propagation of the great salinity anomaly of the 1990s around the northern north atlantic 1 time series of t and s extending through 2001 are used to describe propagation of the great salinity anomaly of the 1990s gsa 90s comparison of the distance time relations for the gsa 70s 80s and 90s reveals a substantial intensification of the large scale circulation in the northern north atlantic especially in the subarctic gyre between newfoundland and the faroes the advection rate of the gsa 70s 80s and 90s between newfoundland and the faroe shetland channel is conservatively estimated to have been 3 5 10 and 10 cm s respectively the circulation intensification apparently occurred within a decade between the gsa 70s and 80s during the next decade the advection rate increased from 10 to 13 cm s between newfoundland and iceland basin the gsa 90s was advected towards the faroe shetland channel by the northern iceland basin s branch of the north atlantic current whereas the contribution of the southern branch via the rockall trough was minimal

alteration mineralogy and stable isotope geochemistry of paleoproterozoic basement hosted unconformity type uranium deposits in the athabasca basin canada unconformity type uranium deposits are characterized by mineralization developed along the contact between younger sandstone cover and underlying crystalline basement rocks mineralization may extend up to 400 m into the underlying basement rocks whereas sandstone hosted unconformity type deposits have been well studied deposits hosted primarily in the basement have not this study examines the deposits at rabbit lake dawn lake and mcarthur river in the athabasca basin of canada which are hosted by the metamorphic archean and early paleoproterozoic rocks forming the basement to younger late paleoproterozoic sandstones alteration is similar in the three deposits and is characterized by three distinct paragenetic stages 1 preore alteration involving illitization of plagioclase and amphibole followed by chloritization of biotite and illite which formed at ca 230 c 2 ore stage alteration characterized by uraninite and coarse grained illite which formed at ca 240 c 3 postore alteration comprising spherulitic dravite vein chlorite quartz calcite and fe cu co and pb sulfides which formed at ca 135 c fluid circulation associated with emplacement of later mackenzie dikes initiated partial recrystallization of uraninite a later stage of alteration includes kaolinite and iron hydroxide precipitation formed at much lower temperatures of ca 50 c stable isotope compositions of the alteration minerals in conjunction with their paragenesis indicate that oxidized basinal fluids d 43 to 21 18o 3 8 were derived primarily from evolved seawater and leached uranium from the overlying sandstones of the athabasca formation and transported it into the basement via infiltration along fracture zones associated with reverse faults graphitic units in the basement and preore alteration served as both physical fractured zones and chemical reductants traps for the uranium mineralization the basinal fluids were responsible for the preore illite chlorite synore uraninite illite and the early postore alteration events this differs from many other sandstone hosted deposits where both oxidized basinal and reduced basement derived fluids were responsible for uranium precipitation

measurement of u pb ages of uraninite and davidite by laser ablation hr icp ms laser ablation high resolution inductively coupled plasma mass spectrometry la hr icp ms is a rapid accurate and inexpensive technique for making in situ u pb isotopic measurements of uraninite and davidite the advantages of this method include 1 mineral separation and chemical digestion are not required 2 measurements on complex samples are feasible because significant isobaric interferences can be resolved and 3 accurate u pb and 207pb 206pb dates on 10 25 m spots can be obtained rapidly the la hr icp ms method is applied to u oxide minerals from four deposits and prospects from northern australia and the new dates are compared to previously published conventional thermal ionization mass spectroscopy tims dates and to known ages of geologically important events these comparisons permit us to assess elemental fractionation of u and pb for uraninite and davidite of the new method relative to zircon as well as its geochronological accuracy and precision u pb apparent ages measured previously agree well with our measurements for el sherena palette and mt isa additionally the upper intercept 207pb 206pb dates for adelaide river 701 190 ma 1 and palette 841 94 ma 1 uraninite measured here are similar to those previously obtained for palette 730 ma nabarlek 920 ma and koongarra 870 ma and the upper intercept date for el sherena uraninite 1573 160 ma is within error of that previously determined for ranger 1550 15 and 1472 40 ma such apparent age agreement for uraninite and similarly for davidite indicates that u and pb fractionations are within error of that for zircon whereas the inherent imprecision of our dates and their associated mswd values greater than 2 5 probably indicate that multiple resetting events affected our samples analytically these results demonstrate that the la hr icp ms technique provides excellent spatial resolution while also removing argide phosphide sulfide and halide interferences that can otherwise lead to erroneous data when using quadrupole icp ms geologically the individual 207pb 206pb and upper intercept u pb dates of uraninite from adelaide river and palette are ca 800 ma possibly reflecting recrystallization of uraninite during the break up of rodinia

geochronology of unconformity related uranium deposits in the athabasca basin saskatchewan canada and their integration in the evolution of the basin the importance of geochronology in the study of mineral deposits in general and of unconformity type uranium deposits in particular resides in the possibility to situate the critical ore related processes in the context of the evolution of the physical and chemical conditions in the studied area the present paper gives the results of laser step heating 40ar 39ar dating of metamorphic host rock minerals pre ore and syn ore alteration clay minerals and laser ablation inductively coupled plasma mass spectrometer la icp ms u pb dating of uraninite from a number of basement and sediment hosted unconformity related deposits in the athabasca basin canada post peak metamorphic cooling during the trans hudson orogen of rocks from the basement occurred at ca 1 750 ma and gives a maximum age for the formation of the overlying athabasca basin pre ore alteration occurred simultaneously in both basement and sandstone hosted mineralizations at ca 1 675 ma as indicated by the 40ar 39ar dating of pre ore alteration illite and chlorite the uranium mineralization age is ca 1 590 ma given by la icp ms u pb dating of uraninite and 40ar 39ar dating of syn ore illite and is the same throughout the basin and in both basement and sandstone hosted deposits the mineralization event older than previously proposed as well as several fluid circulation events that subsequently affected all minerals studied probably correspond to far field continent wide tectonic events such as the metamorphic events in wyoming and the mazatzal orogeny ca 1 6 to 1 5 ga the berthoud orogeny ca 1 4 ga the emplacement of the mckenzie mafic dyke swarms ca 1 27 ga the grenville orogeny ca 1 15 to 1 ga and the assemblage and break up of rodinia ca 1 to 0 85 ga the results of the present work underline the importance of basin evolution between ca 1 75 ga basin formation and ca 1 59 ga ore deposition for understanding the conditions necessary for the formation of unconformity type uranium deposits

regional setting geology and paragenesis of the centennial unconformity related uranium deposit athabasca basin saskatchewan canada the centennial unconformity related uranium deposit represents the first significant uranium mineralization along the snowbird tectonic zone in the south central part of the athabasca basin the deposit is associated with a steeply wnw dipping contact between the virgin schist group and mylonitic granite of uncertain age virgin schist group rocks in the deposit area include phyllites impure quartzite and quartzite medium to coarse grained microcline augen porphyroclasts characterize the granite the quartzite being resistant to weathering forms a paleotopographic high flanked by a paleotalus which formed prior to athabasca group sedimentation diabase petrographically and geochemically similar to the 1 27 ga mackenzie dikes intrudes the mineralized trend along brittle structures in the basement rocks and athabasca group a detailed paragenetic study of the deposit area reveals a protracted history that is related to the episodic reactivation of brittle structures and associated fluid movement along this significant structural corridor retrograde metamorphism converted biotite to chamosite at temperatures between 335 to 350 c weathering caused the breakdown of microcline and the dissolution of quartz prior to erosion and deposition of the athabasca group which started at about 1750 ma compaction and diagenesis resulted in quartz overgrowths and development of a diagenetic clay assemblage of illite and sudoite at temperatures between 150 and 200 c which was broadly synchronous with primary mineralization clinochlore euhedral quartz carbonate and pyrite was developed after the intrusion of the diabase under reducing conditions primarily at temperatures between 270 to 320 c uranium remobilization and alteration of uraninite to coffinite appears to have taken place after the emplacement of the diabase dikes kaolinite and uranophane form last in the paragenetic sequence and probably form at relatively low temperatures

mineralogy and u pb pb pb and sm nd geochronology of the key lake uranium deposit athabasca basin saskatchewan canada the key lake deposit is one of several large high grade unconformity related uranium deposits located at the eastern margin of the athabasca basin in northern saskatchewan canada the deposit consists of the gaertner orebody now mined out and the deilmann orebody which is presently being mined in the past radiometric dating efforts yielded an age of oldest ore forming event of 1250 34 ma at the gaertner orebody and 1350 4 ma at the deilmann orebody this unlikely age difference called for further investigation innovative preparation techniques were used to separate the paragenetically oldest u mineral an anisotropic uraninite ore microscopy and u pb isotopic data show that the oldest event of uranium emplacement occurred simultaneously at the two orebodies at 1421 49 ma the primary ore forming phase was followed by younger generations of u mineralization and periods of remobilization sm nd data of key lake uraninite form an isochron corresponding to an age of 1215 ma this is interpret

the 40ar 39ar dating of magmatic activity in the donbas fold belt and the scythian platform eastern european craton 1 the donbas fold belt is the compressionally deformed southeasternmost part of the intracratonic late paleozoic dniepr donets rift basin it is situated in an intracratonic setting but close to the southern margin of the east european craton south of which lies the scythian platform a range of igneous rocks from the donbas fold belt and the scythian platform were dated by the 40ar 39ar method in order to constrain the ages of magmatic activity in these areas and compare them the plateau ages from the south margin of the donbas fold belt vary from 151 4 4 7 ma to 278 1 5 3 ma and define three main age groups middle late jurassic middle late triassic and early permian the age spectra obtained from the scythian platform samples are often disturbed as a result of limited alteration the proposed ages plateau and pseudoplateau vary from 174 4 2 1 ma to 243 7 1 4 ma and two major age groups are defined in early carboniferous and triassic jurassic times the early permian 285 270 ma and early triassic 245 250 ma ages of magmatic activity are the same in both areas in the late triassic the ages of magmatic activity are slightly different 220 and 205 ma and they are entirely different thereafter these data can be interpreted as indicating a mantle plume as common deep magmatic source

petrogenesis of the proterozoic athabasca basin northern saskatchewan canada and its relation to diagenesis hydrothermal uranium mineralization and paleohydrogeology abstract in the athabasca basin proterozoic sandstones unconformably overlie archean and aphebian rocks multiple fluid events involving isotopically and chemically distinct fluids which have migrated laterally for considerable distances and along fault zones have produced a paragenetically identifiable assemblage of clay silicate and oxide minerals in the basin and basement rocks altered sandstones and the underlying metasedimentary rocks proximal to fault zones host high grade u ni co unconformity type uranium ore deposits and contain an alteration assemblage of highly crystalline 2m 3t illite 1m kaolinite clinochlore and sudoite hematite dravite and euhedral quartz in the sandstones 18o values of coeval quartz hematite quartz illite quartz dravite illite hematite and kaolinite hematite fluid inclusion temperatures in diagenetic quartz and d values of 1m kaolinite 2m 3t illite dravite and in fluid inclusions in the quartz indicate formation from a basinal fluid that had d values of 60 10 and which underwent salinity temperature and 18o increases from 5 to 34 wt nacl 120 to 240 c and 5 to 3 respectively as a result of increasing burial depth and sustained water rock interactions with the basinal sediments over substantial time periods 18 o 16 o and d h ratios of sudoite and clinochlore in meta sedimentary basement rocks within the alteration haloes indicate formation from a basement derived fluid with 18o and d values of 4 4 and 30 10 respectively that was isotopically distinct from the basinal fluids 18o and d values of late kaolinites in reactivated fault zones indicate formation mainly from low temperature 50 25 c fluids having 18o and d values of 16 and 130 respectively similar to relatively modern meteoric waters in the area some kaolinites have 18o and d values which suggest they formed from meteoric waters at mid latitudes and have experienced varying degrees of oxygen and hydrogen isotope exchange with relatively modern meteoric waters in the re activated faults illite sudoite and dravite have d values that vary by 100 without concurrent changes to their 18o values indicating preferential hydrogen isotope exchange with relatively modern meteoric waters at low temperatures and under conditions of high integrated water rock ratios rb sr isochron and model ages of 1477 57 and 952 ma respectively for the crystalline 2m 3t illites indicate the timing of the high temperature basinal fluid events associated with fluid mixing rb sr and k ar ages on illites with the lowest d values are as young as 300 ma and indicate late stage resetting of their radiogenic isotope systematics as a result of substantial interactions with relatively modern meteoric waters the evolution of sr isotopic compositions of fluids in the basin and basement rocks as reflected by the 87 sr 86 sr ratios of chlorite illite and dravite indicates that mixing of two isotopically distinct fluids in the vicinity of faults was the process by which uranium was precipitated similar to that suggested by oxygen and hydrogen isotope systematics in the clays and silicate minerals nd ratios in the high temperature diagenetic and hydrothermal clay and silicate minerals and the cogenetic uranium ores suggest they all have formed from similar fluids which have interacted substantially with the basin sediments in general the isotopic chemical microthermometric and petrologic data indicate that the athabasca basin has had a protracted fluid history comparable to that documented for more modern sedimentary basins the data clearly show that the major sandstone aquifers have been affected by widespread lateral flow of diagenetic fluids over distances of hundreds of kilometers and also that these fluid migration paths have been modified by cross formational fluid flow near active fault zones

numerical simulation of strain localization and its relationship to formation of the sue unconformity related uranium deposits eastern athabasca basin canada abstract unconformity related uranium deposits in the athabasca basin canada are spatially associated with reactivated basement faults that cut the unconformity surface between archean to paleoproterozoic basement and paleoproterozoic to mesoproterozoic sedimentary rocks of the athabasca group the sue deposits sue a b c d and e are located in the eastern athabasca basin along a 2 km long north northeast trending structural corridor and have both sandstone hosted sue a and sue b to the north and basement hosted sue c sue d and sue e to the south orebodies all the deposits are structurally controlled by north northeast trending basement faults that demonstrate different degrees of reverse displacements of the unconformity surface however it is not clear why the mineralization is distributed in such a pattern along the corridor in this study both 2 dimensional 2d and 3 dimensional 3d numerical modeling of deformation were conducted to examine the relationship between the distribution of strain and uranium mineralization the modeling shows that dilation positive volumetric strain thought to correlate with the development of extensional fracture systems and dilational jogs that represent potential mineralization sites is primarily controlled by the rheological contrasts in basement rocks and the degree of deformation the presence of faulted graphitic pelitic gneiss associated with the sandstone hosted sue a and sue b deposits favours dilation localized within the sandstone at low degrees of deformation mainly due to the overlying competent hangingwall granitic gneiss in contrast the basement hosted sue c sue d and sue e deposits are associated with dilation zones localized along the contact between the faulted graphitic pelitic gneiss and competent footwall silicified gneiss at higher degrees of deformation the modeling results highlight the importance of both graphitic basement structures and strong rheological contrasts between basement rocks in uranium exploration in the athabasca basin

low temperature oxygen isotopic fractionation in the uraninite uo3 co2 h2o system oxygen isotope fractionation factors for uraninite water and uo3 water were determined from a series of uraninite co2 and uo3 co2 exchange experiments between 100 and 300 c the measured fractionation factors are similar to the theoretical fractionation factors of hattori and halas 1982 at high temperatures and zheng 1991 at low temperatures and are nonlinear over the temperature range examined regression through these curve gives 1000 ln uo2 h2o 16 58 106 t2 77 52 103 t 77 48 1000 ln uo3 h2o 2 21 106 t2 25 06 103 t 45 90 with 2 errors of 2 5 diffusion coefficients of oxygen with temperature for uraninite and uo3 can be represented by d uraninite 3 1 10 10 exp 63981 rt and d uo3 1 3 10 15 exp 21 197 rt where the activation energies for uraninite and uo3 are 64 0 0 2 kcal mole and 21 2 0 2 kcal mol respectively exceptionally low 18o values of natural uraninites i e 32 to 19 5 from unconformity type uranium deposits in saskatchewan in conjunction with theoretical and experimental uraninite water and uo3 water fractionation factors suggest that primary uranium mineralization is not in oxygen isotopic equilibrium with coeval clay and silicate minerals the low 18o values have been interpreted as having resulted from the low temperature recrystallization of primary uranium mineralization in the presence of relatively modern meteoric fluids having 18o values of ca 18 despite petrographic and u pb isotope data that indicate limited alteration therefore it appears that uranium minerals can exchange oxygen isotopes with later fluids with only limited actinide remobilization and minor disturbances to their original chemical compositions and textures

interdecadal thermocline variability in the north pacific for 1958 97 a gcm simulation an ocean general circulation model is forced with the ncep reanalysis wind stress for 1958 97 to understand mechanisms of ocean subsurface variability with relatively high horizontal 1 83 18 and vertical 41 levels resolutions the model produces mode waters on a range of density surfaces in the western central and eastern north pacific in qualitative agreement with observations these mode waters appear as a thermostad or a region of weak stratification in the upper thermocline as they flow southward from their formation regions in the kuroshio and its extension in the model subsurface temperature variability in the central subtropical gyre reaches a maximum within the thermostad in contrast to what might be expected from the linear baroclinic rossby wave theory this variance maximum is associated with the longitudinal shift in the path of mode waters in particular deepened mixed layer and accelerated eastward currents in the kuroshio extension by wind changes in the mid 1970s act cooperatively to move the central mode waters toward the east causing large subsurface temperature anomalies besides the local maximum in the central north pacific subtropical gyre two additional maxima of the subsurface anomaly are identified in the northwestern and southern parts of the gyre respectively among these subsurface anomaly centers the one in the northwestern north pacific has a strong effect on the model sea surface temperature suggesting that the kuroshio and its extension are a key region to decadal interdecadal ocean atmosphere interaction finally possible effects of atmospheric thermal forcing are discussed

classification seasonality and persistence of low frequency atmospheric circulation patterns abstract orthogonally rotated principle component analysis rpca of northern hemisphere 1 month mean 700 mb heights is used to identify and describe the seasonality and persistence of the major modes of interannual variability the analysis is detailed and comprehensive in that 1 a high resolution approximately equal area 358 point grid is used for the virtually maximum possible 35 year period of record 2 a positive bias in the nmc data base in the early 1950s in the subtropics is largely eliminated for the first time and 3 homogeneous separate analyses of each month of the year are carried out detailing the mouth to month changes in the dominant circulation patterns winter results are similar to those of other recent rpca and teleconnection studies except that some less obvious patterns are identified and further detail of the better known patterns is provided two north south dipole patterns are found over the pacific ocean west pacific oscillation and east pacific pattern and over the atla

u pb geochronology of minerals from the midwest uranium deposit northern saskatchewan analyses of u pb ratios in 30 microsamples of pitchblende and coffinite from the midwest uranium deposit in northern saskatchewan as well as two altered zircons from host rocks indicate an age of

sr isotopic study of helikian sediment and diabase dikes in the athabasca basin northern saskatchewan the athabasca group overlies 1 8 ga or older basement of the churchill province and predates uranium mineralization at 1 3 ga cross cutting diabase dikes have been dated by rb sr mineral isochrons

late quaternary glacial and sedimentary history of bonavista bay northeast newfoundland high resolution seismic profiles and core data from bonavista bay northeast newfoundland show that the sedimentary package above acoustic basement was deposited during the deglaciation of the late wisconsinan ice sheet during the late wisconsinan maximum 20 000 bp bonavista bay was occupied by a grounded ice sheet that extended farther offshore deglaciation of the bay was rapid and occurred prior to 13 500 bp during a time of rising sea level a basal till was deposited beneath the grounded ice and after lift off an ice shelf developed over the outer basins where diamicton was deposited the inner bay gradually deglaciated as the ice margin retreated to the present day shoreline by 13 000 bp and fine grained outwash sediments transported by interflows were rapidly deposited the inner bay remained under the influence of one or more remnant ice centres until 10 000 bp with ice positioned on the bonavista and gander peninsulas normal marine conditions were established in the outer bay by

winter to winter recurrence of sea surface temperature salinity and mixed layer depth anomalies abstract the mean seasonal cycle of mixed layer depth mld in the extratropical oceans has the potential to influence temperature salinity and mixed layer depth anomalies from one winter to the next temperature and salinity anomalies that form at the surface and spread throughout the deep winter mixed layer are sequestered beneath the mixed layer when it shoals in spring and are then re entrained into the surface layer in the subsequent fall and winter here we document this re emergence mechanism in the north pacific ocean using observed ssts subsurface temperature fields from a data assimilation system and coupled atmosphere ocean model simulations observations indicate that the dominant large scale sst anomaly pattern that forms in the north pacific during winter recurs in the following winter the model simulation with mixed layer ocean physics reproduced the winter to winter recurrence while model simulations with observed ssts specified in the tropical pacific and a 50 m slab in the north pacific did not this difference between the model results indicates that the winter to winter sst correlations are the result of the re emergence mechanism and not of similar atmospheric forcing of the ocean in consecutive winters the model experiments also indicate that sst anomalies in the tropical pacific associated with el nino are not essential for re emergence to occur the recurrence of observed sst and simulated sst and sss anomalies are found in several regions in the central north pacific and are quite strong in the northern 50 n part of the basin the winter to winter autocorrelation of sss anomalies exceed those of sst since only the latter are strongly damped by surface fluxes the re emergence mechanism also has a modest influence on mld through changes in the vertical stratification in the seasonal thermocline

anomalous surface currents in the tropical indian ocean an anomalous climate event occurred in 1997 in the indian ocean with severe consequences for the surrounding continental areas in response to an intensification of the trade winds a westward gradient of sst and an anomalous reversal of the eastward surface currents with peak velocity anomalies exceeding 1 m s were evident in boreal autumn a similar but weaker event took place in 1994 in this study we examine the observational record during the 1990s including surface drifter velocities sst and altimeter sea level to confirm these dramatic changes we examine the key momentum balance between wind induced momentum flux and the pressure gradient force as well as the important role of horizontal temperature advection in the mixed layer heat response

determining the extent and nature of mazatzal related overprinting of the penokean orogenic belt in the southern lake superior region north central usa abstract twenty one hornblende and mica 40ar 39ar dates from central and northwest wisconsin usa provide important information on the timing spatial extent and intensity of mazatzal age metamorphism and deformation which overprinted the paleoproterozoic 1870 1820 ma penokean orogenic belt in the southern lake superior region 1760 1750 ma mica plateau ages from bedrock beneath undeformed 1750 1630 ma quartzites are interpreted as the time of lower temperature 300 350 c cooling and crustal stabilization after the penokean orogeny six mica ages from bedrock underlying deformed paleoproterozoic quartzites cluster around 1600 ma 1576 1614 ma the complete absence of 1760 1750 ma mica ages beneath regions of deformed quartzites suggests widespread heating to temperatures above 300 350 c during mazatzal related deformation and metamorphism the 1600 ma mica ages are interpreted to date the cooling phase of this metamorphism two anomalously young biotite dates are interpreted to indicate partial resetting associated with mesoproterozoic rifting at 1100 ma ten hornblende 40ar 39ar dates obtained in this study address the higher temperature overprinting effects in the southern lake superior region one latest archean age of 2503 18 ma and two ages of 1853 and 1830 ma are interpreted as remnant evidence of archean and penokean age amphibolite metamorphic events respectively the majority of hornblende ages are younger than the penokean orogeny scattering between 1796 and 1638 ma microtextural analysis indicates that similar microstructures exist in samples yielding highly discordant hornblende ages this suggests that shearing and recrystallization did not play an important role in the retention or loss of argon the 1638 ma hornblende age is concordant with the mazatzal orogeny to the south and is interpreted as representing complete thermal or fluid related resetting associated with that event six other post penokean ages scatter over a 70 million year interval 1796 1723 ma and probably reflect variable retention of radiogenic argon they are interpreted to indicate variable degrees of partial intermediate temperature 350 500 c resetting of hornblende argon systematics at 1650 1630 ma collectively these data suggest that the effects of the mazatzal orogeny in the southern lake superior region involved 350 500 c metamorphism and penetrative deformation

the reemergence of sst anomalies in the north pacific ocean abstract sea surface temperature sst data and two different upper ocean temperature analyses are used to study the winter to winter recurrence of sst anomalies in the north pacific ocean the ssts recur when temperature anomalies that form in the deep ocean mixed layer in late winter early spring are isolated from the atmosphere in the summer seasonal thermocline and then reemerge at the surface when the mixed layer deepens during the following fall winter this reemergence mechanism is evaluated over the basin by correlating the time series of the leading pattern of ocean temperature anomalies in the summer seasonal thermocline 60 85 m in august september with sst anomalies over the course of the year the results indicate that the dominant large scale sst anomaly pattern that forms in the north pacific during late winter with anomalies of one sign in the central pacific and the opposite sign along the coast of north america is sequestered in the seasonal thermocline in summer and returns to the

simultaneous inversion for 3 d crustal structure and hypocentres including direct refracted and reflected phases iii application to the southern rhine graben seismic region germany summary the new technique of simultaneous inversion for hypocentres and crustal structure ssh is applied to the southern rhine graben p and s wave first and later arrival times of direct refracted and reflected phases of 350 seismic events are used in the study substantial improvements of over 100 per cent in the non linear residual fit are obtained for the 3 d and less for the 1 d models many of the structural results of the 3 d ssh models are consistent with major findings from other seismic refraction experiments and fit into the general geological petrological and geodynamica1 frame of this area thus the thick sedimentary layer in the rhine graben proper manifests itself by large negative seismic velocity anomalies for the middle crust the ssh models show a strong seismic differentiation between sections of the graben proper and the areas under its western and eastern shoulders of the vosges and the black forest respectively using a new a priori bayesian inversion technique it has been attempted to substantiate the refraction seismic low velocity zone of gajewski prodehl 1987 in the middle crust under the black forest the results demonstrate that such a velocity low is compatible with the observed traveltimes only if one assumes it as a more local crustal phenomenon in this area in the lower crust the ssh models are able to clarify some controversies from earlier refraction experiments in the region the models reveal many seismic features which are typical for continental rift zones such as high transitional velocity anomalies 7 4 km s l under parts of the graben proper rift cushion in the upper mantle the models show a ring like high velocity structure of 8 30 8 40 km s l centred around a low velocity area 7 9 km s l beneath the kaiserstuhl i conjecture this to be a thermal fingerprint of a partially molten upwelling asthenospheric diapir bulging under the moho the simultaneously relocated hypocentres for the 1 d models show some systematic downward movements for the events in the lower crust of the southern black forest area but otherwise do not differ too much from the initial ones to alter the present seismotectonic picture of the southern rhine graben thus the hypothesized phenomenon of the seismic gap along the southern section of the graben black forest wedge can both structurally and seismically be substantiated the relocated hypocentres suggest optically even a widening of this seismic gap the later has thus to be accepted as a possibly more general characteristic of a graben formation

a comparison of mixed layer dynamics between the arabian sea and bay of bengal one dimensional model results 1 using a one dimensional turbulent closure model we investigate the physical mechanisms governing the seasonal evolution of mixed layer depth mld and sea surface temperature sst along two meridional sections 64 5 e and 88 5 e which are representative of the open ocean conditions of the arabian sea and the bay of bengal several perturbation experiments have been performed to isolate and judge exactly the relative importance of wind stress and buoyancy forcing to the evolution of mld and sst the wind stress forcing is found to be significant during the summer monsoon while buoyancy flux plays a significant role during the winter monsoon during the summer monsoon june september the mld in the arabian sea deepens to 80 m owing to strong wind driven vertical mixing but the weaker winds over the bay of bengal restrict the turbulent mixing to a shallow depth of 30 m as a result sst in the arabian sea bay of bengal decreases to 27 c remains high 29 c it is thus the asymmetry in the wind field that is responsible for the difference in mld and sst between the arabian sea and the bay of bengal during the winter monsoon november february the mld in the arabian sea penetrates to deeper than 80 m by convective vertical mixing because of strong negative buoyancy flux net heat loss but it is restricted to 40 50 m in the bay of bengal owing to reduced net heat loss from the ocean it is the asymmetry in the buoyancy forcing caused by the difference in latent heat flux that is responsible for the difference in mld and sst between the arabian sea and the bay of bengal the atmospheric parameter that controls this buoyancy difference is the difference in humidity between the two basins thus it is the differences in surface forcing rather than differences in the vertical salinity stratification that are key in explaining the observed and modeled differences between the arabian sea and bay of bengal

an 40 ar 39 ar investigation of the contact effects of a dyke intrusion kapuskasing structural zone ontario an 40ar 39ar study on biotite and hornblende from baked tonalite gneiss adjacent to a 14 m wide kapuskasing dyke in the chapleau block of the kapuskasing structural zone employed resistance furnace step heating of bulk mineral separates single grain laser step heating and laser spot dating of individual grains in thick section all three methods yielded concordant results for the biotite indicating that it has been uniformly overprinted at ca 2 05 ga this date is probably a close estimate of the age of the dyke intrusion the argon data from the hornblende are more difficult to interpret all three methods suggest that the hornblende was partially overprinted and then affected by a later influx of excess argon from the external environment laser spot dates record an apparent age gradient extending radially outward from 2 25 ga in the grain cores to 2 4 2 7 ga in the grain rims corresponding 37ar 39ar values show no systematic variation across the hornblende although 38ar 39ar ratios display a similar pattern to the age distribution with lower values in the cores than in the rims the bulk separate and single grain step heating spectra mimic a volume diffusion ar loss profile that would appear to be inconsistent with the laser spot dates three possible interpretations to explain this apparent discrepancy may involve either experimental difficulties an effective radius of diffusion which is much smaller than the actual grain radius or an effective radius of diffusion that is of the order of the grain radius it is clear that for the 40ar 39ar dating of samples that have experienced complex geologic histories it is important to utilize both resistance furnace and laser techniques

recent shifts in the state of the north pacific 1 the winters of 1999 2002 for the north pacific were characterizedbyspatialpatternsinsealevelpressureanomaly slpa and sea surface temperature anomaly ssta with little resemblance to those of the leading pattern of north pacific climate variability the pacific decadal oscillation pdo in essence the southeastern northern portion of the north pacific was subject to atmospheric forcing characteristic of that before after the major regime shift of 1976 77 recent major changes in the ecosystems off the west coast of the united states and continued conditions similar to those of the early 1990s in the gulf of alaska bering sea and sea of okhotsk are consistent with these slpa and ssta patterns our result illustrates that a single indicator such as the pdo is incomplete in characterizing north pacific climate index terms 1635 global change oceans 4203 1610 global change atmosphere 0315 0325 4215 oceanography general climate and interannual variability 3309 3339 meteorology and atmospheric dynamics ocean atmosphere interactions 0312 4504 citation bond n a j e overland m spillane and p stabeno recent shifts in the state of the north pacific geophys res lett 30 23 2183 doi 10 1029 2003gl018597 2003

variability of the oceanic mixed layer 1960 2004 abstract a new monthly uniformly gridded analysis of mixed layer properties based on the world ocean atlas 2005 global ocean dataset is used to examine interannual and longer changes in mixed layer properties during the 45 yr period 1960 2004 the analysis reveals substantial variability in the winter spring depth of the mixed layer in the subtropics and midlatitudes in the north pacific an empirical orthogonal function analysis shows a pattern of mixed layer depth variability peaking in the central subtropics this pattern occurs coincident with intensification of local surface winds and may be responsible for the sst changes associated with the pacific decadal oscillation years with deep winter spring mixed layers coincide with years in which winter spring sst is low in the north atlantic a pattern of winter spring mixed layer depth variability occurs that is not so obviously connected to local changes in winds or sst suggesting that other processes such as advection are more important interestingl

gravity and height variations connected with the current rifting episode in northern iceland abstract following a first gravity survey in 1938 high precision gravity measurements with lacoste romberg gravimeters have been carried out in northern iceland in 1965 1970 1971 and 1975 in order to detect eventual secular gravity variations at that supramarine part of a constructive plate boundary since 1975 when an active rifting episode started there gravity and height variations have been observed in annual intervals these surveys concentrated on the approx 100 km long and 5 km wide fissure zone associated with the krafla central volcano which is the center of the present activity the observations which have been performed at an accuracy level of 0 01 mgal resp 0 03 m give significant information about the long term behaviour of the vertical mass shifts occuring during the rifting process a steep gravity variation gradient observed south of the krafla caldera between 1965 and 1975 may be interpreted as some kind of precursor of the current process since 1975 the rifting event is characterized by shifting activity areas with gravity decrease and elevation at the flanks and gravity increase and subsidence at narrow central parts of the krafla fissure zone the annual variations reaching 0 1 mgal resp 0 5 m and more since 1978 the activity has concentrated on the gjastikki region north of the krafla volcano with decreasing variations in the southern and northern parts of the fissure swarm the average gravity height variation ratio calculated for two profiles south and north of krafla over the observation periods between 1975 and 1979 amounts to 0 2 mgal m but extreme values are found at recently activated areas

millennial scale variations of the holocene north atlantic mid depth gyre inferred from radiocarbon and neodymium isotopes in cold water corals abstract variations in north atlantic ocean mid depth circulation during the holocene are poorly understood it is believed that they had a significant influence on the properties of water entering the nordic sea by redistributing heat and freshwater potentially affecting deep water formation and climate to improve our knowledge of the ne atlantic mid depth circulation radiocarbon and neodymium isotope analyses have been then carried out on precisely dated u th l pertusa and m oculata coral fragments from two sediment cores taken at 750 m water depth on the sw rockall trough margin cold water coral cwc end values vary between 12 2 0 3 and 16 6 0 4 and result from variable contributions of unradiogenic mid depth subpolar gyre mid spg water 15 and more radiogenic eastern north atlantic water enaw 11 which is transported northward to the rockall trough by boundary currents along the european margin increased coral end reflects a westward contraction of the mid spg water and a higher proportion of enaw the mid holocene from 8 8 to 6 8 ka bp is marked by unradiogenic coral end from 16 6 0 4 to 14 6 0 5 indicating a greater eastward extension of the mid spg this is followed by a shift from 6 8 to 5 ka bp toward more radiogenic end values from 15 4 0 3 to 13 3 0 2 suggesting a westward contraction of the mid spg and a higher proportion of enaw the mid holocene long term change in end is characterized by millennial variations of up to 2 5 epsilon units well marked during the late holocene indicating that eastward extension of the mid spg coeval with warm periods in northern europe e g the medieval climatic anomaly and the roman warm period most of the cwc derived 14c values match the global ocean values indicating that the water masses bathing the corals were generally well ventilated the exceptions are a few short intervals of eastward extension of the mid spg which are characterized by lower 14c during the late holocene we propose that these minor 14c fluctuations in the rockall trough may be related to local changes in the mixed layer depth or to variability in the advection of water from the labrador sea where deep convection gives rise to thermocline waters that are relatively depleted in terms of 14c the eastward extension of the mid spg between 8 8 and 6 8 ka bp is associated with the holocene climatic optimum concurrent with a maximum strength of the iceland scotland overflow water isow which is indicative of an increase in the atlantic meridional overturning circulation amoc this period is followed by a transition in the north atlantic circulation which occurred around 6 8 ka bp and coincides with the onset of labrador sea water formation a decrease of the isow strength and a contraction of the mid spg leading to a greater intrusion of saline subtropical water into the subpolar atlantic

brine rock interaction in the athabasca basement mcarthur river u deposit canada consequences for fluid chemistry and uranium uptake terra nova 22 303 308 2010 abstract the nature of uranium source rocks transport conditions and deposition processes are still highly controversial for world class unconformity related u deposits this article presents the first detailed chemistry of brines associated with the giant mcarthur river u deposit canada la icp ms analysis of individual fluid inclusions suggests mixing between a na ca mg k sr ba brine and a ca mg na k sr ba brine the brines share a common origin evaporated seawater and show evidence for contrasting interaction with basement rocks the na rich brine lost mg and k in alteration haloes around u ores while the ca rich brine results from na ca exchange and sr ba gain u concentrations 0 3 530 g g 1 are anomalously high compared with usual basinal fluids this indicating that u uptake occurred within basement rocks the two brine end members have mixed within the main u deposit area which could be one of the major driving forces for u deposition

argon retentivity of hornblendes a field experiment in a slowly cooled metamorphic terrane hornblende from samples of amphibolite and granitic gneiss collected within a single outcrop in the central adirondacks yield significantly different sup 40 ar sup 39 ark sub k dates of 948 plus minus 5 and 907 plus minus 5 ma assuming that this terrane cooled slowly following high grade metamorphism and that the samples have experienced the same thermal history the difference in dates apparently reflects a corresponding difference in blocking temperature for diffusion of radiogenic argon in these hornblende samples the fe fe mg mn of the hornblende samples are 0 8 and 0 6 the higher ratio corresponding to the younger sup 40 ar sup 39 ar sub k date transmission electron microscopy observations indicate that both hornblende samples are homogeneous and devoid of any exsolution but contain zones of fibrous phyllosilicates approximately 0 1 to 2 mu m wide parallelling 100 and 110 these alteration zones probably formed during post metamorphic cooling as a result of the migration of fluids through the hornblendes and are obvious pathways for argon escape from hornblende as these features are more abundant in the hornblende sample with the younger sup 40 ar sup 39 ar date and higher fe fe mg mn they may influence the argon blocking temperature by effectively partitioning the hornblende grains intomore diffusion domains of varying size biotite from the granitic gneiss yields an sup 40 ar sup 39 ar sub k date of 853 plus minus 2 ma with a mildly discordant step heating spectrum that in part reflects the degassing of submicroscopic inclusions precipitated during alteration of the host biotite plagioclase from the amphibolite yields a sup 40 ar sup 39 ar sub k integrated date of 734 plus minus 3 ma less

subduction of decadal north pacific temperature anomalies observations and dynamics abstract observations of oceanic temperature in the upper 400 m reveal decadal signals that propagate in the thermocline along lines of constant potential vorticity from the ventilation region in the central north pacific to approximately 18 n in the western pacific the propagation path and speed are well described by the geostrophic mean circulation and by a model of the ventilated thermocline the approximate southward speed of the thermal signal of 7 mm s 1 yields a transit time of approximately eight years the thermal anomalies appear to be forced by perturbations of the mixed layer heat budget in the subduction region of the central north pacific east of the date line a warm pulse was generated in the central north pacific by a series of mild winters from 1973 to 1976 and reached 18 n around 1982 after 1978 a succession of colder winters initiated a cold anomaly in the central north pacific that propagated along a similar path and with a similar speed as the warm anomaly then arrived in the west

determination of vertical recent crustal movements by levelling and gravity data abstract recent vertical crustal movements are generally studied by comparing either repeated levellings or repeated gravity measurements neither of these procedures gives strictly true vertical displacements of points a theoretically more satisfactory approach can be based on a stokes like integral formula requiring both types of data assuming a constant linear relationship between temporal changes of gravity and temporal changes of levelled heights in an area of interest two variants of the original integral formula are derived either variant requiring essentially only one type of data the first variant can be used if besides extended repeated levellings the constants of the linear relationship are available by using both types of data on some common points equivalently the second variant is based on repeated gravity measurements both variants contain a small surface integral term which is numerically estimated by model computations finally the theory is applied to the determination of real crustal movements in western hokkaido japan the temporal changes of gravity and of height at twenty points gave a correlation coefficient 0 66 which is statistically significant at the 1 per cent level neglecting the temporal changes of geoid undulations could cause systematic errors in indicated recent crustal movements in the area reaching the magnitude of one standard deviation of the relative height of the extreme points in the area further numerical investigations require the collection of precise data at some geodynamic test areas

tectonic evolution of proterozoic australia proterozoic australia has long been interpreted as a single intact continent in which all tectonic and magmatic activity was intracratonic this paper proposes an alternative hypothesis in which numerous fragments of continental crust were assembled by plate tectonic processes the assembly was completed between 1300 and 1100 ma when the crustal fragments were combined as an early component of the rodinian supercontinent rifting and fragmentation of archaean continents began in the late archaean and continued into the proterozoic passive margin deposits such as those of the hamersley basin accumulated on isolated fragments of archaean crust these numerous fragments were subsequently assembled into three cratons by 1830 ma a west australian craton was established by collision of the archaean pilbara and yilgarn cratons which were joined along the capricorn orogen similarly a south australian craton developed by amalgamation of the proto gawler and proto curnamona cratons along the kimban orogen a north australian craton appears to have formed by accretion of numerous crustal fragments including the kimberley pine creek lucas and altjawarra cratons with sutures marked by the king leopold halls creek tennant creek and proto isan orogens the southern margin of the north australian craton was the site of repeated terrane accretion and orogenic activity between 1880 ma and 1400 ma this included an orogenic event at 1880 1850 ma the strangways 1780 1730 ma argilke 1680 1650 ma and chewings 1620 1580 ma orogenies and the intracratonic anmatjira uplift 1500 1400 ma intracratonic rifting at 1750 to 1710 ma and 1640 to 1600 ma produced the mcarthur basin and related minor basins parts of which were deformed by the isan orogeny at 1600 and 1530 ma rifting along the line of the capricorn orogen led to deposition in the overlying intracratonic bangemall basin between 1630 and 1300 ma along the eastern margin of the south australian craton the 1670 to 1600 ma olarian orogeny marks interaction with now obscured continental crust to the east tectonic activity between 1300 and 1100 ma led to the assembly of proterozoic australia as an early component of the supercontinent of rodinia this first involved the amalgamation of the west australian and north australian cratons followed by collision with the south australian craton the centralian superbasin developed over the junction of the north south and west australian cratons between 830 and 750 ma rifting to the east formed the adelaide geosyncline at 830 ma this was followed by the breakup of rodinia with the rifting apart of laurentia and gondwanaland along the eastern margin of proterozoic australia at 750 ma and the subsequent formation of the palaeo pacific ocean after the breakup of rodinia a series of northeast southwest compressional events followed by periods of relaxation reflect the assembly of a new supercontinent old lines of weakness were reactivated culminating in the intracratonic king leopold paterson petermann ranges and pinjarra orogenies between 620 and 540 ma subsequent reactivation continued into the phanerozoic with the widespread eruption of continental flood basalts and the formation of intracratonic basins 540 530 ma

rapid freshening of the deep north atlantic ocean over the past four decades the overflow and descent of cold dense water from the sills of the denmark strait and the faroe shetland channel into the north atlantic ocean is the principal means of ventilating the deep oceans and is therefore a key element of the global thermohaline circulation most computer simulations of the ocean system in a climate with increasing atmospheric greenhouse gas concentrations predict a weakening thermohaline circulation in the north atlantic as the subpolar seas become fresher and warmer1 2 3 and it is assumed that this signal will be transferred to the deep ocean by the two overflows from observations it has not been possible to detect whether the ocean s overturning circulation is changing but recent evidence suggests that the transport over the sills may be slackening4 here we show through the analysis of long hydrographic records that the system of overflow and entrainment that ventilates the deep atlantic has steadily changed over the past four decades we find that these changes have already led to sustained and widespread freshening of the deep ocean

ocean mixed layer processes in the pacific decadal oscillation in coupled general circulation models it is investigated how the pacific decadal oscillation pdo is simulated differently among various coupled general circulation models cgcms and how it is related to the heat budget of the simulated ocean mixed layer which includes the surface heat flux and ocean heat transport for this purpose the dataset of the climate of the 20th century experiment 20c3m from nine cgcms reported to ipcc s ar4 are used while the mri and miroc models are examined in detail detailed analyses of these two cgcms reveal that the pdo is mainly affected by ocean heat transport rather than surface heat flux in particular in the mri model which has a larger contribution of ocean heat transport to the heat budget it is found that the ocean heat transport due to ekman advection versus geostrophic advection contributes differently to the pdo in the western and central north pacific specifically the strength of pdo tends to be larger for cgcms with a larger ocean heat transport in the region

late paleoproterozoic climate tectonics and metamorphism in the southern lake superior region and proto north america evidence from baraboo interval quartzites abstract red supermature quartzites of the baraboo interval of the lake superior region contain detrital zircon that ranges in age from 1782 to 1712 ma deposition clearly occurred after the geon 18 penokean orogeny these late paleoproterozoic sedimentary rocks consist largely of quartz kaolinite or pyrophyllite and hematite detrital feldspar and muscovite are rare or absent their chemical index of alteration ranges from 96 8 to 98 6 among the most chemically mature clastic sediments in the geological record the quartzites are underlain by mature feldspar free paleosols accounting for the absence of feldspar in the overlying sediments and indicating the presence of first cycle quartzose detritus such physical and chemical characteristics imply that late paleoproterozoic deposition in the lake superior region occurred in a stable tectonic setting with subdued topographic relief in a warm humid climate folding and low grade metamorphism of the quartzites is thought to reflect 1630 ma foreland

the north atlantic oscillation surface current velocities and sst changes in the subpolar north atlantic changes in surface circulation in the subpolar north atlantic are documented for the recent interannual switch in the north atlantic oscillation nao index from positive values in the early 1990s to negative values in 1995 96 data from lagrangian drifters which were deployed in the north atlantic from 1992 to 1998 were used to compute the mean and varying surface currents ncep winds were used to calculate the ekman component allowing isolation of the geostrophic currents the mean ekman velocities are considerably smaller than the mean total velocities that resemble historical analyses the northeastward flow of the north atlantic current is organized into three strong cores associated with topography along the eastern boundary in rockall trough in the iceland basin the subpolar front and on the western flank of the reykjanes ridge irminger current the last is isolated in this eulerian mean from the rest of the north atlantic current by a region of weak velocities on the east side of the reykjanes ridge the drifter results during the two different nao periods are compared with geostrophic flow changes calculated from the nasa pathfinder monthly gridded sea surface height ssh variability products and the advanced very high resolution radiometer avhrr sst data during the positive nao years the northeastward flow in the north atlantic current appeared stronger and the circulation in the cyclonic gyre in the irminger basin became more intense this was consistent with the geostrophic velocities calculated from altimetry data and surface temperature changes from avhrr sst data which show that during the positive nao years with stronger westerlies the subpolar front was sharper and located farther east sst gradients intensified in the north atlantic current irminger basin and east of the shetland islands during the positive nao phase associated with stronger currents sst differences between positive and negative nao years were consistent with changes in air sea heat flux and the eastward shift of the subpolar front sst advection as diagnosed from the drifters likely acted to reduce the sst differences

on the reemergence of north atlantic sst anomalies abstract the reemergence mechanism whereby temperature anomalies extending over the deep winter mixed layer are stored beneath the surface in summer and are reentrained into the mixed layer when it deepens again in the following autumn and winter is studied in the north atlantic using approximately 40 years of surface and subsurface data reemergence is found to be robust in the sargasso sea and the northeast atlantic regions where i the mixed layer is much deeper in winter than in summer ii currents are relatively weak and iii temperature anomalies are coherent over broad areas the two leading empirical orthogonal functions of north atlantic sst anomalies also exhibit strong reemergence signatures a novel application of empirical orthogonal function analysis to temperature anomalies in the time depth plane which also incorporates information from all grid points is shown to be an efficient and useful approach for detecting reemergence without dependence on specific spatial patterns or prio

filling the north american proterozoic tectonic gap 1 60 1 59 ga deformation and orogenesis in southern wyoming usa abstract structural and thermochronologic studies in the sierra madre southern wyoming indicate that parts of the 1 78 1 75 ga cheyenne belt an archean proterozoic suture were reactivated at ca 1 6 ga new shear zones notably the brittle battle lake thrust tear fault zone also formed at this time the battle lake fault zone blfz which displaced parts of the cheyenne belt at least 30 km to the north corresponds to the surface expression of a south dipping reflector imaged by regional seismic studies continental dynamics of the rocky mountains experiment 40ar 39ar and u pb data define age patterns in the sierra madre that are delineated by discrete structures north of the 1 78 ga divide peak mylonite zone a foreland structure associated with the medicine bow orogeny 40ar 39ar biotite dates suggest cooling below 300 c by 2 0 ga south of the divide peak mylonite zone but north of the blfz hornblendes yield apparent 40ar 39ar ages of ca 1 80 1 78 ga that may record tectonic burial and cooli

a regional index of northeast pacific variability based on satellite altimeter data 1 an index of climate variability to monitor the state of the upper ocean is proposed for the northeast ne pacific ocean based on sea surface height ssh data from satellite altimetry while sea surface temperature sst is often used characterize ocean variability ssh reflects the integrated influence of temperature and salinity anomalies through the water column a canonical correlation analysis shows that ssh and sst anomalies vary coherently at large spatial scales and low frequencies over the region ssh anomalies are less subject to short period variability and the temporal components for ssh resemble smoothed low pass filtered versions of the sst components also examined is the relationship between the sst based pacific decadal oscillation pdo index and the large scale upper ocean variability reflected in the leading principal component of ssh anomalies the comparison demonstrates that the ssh principal component provides a robust index of regional climate variability that is less noisy than the pdo the results are used to examine the 1998 2002 climate event over the ne pacific

key controls on the seasonal and interannual variations of the carbonate system and air sea co2 flux in the northeast atlantic bay of biscay 1 biogeochemical variations of surface water in the northeast atlantic bay of biscay were examined using high frequency underway measurements combined with monthly sampling of carbon related variables the mechanisms controlling seasonal co2 variability were investigated by distinguishing the contributions of biological and physical processes to the monthly changes in dissolved inorganic carbon dic and partial pressure of co2 pco2 the seasonality of dic 47 81 mol kg 1 had a single peak with a winter maximum primarily driven by vertical mixing and a summer minimum driven by spring biological removal non redfield c n uptake was observed in the nutrient depleted summer but not during the spring bloom in the north atlantic pco2 seasonality shows a latitudinal transition from the temperature dominated oligotrophic subtropical gyre to the subpolar region where pco2 is dominated by changing concentrations of dic in the midlatitude bay of biscay the annual cycle of pco2 61 75 atm showed a double peak distribution the summer pco2 peak was mainly driven by temperature increase while the winter peak resulted from the dominant effect of entrainment of subsurface water interannual variations of dic were more pronounced in winter and were driven by the changes in the strength of winter mixing higher wintertime concentrations and seasonal amplitudes of dic were observed in cold years when the mixed layer depths were deeper which appears to be associated with negative phases of the north atlantic oscillation the bay of biscay shows a decrease of co2 uptake in 2008 2010 0 97 and 0 75 mol m 2 yr 1 compared to 2002 2004 1 47 and 1 68 mol m 2 yr 1

the age of unconformity related uranium mineralization in the athabasca basin northern saskatchewan age data are presented for major athabasca basin uranium deposits at cigar lake cluff lake collins bay dawn lake eagle point mcarthur river midwest and rabbit lake as well as for several minor or undeveloped deposits including hughes lake and nisto the best constrained data indicate that almost all the deposits formed in a restricted time interval between about 1330 and 1380 ma this range of ages is believed to be real and not the result of uncertainties in the calculation of ages based on discordant data the one major exception is the recently discovered nias free deposit at mcarthur river for which a well determined age of 1514 18 ma 2 has been obtained even this deposit yields an age in the1330 1380 ma range for some material periods of reworking redeposition occurred at 1280 1000 575 and 225 ma these may be basin wide affecting to some degree all the deposits that we have studied other times of redeposition are less well determined but may be present as well no ages tha

geochemistry of uraniferous bitumen in the southwest athabasca basin saskatchewan canada the sediment hosted unconformity type southwest athabasca uranium mineralization in northern saskatchewan canada contains uraniferous bitumen as observed elsewhere in the athabasca basin uraninite is present either as micron sized grains dispersed in bitumen uraniferous bitumen or as larger grains situated in the pore space between bitumen globules the spatial and textural relationships between uraninite and bitumen suggest that they were co precipitated la icp ms u pb dating of uraniferous bitumen yielded an age of 1575 53 ma similar to that of other unconformity type uranium mineralization in the athabasca basin indicating that the bitumen was formed early in the history of the basin nitrogen carbon and sulfur isotope analyses of uraniferous bitumen indicate that its source material was probably kerogen produced by cyanobacteria in a clastic environment

el nino variability in simple ocean data assimilation soda 1871 2008 1 a new ocean reanalysis that covers the period from 1871 to 2008 is used to explore the time evolving characteristics of el nino the new reanalysis assimilates all available hydrographic and sea surface temperature data into a model of the global ocean forced with surface boundary conditions from an atmospheric reanalysis that also covers the period from 1871 through 2008 using traditional measures of el nino our reanalysis shows that the timing of el nino events is in agreement with sea surface temperature reconstructions but el nino in the reanalysis is stronger particularly from 1871 to 1920 a new index based on the first moment of the temperature anomaly is introduced the new index is used to characterize the strength and location of el nino events and has the advantage that it is independent of the location of el nino using the new index el nino in the reanalysis shows prominent decadal variability of strength but relatively little long term trend el nino events were strong in the last part of the 19th century and first part of the 20th century and again in the latter part of the 20th century with weak el nino events in the middle of the 20th century the location of el nino also varies considerably ranging from the western to the eastern pacific near the coast of south america however the null hypothesis that the location of el nino can be represented as a random distribution about a central longitude of about 140 w cannot be rejected

hydrothermal rare earth element xenotime mineralization at maw zone athabasca basin canada and its relationship to unconformity related uranium deposits a reply

barrier layers in the tropical south atlantic mean dynamics and submesoscale effects abstractbarrier layers are generated when the surface mixed layer is shallower than the layer where temperature is well mixed in geographical regions where salinity plays a key role in setting up upper ocean density stratification in the tropical oceans thick barrier layers are also found in a latitude range where spiraling trajectories from surface in situ drifters suggest the presence of predominantly cyclonic submesoscale like vortices the authors explore these dynamical processes and their interplay in the present paper focusing on the tropical south atlantic ocean and using a high resolution modeling approach the objective is threefold to investigate the mean dynamics contributing to barrier layer formation in this region to study the distribution and seasonality of submesoscale features and to verify whether and how the submesoscale impacts barrier layer thickness the model used is the regional ocean modeling system roms in its adaptive grid refinement in fortran agrif online nested co

formation and evolution of the cigar lake uranium deposit based on u pb and k ar isotope systematics a systematic geochronological study was conducted on the cigar lake uranium deposit u pb and pb pb systematics were applied to different types of uranium ore and various associated sheet silicates were dated by the k ar method these two approaches define a widespread retrograde metamorphic event in the basement which occurred at about 1780 ma during the hudsonian orogeny and a four stage evolutionary model for the ore deposit this model is compatible with the history of other unconformity type uranium deposits in the athabasca basin the first stage in the evolution of the cigar lake uranium deposit is marked by uraninite crystallization at 1341 17 ma which in association with arsenides and sulpharsenides constitutes the mineralization of economic interest main orebody the second stage characterized by a fe kaolinite and fe illite paragenesis occurred locally at about 900 ma the third stage involved uranium mobilization at about 325 ma and is characterized by i preferential loss of radi

gravimetry for monitoring vertical crustal movements potential and problems abstract through recent developments in absolute and relative techniques gravimetry has reached an accuracy of a few hundredths to a few tenths of m s 2 in small or large scale networks respectively consequently gravimetric techniques can now be employed as one efficient tool for detecting vertical crustal movements gravity data are necessary for converting the results of geometric levelling to heights defined in the gravity field and by repeated surveys to control time variations of the height reference surface more important is the use of repeated gravity surveys for strengthening and partly replacing levelling being a time consuming procedure with unfavourable error propagation over larger distances the successful application of observed gravity variations with time in the detection of vertical crustal movements depends on the reliability of the conversion factor between gravity and height changes and on the accuracy of the gravity measurements the conversion factor should be determined through simultaneous levelling and gravimetry in representative parts of the survey region strategies for establishing gravimetric control are changing now with the availability of transportable absolute gravity meters and the possibility of accurately calibrating relative instruments and observing small gravity differences with feed back systems consequently more attention has to be given now to disturbing effects of environmental character such as microseismics atmospheric pressure and groundwater table variations and to periodic effects such as gravimetric earth tides and polar motion

linear trends in salinity for the world ocean 1955 1998 1 quality controlled oceanographic profile salinity measurements from the world ocean database 2001 wod01 were used to calculate linear trends of zonally averaged salinity anomalies for running five year periods from 1955 1959 through 1994 1998 for the world ocean and the atlantic pacific and indian ocean basins from the surface to 3000 meters depth each basin exhibits large scale coherent trends most of the pacific is freshening with the exception of the subtropical south pacific the atlantic exhibits a deep freshening in the subpolar gyre and a shallower more intense increase in salinity in the tropics and subtropics the indian ocean is becoming more saline at all latitudes in the upper 150 meter layer with a subsurface freshening between 40 s and the equator in the 250 1000 meter layer there is freshening in both the weddell and ross seas

vertical datum unification for the international height reference system ihrs the international association of geodesy released in july 2015 a resolution for the definition and realisation of an international height reference system ihrs according to this resolution the ihrs coordinates are potential differences referring to the equipotential surface of the earth s gravity field realised by the conventional value w0 62 636 853 4 m2s 2 a main component of the ihrs realisation is the integration of the existing height systems into the global one i e existing vertical coordinates should be referred to one and the same reference level realised by the conventional w0 this procedure is known as vertical datum unification and its main result are the vertical datum parameters i e the potential differences between the local and the global reference levels in this paper we rigorously derive the observation equations for the vertical datum unification in terms of potential quantities based on the geodetic boundary value problem gbvp approach those observation equations are then empirically evaluated for the vertical datum unification of the north american and south american height systems in the first case simulations performed in north america provide numerical estimates about the impact of omission errors and direct and indirect effects on the vertical datum parameters in the second case a combination of local geopotential numbers itrf coordinates satellite altimetry observations tide gauge registrations and high resolution gravity field models is performed to estimate the level differences between the south american height systems and the global level w0 results show that indirect effects vanish when a satellite only gravity field model with a degree higher than n 180 is used for the solution of the gbvp however the component derived from satellite only global gravity models has to be refined with terrestrial gravity data to minimise the omission error and its effect on the vertical datum parameter estimation the empirical evaluations demonstrate that the vertical datum unification should be based on geodetic stations of highest quality and standardised geodetic data for example geometric coordinates should refer to the same itrf and be given in the same tide system and reference epoch as the geopotential numbers and gravity field model after a standardisation of the input data used in the unification of the south american height systems and a rigorous error propagation analysis we demonstrate that the vertical datum parameters can be estimated with accuracy better than 5 cm in well surveyed regions and some decimetres 40 cm in sparsely surveyed regions this paper concludes with detailed guidelines for the appropriate data treatment when the integration of a local vertical datum into the ihrs is desired these guidelines may be applicable in any region of the world