing on the origin of pan africangranitoids in the kid area southeast sinai egypt the kid plutonic suite in southeast sinai egypt is composed of 1 a gabbro diorite complex 2 quartz monzodiorite 3 granodiorite monzogranite association 4 syenogranite major and traceelement analyses and radiogenic isotope data rb sr sm nd and pb pb are presented for these rocks rb sr isochrons indicate ages of 581 11 ma 576 11 ma and 570 4 ma for the quartz monzodiorite granodiorite monzogranite association and syenogranite respectively the gabbro diorite complex is a layered intrusion varying in sio2 from 42 to 59 wt it shows a calc alkaline trend and the trace element characteristics of arc lavas subsequently this magma fractionated to give quartz monzodiorite andsyenogranite magmas the quartz monzodiorite has low initial 87 sr 86 sr ratios 0 703 and high nd values 4 4 0 3 with trace element characteristics of volcanic arc granites the granodiorite monzograniteassociation has higher initial sr ratio 0 7044 lower nd 1 5 2 7 and relatively high 207 pb 204 pb and 208 pb 204 pb significantly different from those of the older rocks isotopic data and ree modelling suggestthat it formed by partial melting of an early pan african amphibolitic lower crust the syenogranite isa typical highly fractionated post orogenic granite with a deep negative eu anomaly hfse and reeenrichment a 87 sr 86 sr initial ratio of 0 7033 nd of 4 5 0 5 and distinct variations in the 206 pb 204 pbratio the isotopic compositions of sr nd and pb indicate that the syenogranite and the quartzmonzodiorite are comagmatic increasing fluorine concentration from the quartz monzodiorite to thesyenogranite suggests that fluid fractionation involving fluorine complexing played an important role inthe genesis of the syenogranite this process led to the enrichment of hfse and hree to extensivefractional crystallization to changes in the u pb ratios and a distinct variation in 206 pb 204 pb

the arabian infracambrian extensional system abstract during the late precambrian and early cambrian about 600 540 ma extensive left lateral faulting along the complex nw se trending najd fault system cut across the arabian shield this tectonic episode was accompanied by nw se directed extension in northern egypt and the sinai peninsula based on these relationships stern 1985 interpreted the najd fault system as a set of transform faults emanating from a rift basin in ne egypt contemporaneous to this system in the western part of the arabian plate and northern egypt extensive evaporitic basins developed in northern pakistan southern oman and the arabian gulf and zagros mountains these basins are generally bounded by nw trending faults such as the najd hawasina and zagros faults and ne trending faults such as the ghudun khasfah and dibba faults these evaporitic basins are interpreted as rift basins such that stern s 1985 extensional model in northern egypt may be expanded regionally to include the eastern part of the arabian plate and the indian subcontinent this broader interpretation implies that after the e w directed collisional tectonics of the late precambrian in western arabia and africa which terminated around 640 600 ma the arabian plate experienced nw se directed crustal extension and continental break up

glacier surge mechanism 1982 1983 surge of variegated glacier alaska the hundredfold speedup in glacier motion in a surge of the kind the kind that took place in variegated glacier in 1982 1983 is caused by the buildup of high water pressure in the basal passageway system which is made possible by a fundamental and pervasive change in the geometry and water transport characteristics of this system the behavior of the glacier in surge has many remarkable features which can provide clues to a detailed theory of the surging process the surge mechanism is akin to a proposed mechanism of overthrust faulting

mass balance change as a control on the frequency and occurrence of glacier surges in svalbard norwegian high arctic the end of the little ice age lia in svalbard 76 81 n a climate sensitive region at the northern extreme of strong poleward heat transfer was marked by an abrupt increase in mean annual air temperature of up to 5 c around 1920 glacier mass balance has been consistently negative since this time and large cumulative net losses of mass have occurred at most glaciers energy balance modelling confirms the sensitivity of svalbard glaciers to climate change predicting a negative shift in net mass balance of up to 0 8 m a 1 water equivalent per degree temperature rise this climate related shift in glacier mass balance has reduced the intensity of glacier surge activity in svalbard one glacier known to have surged since the end of the lia has since failed to accumulate the mass required to re initiate the surge cycle and is also now cold at its base and incapable of rapid flow by basal sliding three overviews of the total number of actively surging glaciers in svalbard between 1936 90 show a decrease from 18 to 5 this is significant compared with the expected numbers of surges based on lia conditions post lia climate change in svalbard has therefore affected not only glacier extent but also ice dynamics this is trend will probably continue given co2 induced climate warming

a new geobarometer for the assemblage biotite muscovite chlorite quartz the equilibrium thermodynamics of the reaction 4kmga1si40 o oh mg5a1 si30 o oh muscovlte chlorite muscovite biotite ka13si 0 oh 3kmg3aisi 0 0 oh 7si0 4h o quartz fluid can be formulated as a geobarometer thermo dynamic data for the mg a1 celadonite end member of muscovite is derived from the reversed mineral equilibria experiments of velde i 965 using the calculation method of powell 1978 giving afh 1298 5823 5 kj s 1298 0 3060kjk v 1298 13 8kjkbar

satellite views of the episodic terrestrial material transport to the southern okinawa trough driven by typhoon using satellite derived water transparency alias secchi depth images we found clear signals of terrestrial material transport to the southern okinawa trough triggered by the typhoon morakot in august 2009 three sources were identified one is from the eastern coast of taiwan another is from the western coast of taiwan and the other is from the coast of mainland china carried by northward flows typhoon triggered terrestrial materials from both sides of taiwan s coasts were transported to the region northeast of taiwan moreover the terrestrial material from the coast of mainland china could cross the taiwan strait and be further transported to the region northeast of taiwan these typhoon induced terrestrial materials off northeastern taiwan could then be transported to the southern okinawa trough along the western edge of the kuroshio in addition to the particulate terrestrial material transported nutrients might also be transported to the kuroshio main stream a significant phytoplankton bloom was observed along the kuroshio path for about 300 km off northeast of taiwan our results indicate that episodic cyclone driven terrestrial material transport could be another source of mud in the southern okinawa trough

transient modulation of kuroshio upper layer flow by directly impinging typhoon morakot in east of taiwan in 2009 this study deals with the modulation of the kuroshio upper layer flow kulf in response to the passage of typhoon morakot in 2009 using regional oceanic modeling system roms and in situ measurements from argos drifters and argo floats the analysis of the simulated current fields near the typhoon track revealed an intermittency phenomenon of the kulf which was almost shut down for at least 6 hours the process begun 2 days prior to the approach of typhoon center due to blockage of the kulf by the steadily northerly winds and lasted for more than 2 days simultaneously shifting the kuroshio main stream kms path when the morakot gradually moved closely to the kuroshio the kms shifted vertically from the surface layer to deeper layer of 50 100 m depth and the maximum current speed in the kms decreased from more than 1 3 m s 1 to less than 1 1 m s 1 when the morakot center approached about 100 km to the original position of the kuroshio the kulf spread eastward for 1 5 degrees at 24 n when the morakot center moved to the original position of the kms the kuroshio abruptly rushed with a maximum speed near 1 4 m s 1 meanwhile an offshore cool jet originating from southeastern tip of taiwan was generated and extended northward along the kuroshio in the cool jet the lowest temperature reached about 5 c lower than the ambient waters modeled current variations and the cool jet during the morakot passage were validated by in situ measurements

late pan african tectonics marking the transition from subduction related calc alkaline magmatism to within plate alkaline granitoids adrar des iforas mali boullier a m liegeois j p black r fabre j sauvage m and bertrand j m 1986 late pan african tectonics marking the transition from subduction related talc alkaline magmatism to within plate alkaline granitoids adrar des iforas mali in b johnson and a w bally editors intraplate deformation characteristics processes and causes tectonophysics 132 233 246 the pan african trans saharan belt resulting from oceanic closure and oblique collision between the west african craton and the tuareg nigerian shields around 600 ma ago displays in the iforas a rapid switch from subduction and collision related talc alkaline magmatism to typical a type granitoids 560 540 ma the transition is clearly seen in associated spectacular acid dyke swarms early talc alkaline e w trending sets being cut by alkaline n s trending arrays isotopic evidence shows that the change in chemistry involves a different more primitive mantle source structural observations indicate that the transition from talc alkaline to alkaline magmatism is related to reversals in the stress field during and after collision in the model proposed the first major reversal from d with ei ca 13s0n lloon to ds with ui ca 50 n 60 n is thought to have been responsible for the slicing of the subducted plate thereby allowing the rise to shallow depth beneath the continental lithosphere of asthenospheric mantle believed to be the source of the alkaline magmatism the tapping of this new source occurred between ds and d4 events contemporaneous with a rotation of the maximum compressive stress back from 60 n to 105 n

samarium neodymium data on two late proterozoic ophiolites of saudi arabia and implications for crustal and mantle evolution whole rock and mineral samples from the jabal al wask and jabal ess ophiolites northwestern saudi arabia yield sm nd isochron ages of 743 24 ma and 782 38 ma respectively these formation ages which provide maximum limits for possible obduction ages are in broad but not precise agreement with the previously known geologic history of the arabian shield they indicate that the ophiolitic rocks are roughly coeval with nearby volcanic and plutonic rocks supporting a back arc origin for the two ophiolites we suggest that the jabal al wask and jabal ess ophiolites were parts of the same northeast southwest trending ophiolite belt now offset along the najd fault system initial nd values range from 6 6 to 7 6 indicating derivation from a mantle source that has been lil depleted for at least 2 ga reported nd values from the arabian shield that are lower than this suggest the presence of older reworked continental crust

estimation of interannual and interdecadal variations of typhoon induced primary production a case study for the outer shelf of the east china sea 1 using multiplatform satellite data and 13 typhoon passages from 1998 through 2004 an empirical relationship to assess typhoon forced primary production pp enhancement in the outer shelf of the east china sea is introduced the constructed relationship requires variables of typhoon maximum sustained wind typhoon transit speed and bottom depth of the location below the typhoon track as this relationship does not require ocean color data it enabled us to reconstruct the interannual and interdecadal variations of typhoon forced pp enhancement from 2004 back to 1980 typhoon forced pp enhancements and typhoon contributions to summer fall new production during el nino years tended to be higher than those during la nina years typhoon enhanced pp also has shown a tendency to be higher during the 1991 2004 period than during the 1980 1990 one the method we detail in this study is applicable for other tropical cyclone trajectory basins

zabargad and the isotopic evolution of the sub red sea mantle and crust abstract zabargad island in the red sea exposes ultramafic bodies in contact with partially retrograded granulite facies lower crustal rocks the contact could represent the sub red sea moho prior to the opening of the red sea the ultramafic rocks are largely protogranular spinel lherzolites that grade locally to porphyroclastic to mylonitic amphibole peridotites some of the peridotites are infiltrated by high mg gabbros troctolites the peridotites and the lower crustal rocks are cut by diabase dikes the zabargad peridotites are isotopically heterogeneous on a scale of meters or less sr and nd isotopic ratios of clinopyroxenes cpx from spinel lherzolites lie in the depleted portion of the 143 nd 144 nd 87 sr 86 sr mantle array whereas cpx and amphiboles from amphibole peridotites fall off the array towards the low 143 nd 144 nd and sol 87 sr 86 sr field that may characterize portions of the sub continental mantle cpx from troctolites plot in the middle of the 143 nd 144 nd 87 sr 86 sr mantle array and have higher 87 sr 86 sr ratios and more depleted lree patterns than the intruded spinel lherzolites and amphibole peridotites all whole rock lherzolites and peridotites and most diabase dikes from zabargad as well as a variety of rocks from other parts of the red sea area morb glasses a diabase dike from the brothers island basanites and clinopyroxenes from associated nodules from the ataq diatreme in yemen define a linear array on a sm nd isochron diagram with a best fit age of ca 675 ma and an initial nd of 6 7 this array is probably a mixing line between depleted morb type mantle and a low 143 nd 144 nd 87 sr 86 sr metasomatic component the age defined by the linear array may date either an episode of pan african mantle homogenization or in our preferred model the pan african segregation of a previously homogeneous mantle into two or more reservoirs of identical 143 nd 144 nd but different sm nd ratios the subsequent partial remixing of these isotopic reservoirs during metasomatism associated with the opening of the red sea did not perturbed the slope of the array the lree enriched reservoir may have been the pan african lower crust since there is field and textural evidence that the metasomatic fluids were derived from or equilibrated with the adjacent crustal complex alternatively the lree enriched component may have been a mantle reservoir similar to that which generated basalts and nodules from the nearby ataq diatreme the troctolites are isotopically distinct from the host peridotites and retain igneous textures suggesting they intruded the peridotites during the opening of the red sea their isotopic patterns are similar to those of recent volcanics from afar portions of the ataq diatreme and some zabargad dikes indicating derivation from a similar mantle source their very lree depleted patterns suggest they are either re melted fractions of previously very depleted spinel lherzolites or early formed mineral aggregates that became enmeshed in the peridotites as fractionating melt ascended to higher levels our results indicate that at least two major processes metasomatism and intrusion have modified the isotopic pat terns of the spinel lherzolites of zabargad had the resultant chemically and isotopically heterogeneous bodies stayed in the mantle instead of being uplifted to their present positions they would have proven to be enigmatic sources for future basalts and xenoliths