testing the reliability of discrimination diagrams for determining the tectonic depositional environment of ancient sedimentary basins the lower palaeozoic rocks of the west of ireland caledonides provide a novel way to test the reliability of discrimination diagrams in sedimentary rocks a comparison between the geochemical signature of the tuff bands and the signature from the adjacent sedimentary rocks reveals that a combination of multi element diagrams and discrimination diagrams is best suited to identify the tectonic environment of deposition the tuff bands from the ordovician and silurian formations all carry an active continental margin signature only three of the sedimentary discrimination diagrams assigned more than 50 of the samples to this setting the results from the discrimination diagrams indicate an active margin setting for the ordovician mweelrea and rosroe formations and the silurian formations whilst the derrylea and sheeffry sedimentary samples have a passive margin signature overall the results show that in the case where felsic volcanism occurred on a quartz rich source region the active continental margin field on many established discrimination diagrams is not reliable in identifying this setting however the study highlights one of the key strengths of discrimination diagrams in their ability to be used as a lever to reveal significant information about the sediment source as in this case to identify sediment that has been transported from different tectonic settings and deposited in one sedimentary basin

early diagenesis in differing depositional environments the response of transition metals in pore water the cycling of fe mn ni co cu cr v and mo during early diagenesis was investigated in sediments from five different depositional environments in the california borderland dissolved o2 no3 no2 and so4 were also measured at each site to establish the position of redox boundaries pertinent to this study sites were chosen to allow the comparison of several parameters of potential importance to the cycling of these metals bottom water o2 concentration sediment redox conditions cycling of metal oxide carrier phases and the relative contribution of biogenic and terrigenous material to the detrital metal flux at 10 m oxygen and above the sequence of terminal electron acceptor utilization was typical of pelagic sediments differing only in scale under these conditions the recycling of mn oxides resulted in an enriched layer near the interface at bottom water 02 concentrations 5 m mn oxides are not recycled under these conditions fe oxides and so42 are important oxidants the depth of the zone of manganese oxidation with respect to the interface affects the efficiency of metal scavenging by manganese oxides trapping and recycling of ni and co with mn oxides results in remobilization from reducing sediments and enrichment in oxic sediments scavenging of these metals is favored by a deep oxic zone in the sediments in contrast cr v and mo appear to be transported to the sediments as reduced species and are released from the sediments by oxidation the source of the reduced species is assumed to be biogenic material the accumulation of these metals is favored by reducing conditions in the sediments cu is enriched in the sediments by transport with detrital biogenic material followed by adsorption onto sediment solids cu is released at the interface and rapidly removed onto the solids at all sites except the one pelagic site at the base of the slope the magnitude of cu released in the slowly accumulating pelagic sediment exceeds the cu binding capacity of the solids resulting in pore water cu concentrations in excess of 100 nm in general metal cycling associated with the early diagenesis of sediments was observed to decouple transport processes from burial processes for the transition metals measured in this study

exhumation of eclogites insights from depth time path analysis abstract literature data on geochronology and pressure temperature estimates have been used to assess the depth time paths for high pressure units in the alps and the variscan belt these depth time paths consistently show that exhumation rates decrease through time the first stages of the exhumation are rapid 1 mm yr 1 and last less than a few million to a few tens of million years in contrast the final 10 20 km ascent to the surface is at least one order of magnitude slower for the deepest and most important part of the exhumation trajectory the chronology of the retrogressive metamorphism excludes gravitational collapse as the major driving force material balance and structural arguments also exclude isostatically assisted erosion processes prism dynamics and tectonically assisted erosion are the most likely mechanisms accounting for the kinetics of exhumation isostasy assisted erosion and shallow level extension are nevertheless required to eventually bring the high pressure rocks to exposure

uranium 236 as a new oceanic tracer a first depth profile in the japan sea and comparison with caesium 137 we present a feasibility study for using 236u as an oceanic circulation tracer based on depth profiles of 236u and 137cs in the japan east sea the concentration of the predominantly anthropogenic 236u measured with accelerator mass spectrometry ams decreased from 13 3 106 atom kg in surface water to 1 6 0 3 106 atom kg close to the sea floor 2800 m the profile has a smooth trend with depth and concentration values are generally proportional to that of 137cs for the same water samples but with a slightly lower ratio of 137cs 236u below 2000 m the cumulative inventory of dissolved 236u in the water column was estimated to be 13 7 0 9 1012 atom m2 which is similar to the global fallout level 17 8 1012 atom m2 in japan additional analyses of suspended solids ss and bottom sediments yielded negligible amounts of 236u our results suggest that 236u behaves as a conservative nuclide in seawater with potential advantages over other tracers of oceanic circulation

assimilation of radiocarbon and chlorofluorocarbon data to constrain deep and bottom water transports in the world ocean a coarse resolution global model with time invariant circulation is fitted to hydrographic and tracer data by means of the adjoint method radiocarbon and chlorofluorocarbon cfc 11 and cfc 12 data are included to constrain deep and bottom water transport rates and spreading pathways as well as the strength of the global overturning circulation it is shown that realistic global ocean distributions of hydrographic parameters and tracers can be obtained simultaneously the model correctly reproduces the deep ocean radiocarbon field and the concentrations gradients between different basins the spreading of cfc plumes in the deep and bottom waters is simulated in a realistic way and the spatial extent as well as the temporal evolution of these plumes agrees well with observations radiocarbon and cfc observations place upper bounds on the northward transports of antarctic bottom water aabw into the pacific atlantic and indian oceans long term mean aabw transports larger than 5 sv sv 10 6 m 3 s 1 through the vema and hunter channels in the south atlantic and net aabw transports across 30 s into the indian ocean larger than 10 sv are found to be incompatible with cfc data the rates of equatorward deep and bottom water transports from the north atlantic and southern ocean are of similar magnitude 15 7 sv at 50 n and 17 9 sv at 50 s deep and bottom water formation in the southern ocean occurs at multiple sites around the antarctic continent and is not confined to the weddell sea a cfc forecast based on the assumption of unchanged abyssal transports shows that by 2030 the entire deep west atlantic exhibits cfc 11 concentrations larger than 0 1 pmol kg 1 while most of the deep indian and pacific oceans remain cfc free by 2020 the predicted cfc concentrations in the deep western boundary current dwbc in the north atlantic exceed surface water concentrations and the vertical cfc gradients start to reverse

cadmium diagenesis in laurentian trough sediments the depth distributions of cd mn and fe in pore water and sediment were determined on three replicate box cores collected at a 325 m deep station in the laurentian trough the results reveal a surface layer in which the content of solid phase cd first decreases but then increases sharply with depth in contrast mn decreases regularly over the same depth interval in the oxygenated zone of this layer cd probably associated with organic matter is released to the pore water resulting in concentrations that are more than an order of magnitude higher than in the overlying water column some of the dissolved cd is returned to the water column and some migrates downward and is precipitated at depth this part of the cd cycle is virtually complete within the surface layer the base of which corresponds to the base of the zone of mn enrichment in the subsurface layer solid phase cd and mn show little or no concentration change however dissolved cd which reaches often non detectable concentrations 0 05 nm in this layer increases once again deep within the anaerobic zone and attains concentrations even higher than in the surface layer the presence of dissolved cd complexes revealed by 1 5 to 8 fold increases in electrochemically active cd in pore water following uv treatment as well as inconsistent distributions of dissolved and solid phase cd indicate complexities in diagenesis that merit further investigation

characteristics and formation of eastern south pacific intermediate water 1 newly gathered hydrographic data from the eastern south pacific is combined with other high quality data mainly woce to reassess the properties and boundaries of the eastern south pacific intermediate water espiw to date the espiw has been only poorly described the espiw core is found off central and northern chile between the coast and 90 w and 20 38 s located at 50 400 m of depth its temperature varies between 11 13 c salinity ranges from 34 1 34 3 and its sigma t lies between 25 75 26 25 kgm 3 espiw spreads with the subtropical gyre circulation and can be traced to at least 150 w formed through the process of subduction southeastward of the wind driven gyre circulation the espiw communicates surface properties of the waters off central chile to tropical latitudes

warming and weakening of the abyssal flow through samoan passage abstractthe abyssal flow of water through the samoan passage accounts for the majority of the bottom water renewal in the north pacific thereby making it an important element of the meridional overturning circulation here the authors report recent measurements of the flow of dense waters of antarctic and north atlantic origin through the samoan passage a 15 month long moored time series of velocity and temperature of the abyssal flow was recorded between 2012 and 2013 this allows for an update of the only prior volume transport time series from the samoan passage from woce moored measurements between 1992 and 1994 while highly variable on multiple time scales the overall pattern of the abyssal flow through the samoan passage was remarkably steady the time mean northward volume transport of about 5 4 sv 1 sv 106 m3 s 1 in 2012 13 was reduced compared to 6 0 sv measured between 1992 and 1994 this volume transport reduction is significant within 68 confidence limits 0 4 sv but not at 95 conf

early diagenesis of trace metals cd cu co ni u mo and v in the freshwater reaches of a macrotidal estuary vertical profiles from the water column including the maximum turbidity zone mtz to the consolidated sediment were sampled in september 2000 in the freshwater reaches of the gironde estuary during a complete neap tide spring tide cycle the vertical distributions of dissolved major redox parameters and metals mn fe cd cu v co ni mo and u were determined reactive particulate metal fractions were also determined from selective leaching the studied system is characterized by density layers functioning at different time scales consisting of two mobile layers i e the liquid lm and the soft mud sm overlying consolidated sediments cs this results in a three zone diagenetic regime where 1 o2 dynamics are fast enough to show depletion in the rapidly mixed lm sequence tidal time scale 2 denitrification occurs on the weekly time scale mixing sm sequence and 3 the mn fe and sulfate cycling occurs in the cs layer annual time scale the studied trace metals show differential behavior during early diagenesis 1 cd cu and v are released into pore water preferentially from organic matter in the sm 2 co ni and u are released in the cs from mn and fe oxides during reductive dissolution and 3 mo from both processes transient conditions i e oscillations of redox fronts and reoxidation processes due to the dynamics of the mobile layers strongly influence the trace metal distributions as inducing resolubilization cd cu and mo in the cs authigenic metal phases accumulate either by direct precipitation with sulfides cu cd or co precipitation with fe sulfides mo microbially mediated reduction of fe oxides is proposed to control u removal from pore water by reduction of u vi to u iv at depth however a significant fraction of the trace metals is trapped in the sediment in exchangeable forms and therefore is susceptible to be mobilized due to resuspension of estuarine sediment during strong river flood periods and or dredging activities

a first transect of 236u in the north atlantic ocean abstract in this study the first comprehensive dataset of 236u in the north atlantic ocean is presented 236u 238u ratios and 236u concentrations are determined in about 70 seawater samples collected from 9 depth profiles along a transect through the northwest atlantic ocean during the first two legs of the geotraces cruise ga02 in 2010 the cruise track was designed to follow the path of the north atlantic deep water nadw from its formation region to the deep parts of the western atlantic ocean basins our results show that there is a strong north to south and surface to deep ocean gradient spanning a broad range of 236u 238u from 44 15 10 12 to 1477 91 10 12 that correlates well with the distribution of water masses in this region all measured ratios are above the theoretical pre anthropogenic levels of 10 13 to 10 14 showing that the whole transect is dominated by anthropogenic 236u based on the calculated 236u inventories the 236u inputs of global fallout and direct releases from nuclear reprocessing plants could be constrained to a range from 1000 to 1400 kg and from 115 to 250 kg of 236u from the two sources respectively our results show that the 236u 238u atomic ratio can be used as a marker of north atlantic water masses with high ratios 1000 10 12 characterizing northern water masses lsw and dsow and lowest ratios 50 400 10 12 corresponding to the increasing influence of aabw and aaiw

metal fixation and mobilisation in the sediments of the afon goch estuary dulas bay anglesey abstract the surface drainage waters of parys mountain anglesey wales a site of former mining for base metals are highly acidic and metal rich due to the oxidation of sulphide minerals these acid waters mix with more neutral waters in the afon goch downstream of parys mountain allowing the formation of ochre precipitates which are found throughout the length of the afon goch and dulas bay x ray fluorescence xrf analysis of the ochres that settle where the afon goch enters dulas bay fe 2 o 3 18 wt reveals that they are heavily contaminated with cu 13 000 g g and zn 7700 g g these sediments are black immediately below the surface and porewater analysis confirms that sulphate reduction is taking place samples of both stream ochre and anoxic black mud have been analysed by exafs spectroscopy data from the exafs analysis of the ochre sample reveals that the fe cu and zn are bonded to oxygen in poorly ordered or amorphous solids in the anoxic black mud however fe cu and zn are all present as sulphides the fe sulphide is either amorphous or poorly ordered whereas zn forms a discrete sulphide phase similar to sphalerite the cu sulphide has short range order with a chalcopyrite like structure sequential extraction analysis of the same samples was also performed for the ochre sample cu and zn release is controlled by the fe hydrated oxides being recovered primarily in the mildly acid carbonate and more strongly acid and reducing reducible fractions fe and zn are also recovered in these fractions from the black mud indicating that these metals are present as acid soluble sulphides cu however is almost exclusively recovered in the oxidisable fraction indicating that it is incorporated into a more stable sulphide such as chalcopyrite

trace metal deposition and mobility in the sediments of two lakes near sudbury ontario the accumulation and mobility of fe mn al cu ni and pb in the sediments of two lakes clearwater ph 4 5 and mcfarlane ph 7 5 near sudbury ontario have been investigated the al cu and ni concentrations are expectedly relatively high in the overlying waters of clearwater lake and much lower for al and cu in mcfarlane lake the low trace metal concentrations found in the anoxic porewaters of clearwater lake could be explained by a sharp increase in porewater ph concomitant with so42 reduction and h2s production within the first 1 2 cm of the sediments which has conceivably led to the precipitation of mineral phases such as al oh 3 nis and cus in both lakes fe concentrations in anoxic porewaters appear to be controlled by fes and or feco3 formation solubility calculations also indicate mnco3 precipitation in mcfarlane lake in clearwater lake however both porewater and total mn were relatively low a possible result of the continuous loss of mn ii through the acidic interface it is suggested that upwardly decreasing total mn profiles resulting from the removal of mn from the top sediment layers under acidic conditions may constitute a reliable symptom of recent lake acidification the downward diffusion of ai cu and ni from the overlying water to the sediments has been estimated from their concentration gradients at the interface and compared to their total accumulation rates in the sediments in both lakes the diffusion of al is negligible compared to its accumulation rate however diffusion accounts for 24 52 of the accumulation of cu in the sediments of clearwater lake but appears negligible in mcfarlane lake the downward diffusive flux of ni is important and may explain 76 161 of the estimated ni accumulation rate in clearwater lake and 59 in mcfarlane lake the porewater cu and ni profiles suggest that the subsurface sedimentary trace metal peaks observed in clearwater lake as in other acid lakes may not be caused by sediment leaching or by a recent reduction in sedimentation but may have a diagenetic origin instead diffusion to the sediments thus appears to be an important and previously overlooked trace metal deposition mechanism particularly in acid lakes

a depth profile of uranium 236 in the atlantic ocean abstract in this study the first two oceanic depth profiles of 236u sampled in the western equatorial atlantic ocean are presented the measured 236u 238u ratios decrease from about 10 9 at the surface down to about 10 10 even the lowest ratios measured below 4000 m depth are more than three orders of magnitude above the estimated natural 236u 238u level for the pre anthropogenic ocean this clearly indicates that anthropogenic 236u already has reached the deep atlantic ocean three different conceptual models are applied to identify the relevant processes capable of transporting significant amounts of 236u from the surface into the deep ocean while the vertical transport of particulate u is excluded as a significant source box model calculations suggest that north atlantic deep water production with some minor contribution of 236u from nuclear reprocessing as the most likely source for 236u in the deep western equatorial atlantic ocean our results show that 236u has a large potential as a new conservative and transient tracer in oceanography

arsenic distributions in porewaters and sediments of puget sound lake washington the washington coast and saanich inlet b c solid phase as mn al and excess 210pb and dissolved total as as 3 as 5 mn 2 fe 2 po 34 nh 4 and h2s profiles in 12 cores from puget sound lake washington the washington coast and saanich inlet b c are presented typically strong correlations between solid phase as and mn concentration maxima in surficial sediments are a result of intense as scavenging in the overlying waters by mn or ferich phases or solid phase as dissolution at depth followed by upward diffusion and co precipitation with mn or fe oxides at or near the sediment water interface atypically anthropogenic inputs cause high sedimentary as concentrations without accompanying high mn levels sedimentary as fluxes are an order of magnitude greater in puget sound and lake washington than off the washington coast and in saanich inlet porewater total as concentration profiles exhibit sub surface maxima with magnitudes 10 60 times greater than in overlying bottom waters porewater maxima in marine environments are proportional to associated solid phase as concentrations these maxima consistently occur within 1 0 cm of the bottom of the 210pb derived surface mixed layer suggesting solid phase as release to porewater in response to a redox gradient across this mixing boundary dissolved as behavior beneath these maxima indicates as removal to solid phases in marine but not lacustrine porewaters porewater as 3as 5 ratios are 1 0 for washington coastal environments and usually between 1 0 4 0 for puget sound and lake washington as 5 is below the detection limit in porewaters of saanich inlet when the overlying bottom water is anoxic but as 3as 5 ratios as low as 2 8 exist in near surface porewater under oxic bottom water conditions

diachronous exhumation of hp lt metamorphic rocks from south western alps evidence from fission track analysis new fission track ages on zircon and apatite zft and aft from the southwestern alpine paleo accretionary wedge document a contrasting cooling history from east to west in the eclogitic monviso ophiolites the zft ages are 19 6 0 8 ma and the aft ages are 8 6 1 7 ma in the ht blueschist eastern queyras zft ages range from 27 0 1 5 ma to 21 7 1 6 ma and aft ages from 14 2 2 0 to 9 4 1 1 ma in the lt blueschist western queyras zft ages are between 94 7 3 1 ma and 63 1 2 9 ma and aft ages are between 22 2 1 6 and 22 6 1 5 ma the chenaillet ophiolite yields ages of 118 1 3 7 ma on zft and of 67 9 8 5 ma on aft these new ft data combined with petrological and geochronological constraints record a diachronous exhumation in the paleo accretionary wedge during subduction and collision

water masses in the humboldt current system properties distribution and the nitrate deficit as a chemical water mass tracer for equatorial subsurface water off chile abstract three sections are used to analyze the physical and chemical characteristics of the water masses in the eastern south pacific and their distributions oceanographic data were taken from the scorpio may june 1967 piquero may june 1969 and krill june 1974 cruises vertical sections of temperature salinity dissolved oxygen nitrate nitrite phosphate and silicate were used to analyze the water column structure five water masses were identified in the zone through t s diagrams subantarctic water subtropical water equatorial subsurface water antarctic intermediate water and pacific deep water their proportions in the sea water mixture are calculated using the mixing triangle method vertical sections were used to describe the geographical distributions of the water mass cores in the upper 1500 m several characteristic oceanographic features in the study area were analyzed the shallow salinity minimum displacement towards the equator the equatorial subsurface salinity maximum associated with a dissolved oxygen minimum zone and a high nutrient content displacement towards the south and the equatorward intermediate antarctic salinity minimum associated with a dissolved oxygen maximum the nitrate deficit generated in the denitrification area off peru and northern chile is proposed as a conservative chemical tracer for the equatorial subsurface waters off the coast of chile south of 25 s

metal distribution during diagenesis in the contaminated sediments of dulas bay anglesey n wales uk the tessier sequential extraction procedure was applied to discrete layers from 9 sediment cores from dulas bay anglesey results provide data on the chemical association of heavy metals fe mn cu zn cd and as with major sedimentary phases and provide information on changes in metal partitioning associated with the changing physicochemical conditions encountered during burial extremely high concentrations of heavy metals were recorded e g zn 3000 g g 1 cu 2000 g g 1 and resulting depth profiles clearly indicate the differential behaviour of metals during diagenesis where with increasing depth fe mn and cu become increasingly associated with sulphide phases substantial changes in porewater concentrations indicate zones of preferential mobilisation due to sharp alterations in physicochemical conditions all metals are involved in processes of post depositional diagenetic cycling driven by organic matter degradation and o2 utilisation in thermodynamically favoured sequence fe and mn oxide and oxyhydroxide dissolutionact as controlling variables leading to zones of solid phase metal enrichment phase equilibria have been calculated to elucidate observed solid phase partitioning at the redox boundary and processes of subsurface sulphide mineral formation

iron geochemistry in surface sediments of a temperate semi enclosed bay north china iron fe speciation and microbial reducible fe iii oxides mr fe iii in surface sediments of semi enclosed jiaozhou bay were quantified to reveal fe geochemistry in the settings subjected to anthropogenic perturbations results indicate that sedimentary fe in the bay is mainly of natural weathering source without appreciable anthropogenic fe inputs as indicated by a generally good linear coupling of total fe to aluminum among the three highly reactive fe iii fe iii hr pools well crystalline fe iii oxides fe iii wc were always the predominant phase followed by poorly crystalline fe iii oxides fe iii pc and amorphous fe iii oxides fe iii am were only of minor importance the dominance of non sulfidized fe ii over sulfidized fe in the sediments points to the importance of microbial iron iii reduction mir in the free sulfide starved conditions high riverine inputs of toc leads to outliers in the fe iii hr versus total organic carbon toc ratio compared the rest of the bay om dependent mir as the common driving force has rendered all fe ii bearing phases linearly coupled to toc mr fe iii in the surface sediments covered all fe iii am and a fraction of less reactive fe iii phases while fe iii wc was at most a minor contributor highly reactive fe appears to be enriched to some extent in the temperate semi enclosed bay as in the wet tropical counterparts

control of early diagenesis processes on trace metal cu zn cd pb and u and metalloid as sb behaviors in mining and smelting impacted lacustrine environments of the bolivian altiplano abstract a combination of mineralogical sem eds empa and geochemical redox dynamics selective extractions approaches was applied to mining and smelting impacted sediments from lake uru uru and from the cala cala lagoon a non impacted reference site in the bolivian altiplano the purpose was to assess the factors controlling the post depositional redistribution mobilization sequestration of trace metals and metalloids as expected trace metals and metalloids are less reactive at the reference site than in lake uru uru in the latter trace metals and metalloids are principally hosted by fe and mn oxyhydroxides authigenic sulfides and silicate particulates post depositional redistribution is ascribed to early diagenetic processes driven by organic matter om mineralization including dissolution of trace metal bearing phases and precipitation of authigenic sulfide and carbonate phases seasonal climate variability exerts a strong influence on these processes evaporation of surface water during the dry season in the northern part of lake uru uru promotes large redox front oscillations in the sediments and therefore transient redox conditions likely leading to the weakening of anoxia in near surface sediments and to a compressed redox zonation compared to the southern part of the lake seasonal disappearance of the water column in the northern lake uru uru entails an alternation of i low trace element mobility in the dry season due to elemental precipitation and ii an increase of trace element mobility via diffusive transport during the wet season due to release from om fe and mn oxyhydroxides and carbonates upon mineralization reductive dissolution and destabilization processes respectively reoxidation of authigenic fe sulfides likely following the re instalment of the water column above the sediment at the end of the dry season and prior to the return of anoxia probably favors transport of trace elements to the water column as a consequence of this intricate web of redox and climate related processes both northern and southern sediments of lake uru uru are a source of dissolved trace elements particularly as and cd for the overlying water column via diffusive transport however much of the diffused as and cd is likely to be removed from the dissolved phase by the redox loop through fe oxyhydroxide precipitation finally it is suggested that long term sequestration of trace metals and metalloids in the sediments could be controlled by inter annual climate variability such as enso events

natural enrichment of arsenic in loch lomond sediments abstract concentrations of arsenic in surface or near surface sediment in 12 of 13 cores from the three major basins of loch lomond are substantially enhanced up to 675 mg kg compared with background values of 15 50 mg kg sedimentary as profiles are attributed to post depositional enrichment processes since there are no recent significant sources of environmental as contamination anthropogenic or natural in the loch lomond area the enrichments can be interpreted in terms of post depositional diagenetic remobilization processes in sediment reducing zones followed by upward migration of as through interstitial waters and oxidation adsorption precipitation reactions in near surface oxidizing layers confirmation of the diagenetic adsorption hypothesis is provided directly by the analysis of as species 1 5 81 g l in pore water and indirectly via comparison with sedimentary phosphorus

thermobarometric data from a fossil zircon partial annealing zone in high pressure low temperature rocks of eastern and central crete greece abstract a fossil partial annealing zone of fission tracks in zircon is described from high pressure low temperature hp lt rocks of the phyllite quartzite unit pq on the island of crete greece correlation of regional trends in fission track age populations with independent thermobarometric and microstructural data and with new experimental annealing results allows a calibration of this low temperature thermochronological method to a degree hitherto not available from other field examples the zircon fission track ft ages of samples from the pq across crete range from original detrital signature through reduced to completely reset the annealing is the result of a single heating period related to the hp lt metamorphism with near peak temperatures lasting for only a few million years some time between 24 1 and 20 1 ma in eastern crete where rocks have experienced temperatures of 300 50 c and pressures of 0 8 0 3 gpa zircon ft ages range from 414 24 to 145 10 ma ages above 300 ma occur mostly near the east coast of the island in rocks which have not been heated to above ca 280 c and probably represent a pre variscan source track lengths are already indicative of a substantial annealing at this temperature most of the zircon ft ages from eastern crete scatter within error around the stratigraphic age samples with apparent zircon ft ages significantly younger than the depositional age are only observed in areas where temperatures exceeded ca 320 c towards the west a sudden decrease to very young ages ranging from 17 2 to 18 1 ma reflects a complete resetting at ca 350 c short tracks however are still observed throughout the central and western part of the island ages are consistently below 22 ma thermobarometric data for this area indicate maximum temperatures of 400 50 c and pressures of 1 0 3 gpa only samples from western crete which have been exposed to 400 50 c show exclusively long tracks consequently the high temperature limit of the zircon partial annealing zone zpaz appears to be between 350 and 400 c a significant influence of elevated confining pressure on the stability of fission tracks in zircon is ruled out by the results of annealing experiments at 0 5 gpa and at different temperatures which fit the curves previously obtained by other authors at ambient pressure

the importance of serpentinite mylonites for subduction and exhumation of oceanic crust abstract in the ultramafic erro tobbio unit voltri massif western alps a set of overprinting structures in serpentinite mylonites is related to alpine subduction to about 80 km depth and to subsequent exhumation antigorite mylonites are cut by en echelon olivine veins which in turn are dissected by multiple sets of shear bands containing olivine and titanian clinohumite the transition from olivine free to olivine bearing structures indicates recrystallization during prograde metamorphism all structures display the same top to the nw kinematics providing evidence for a continuous non coaxial deformation the serpentinite mylonites surround km scale bodies of pre alpine peridotite which show only minor alpine overprint this indicates that during subduction related deformation recrystallization and fluid flow were strongly localized within serpentinite mylonites olivine bearing discontinuous shear planes with top to the se sense of movement crosscut the prograde structures the inversion of shear sense suggests a change in position of the serpentinites relative to the downgoing slab i e from the subducted slab to the upper plate during accretion thus the shear sense inversion marks the change from burial to exhumation of the serpentinites the low density of antigorite serpentinites 2 75 g cm3 causes strong buoyancy thus providing a mechanism for the exhumation of deeply subducted rocks it is suggested that serpentinites may act as carriers for the uprise of eclogite bodies which have higher densities than the peridotitic upper mantle

early tertiary eclogite facies metamorphism in the monviso ophiolite although crucial for the construction of tectonic models of the alps the timing of high pressure metamorphism is still poorly determined and controversial it is likely to vary from one tectonic unit to another depending on when each became involved in subduction this in turn relates to palaeogeographic position with respect to the active ocean basin well defined reliable geochronological data are too few to test this hypothesis this paper extends the database by determining sm nd mineral isochrons on two samples from the monviso ophiolite in the piemonte zone carefully selected to minimize the problems of sm nd dating of eclogites encountered elsewhere in the alps the dated samples have eclogite facies mineral assemblages typical of the lago superiore unit of the ophiolite mineral compositions are similar to previously reported samples and indicate pressures of around 2 gpa and temperatures of 400 500 c sm nd isochron ages of 60 12 and 62 9 ma are defined by garnet and clinopyroxene while the rb sr age on phengite which is part of the high p assemblage is 40 1 ma the new data fit an emerging pattern of ages in which high p metamorphism in the oceanic realm is early tertiary with slightly older ages in the overlying sesia zone and younger oligocene ages in the underlying internal basement massifs which only became involved in subduction when closure of the piemont ocean was complete

high resolution profiles of trace metals assessed by dgt techniques in lake sediment porewaters the technique of diffusive gradients in thin films dgt was applied to obtain high resolution vertical profiles of trace metals in sediment porewater of a eutrophic lake lake chaohu all sampling sediments were under anaerobic conditions with eh values below 0 the redox potential profile in m4 was relatively stable and higher eh values in m4 than that in m1 were observed due to hydrodynamic effects fe mn and as exhibited closely corresponding profiles due to the co release of fe and mn oxides and the reduction of as higher fe and mn concentrations and lower as concentrations were observed in m1 of the western half lake than those in m4 of the eastern half lake due to different sources and metal contamination levels in the two regions cu and zn showed increasing concentrations similar to mn and fe at 1 2 cm depth of sediments while dgt measured co ni cd and pb concentrations decreased down to 3 4 cm in the profiles co ni cu zn cd and pb showed insignificant regional concentration variances in the western and eastern half lakes according to the r c dgt c centrifugation values the rank order of metal labilities decrease as follows fe 1 cu pb zn 0 9 co ni cd 0 3 mn as 0 1

first 236u data from the arctic ocean and use of 236u 238u and 129i 236u as a new dual tracer the first dataset of 236u 238u in the water column of the arctic ocean ao is presented and shows the widest range of ratios reported so far in the open ocean from 5 55 5 to 3840 260 10 12 3840 260 10 12 surface samples and depth profiles were collected during two geotraces expeditions in 2011 2012 and analyzed for the concentrations of 236u and 129i with the aim of investigating whether the combination of 236u 238u and 129i 236u can be used as a new oceanographic tool in the ao results show that the distributions of the 236u 238u and 129i 236u atomic ratios are consistent with the different water masses in the ao high 236u 238u and 129i 236u ratios in the upper water column 2000 10 12 2000 10 12 and 200 respectively illustrate the penetration of atlantic waters aw into the ao lower values were found in pacific waters pw and deep waters of the ao rivers seem to represent a temporally and spatially constrained third anthropogenic source of 236u but more data are needed to confirm this in a simple mixing model the combination of 236u 238u and 129i 236u reveals a high contribution 99 of natural background waters pre nuclear era in the deep and bottom waters of the amerasian basin indicating an apparent water mass renewal time of 1000 years despite the relatively high apparent age of the amerasian basin deep waters this work shows the potential of using the dual tracer approach as a new oceanographic tool in the arctic ocean

from passive margin to continental collision a tectonic scenario for the western alps general transverse section just south of the pelvoux massif european margin of tethys an ancient atlantic type margin it was subject to extension from triassic to the beginning of late cretaceous times and to collision thereafter as the result of convergence of the eurasian and african continents paleogeographic evolution is outlined a new alpine tectogenetic reconstruction is proposed an attempt is made to establish how the previous extensional structures influenced the later tectonic evolution modified journal abstract

the geotraces intermediate data product 2017 the geotraces intermediate data product 2017 idp2017 is the second publicly available data product of the international geotraces programme and contains data measured and quality controlled before the end of 2016 the idp2017 includes data from the atlantic pacific arctic southern and indian oceans with about twice the data volume of the previous idp2014 for the first time the idp2017 contains data for a large suite of biogeochemical parameters as well as aerosol and rain data characterising atmospheric trace element and isotope tei sources the tei data in the idp2017 are quality controlled by careful assessment of intercalibration results and multi laboratory data comparisons at crossover stations the idp2017 consists of two parts 1 a compilation of digital data for more than 450 teis as well as standard hydrographic parameters and 2 the egeotraces electronic atlas providing an on line atlas that includes more than 590 section plots and 130 animated 3d scenes the digital data are provided in several formats including ascii excel spreadsheet netcdf and ocean data view collection users can download the full data packages or make their own custom selections with a new on line data extraction service in addition to the actual data values the idp2017 also contains data quality flags and 1 data error values where available quality flags and error values are useful for data filtering and for statistical analysis metadata about data originators analytical methods and original publications related to the data are linked in an easily accessible way the egeotraces electronic atlas is the visual representation of the idp2017 as section plots and rotating 3d scenes the basin wide 3d scenes combine data from many cruises and provide quick overviews of large scale tracer distributions these 3d scenes provide geographical and bathymetric context that is crucial for the interpretation and assessment of tracer plumes near ocean margins or along ridges the idp2017 is the result of a truly international effort involving 326 researchers from 25 countries this publication provides the critical reference for unpublished data as well as for studies that make use of a large cross section of data from the idp2017 this article is part of a special issue entitled conway geotraces edited by tim m conway tristan horner yves plancherel and aridane g gonzalez

neogene kinematics of the central and western alps evidence from fission track dating zircon and apatite fission track analysis has established the continuation of a zone of rapid change in mineral ages extending from the simplon fault zone in the simplon alps through the rhone valley and along the southeastern side of the mont blanc and belledonne massifs apatite fission track ages to the northwest of this zone generally range from 1 4 to 6 ma whereas those to the southeast range from 6 to 13 ma corresponding values for zircon are 11 13 and 16 26 ma respectively the zone corresponds to the position of the frontal pennine thrust in the mont blanc belledonne region this structure a prominent feature on recent deep seismic profiles may have been reactivated in the neogene with an important normal fault component this is suggested by apatite and zircon fission track ages in the footwall that are younger than those in the hanging wall and by the observed elimination of the lower pennine or simplon nappes along this fault zone in the rhone valley mont blanc belledonne region resulting in the juxtaposition of north penninic and helvetic ultra helvetic nappes at the current erosion level the distribution of fission track ages reflects this movement and the related neogene exhumation of the mont blanc and belledonne external massifs which has continued until less than 1 4 m y ago i e it is almost certainly still active and has tilted the overlying nappe sequence

annealing kinetics of fission tracks in zircon an experimental study a series of laboratory annealing experiments on zircon fission tracks has been carried out under heating conditions of 350 750 c for 10 1 103 hr i e 4 5 min 40 days variation in the confined lengths of spontaneous fission tracks was determined using zircon grains from nisatai dacite the fading contours of normalized mean track length r on the arrhenius diagram showed as sets of straight lines we performed a series of model fittings called the parallel and fanning models in order to describe the decrease in r with increasing temperature or heating time the lowest temperature limit of the zircon partial annealing zone zpaz was defined as r 0 95 and the highest as r 0 4 which approximately corresponded to the total fading of surface tracks extrapolation of the results of the laboratory experiments to the geological timescale gives for a heating duration of 106 yr estimated values of the zpaz of 210 320 c 60 c 2 with the parallel model 190 350 c 50 c 2 with the fanning model critical temperature t0 and 170 390 c 50 c 2 with the fanning model t0 the temperatures of the zpaz decrease by 20 c for an annealing duration that is an order of magnitude longer because the estimated closure temperature of zircon fission track analysis approximately corresponds to the middle of the zpaz these results support the previously estimated closure temperature of 240 c by varying the etching time it was revealed that significant removal of radiation damage occurs at r 0 93

radiocarbon based circulation age of the world oceans 1 the distributions of deep ocean 14c data are often used to illustrate the rate of deep ocean circulation the associated conventional 14c ages show a difference of 1000 years between the north atlantic and the southern ocean and a difference of another 1000 years between the southern ocean and the north pacific these differences may be interpreted directly and mistakenly as the timescale of circulation the characterization of the deep ocean circulation being millennial is common using objectively gridded natural 14c data of key et al 2004 i recast 14c in terms of circulation by accounting for 1 long surface ocean reservoir 14c ages and 2 two sources of deep water formed in the north atlantic and around antarctica the new distribution of circulation 14c ages is more consistent with the deep ocean being characterized by a centennial timescale than a millennial timescale also the role of the southern sourced deep water is now made more obvious by accounting for the two important controls on oceanic 14c that are not well known outside the field of chemical oceanography the new map will be useful as an illustration of global deep ocean circulation to the wider scientific community and as a pedagogical tool to new students in earth sciences and oceanography

diagenetic processes on metals in hypersaline mudflat sediments from a subtropical saltmarsh se gulf of california postdepositional mobility and geochemical fractions abstract to understand the biogeochemical cycles of trace metals cd cu fe mn ni and zn in a hypersaline subtropical marsh geochemical studies of both interstitial and solid phases were conducted on sediment cores from chiricahueto marsh se gulf of california the sequential extraction procedure proposed by tessier was used to estimate the percentages of the metals present in each geochemical phase of the sediment metal concentrations in the solid phase were found to be enriched in the upper layers and mainly associated with reactive fractions such as organic matter fe mn oxyhydroxides and carbonates 46 74 of ni mn and cd and 11 19 of cu and zn principal factor analysis pfa and spearman correlation analysis revealed a strong positive association of metals and their reactive phases with oc the diagenetic component and a negative or non association with the mud content al fe and li the lithogenic component diagenetically released metals are mainly mobilized within hypersaline sediments by buoyancy transport 90 of total flux in response to an extreme salinity gradient by input of fresh groundwater 3 6 psu cm 1 the molecular diffusion due to the gradient of metals in porewater maximum and higher levels at 5 7 and below 20 cm depth respectively is significantly less important to the advective transport most of the metals mobilized by diffusion advection processes are re precipitated in the sediments by authigenic minerals only

fission track evidence for late triassic oceanic crust in the french occidental alps five zircons and one apatite from plutonic rocks of the ophiolitic sequence from the piemontese zone western alps southeast france have been dated by the fission track method the ages obtained indicate that the minimum age of the alpine oceanic crust in this zone is between 192 6 and 212 8 m y late triassic liassic consideration of the available data on fission track retention conditions in zircons and pressure temperature conditions allowed by the high pressure mineralogic assemblages of the rocks leads to the conclusion that in the external part of the piemontese zone the temperature duration conditions of the high pressure alpine metamorphism were inadequate to significantly reset the zircons9 fission track clock suggesting a short lived metamorphic event

miocene to present differential exhumation in the western alps insights from fission track thermochronology 1 analysis of cooling age patterns yielded by low temperature thermochronometers provides key information about the role played by tectonic discontinuities during the late stages of exhumation of metamorphic belts in the western alps fission track data published so far are heterogeneously scattered and concentrated in few structural domains preventing analyses at the scale of the whole belt the new apatite fission track data reported in this work obtained with the external detector method as well as the population method in very low u content samples fill this gap they constrain the postmetamorphic evolution of the western alps along two transects from the foreland to the retroforeland unraveling the effective role played by some major faults during the exhumation of the belt at shallow crustal levels a clear regional pattern characterized by decreasing ages moving from the axial sector to the european external sector of the belt and by an along strike gradient with increasing ages from north to south has been unraveled evident breaks in this age pattern have been detected in correspondence of faults that are near parallel to the trend of the belt pointing to the occurrence of active tectonics during and after exhumation the most apparent breaks have been observed in the axial sector of the belt where the postmetamorphic deformation would have been negligible according to classic tectonic models faults located in the axial sector split the belt into two major blocks eastern and western since the miocene the western block experienced higher exhumation rates than the eastern one such differential exhumation was accommodated in the northern portion of the belt thanks to reverse motion along the internal houiller fault which occurred in a convergent transcurrent framework to the south it was accommodated instead by normal reactivation of the brianconnais front and by activity of the longitudinal fault system which occurred in a divergent transcurrent framework the tectonic activity affecting the axial sector of the belt in a context of regional dextral strike slip is coeval with the forward propagation of the external thrusts and of similar magnitude we suggest that the contrasting kinematic regimes i e convergent versus divergent transcurrence observed in the western alps moving along strike were responsible of the increasing exhumation rates toward the north revealed in both blocks by the along strike age gradient the higher exhumation rates recognized northward would be related to an increasing importance of crustal shortening that promoted erosion during the late stages of exhumation of the belt

distribution of 236u in the u s geotraces eastern pacific zonal transect and its use as a water mass tracer abstract we report dissolved concentrations of the long lived radioisotope 236u measured in the water column along the 2013 us geotraces eastern pacific zonal transect gp16 this transect followed a 10 15 s line from manta ecuador to papeete haiti french polynesia crossing the southern east pacific rise intercepting one of the largest hydrothermal plumes as well as a productivity gradient which includes the upwelling zone and associated low oxygen waters offshore from peru and the oligotrophic sub tropical gyre accelerator mass spectrometry was used to measure dissolved seawater 236u concentrations as low as 1 103 atom kg 1 which are among the lowest levels reported to date differences in upper water column 236u distributions from east to west are a result of variable contributions from different surface and intermediate waters encountered along the transect the distribution of 236u both in depth and geographically provides complementary information to that obtained from 14c and helium isotopes demonstrating that 236u concentrations are diagnostic in the identification of and contributions from the different deep and bottom water masses encountered along the epzt jenkins et al 2017 for example we observe minimum 236u concentrations along the epzt between 2000 and 3000 m that are consistent with contributions attributed to pacific deep water we also observe increases in 236u below 3000 m at the eastern and western termini of the epzt this is consistent with contributions associated with antarctic bottom water and lower circumpolar deep water our results indicate that 236u may be used in conjunction with 14c and 3he isotopes as an additional tool with which to identify and resolve contributions from different water masses in the pacific ocean this article is part of a special issue entitled cycles of trace elements and isotopes in the ocean geotraces and beyond edited by tim m conway tristan horner yves plancherel and aridane g gonzalez

speciation and spatial distribution of solid phase iron in surface sediments of the east china sea continental shelf abstract speciation and reactivity characterization of solid phase fe in marine sediments are of significance to understanding its heterogeneous mineralogy and crystallinity the diagenetic cycling of fe and its regulating roles on many other elements in sediments in this study a combination of sequential and single step extractions was used for the determination of seven fe pools in surface sediments of the east china sea ecs continental shelf 1 carbonate associated fe fe ii carb plus acid volatile sulfide fe fe ii avs 2 easily reducible amorphous poorly crystalline fe oxides fe ox1 3 reducible crystalline fe oxides fe ox2 4 magnetite fe mag 5 poorly reactive sheet silicate fe fe prs 6 pyrite fe fe py and 7 unreactive silicate fe fe u total fe fe t in the sediments is largely determined by terrestrial aluminosilicate particles as indicated by a great similarity of the fe t with that of the yangtze river and global riverine particulates the size of fe prs is found to be the largest pool followed by fe u fe ox2 fe mag fe ii avs carb fe ox1 and fe py the large fe prs may result from neoformation of fe rich clay minerals via reverse weathering and subsequent ageing the small sizes of fe ii avs carb and fe py pools is believed to be the result of low so 4 reduction due to generally low labile organic matter together with the oxic suboxic dynamic environments of the surface sediments the occurrence of fe ox1 fe ox2 and fe prs in the sediments is closely associated with the clay fraction as indicated by a high spatial correlation between the former and the latter highly reactive fe fe hr in the sediments is comparable to that in global marine sediments but apparently lower than in the yangtze river and global riverine particulates due probably to sequestration in the yangtze estuary the ratios of fe hr fe t fe pr fe t and fe u fe t in the ecs surface sediments consistently show more similarity to those in the yangtze river particulates than in the global continental margin or deep sea sediments the surface sediments maintain a high level of buffering capacity toward sulfidation suggested by a large fraction of highly reactive fe iii oxides fe iii hr in fe hr

pb sr nd isotopic behavior of deeply subducted crustal rocks from the dora maira massif western alps italy ii what is the age of the ultrahigh pressure metamorphism pb nd and sr isotope data are reported from two localities on mineral separates from mg rich metapelites and associated rocks that have been subducted to depths of at least 100 km for which metamorphic conditions are estimated at 28 33 kilobars pressure and 700 800 c and then returned to the surface initial isotope ratio data from the granitoid country rock are similar to those found in the metapelites the initial ratios indicate predominantly recycled aged granitic crustal materials for the sources of all of the samples five zircon samples 4 from pyrope megacrysts and 1 from fine grained pyrope quartzite lenses in the metapelites accurately define a chord yielding intercept ages of 304 10 and 38 0 1 4 ma in a concordia diagram zircon from the country rock also plots along the chord the zircon data together with initial nd and sr data indicate that the sedimentary sources of the rocks were derived mainly or entirely from sialic hercynian rocks ellenbergerite from pyrope megacrysts and monazite from the fine grained ground mass yield slightly younger ages of 30 34 ma apparently reflecting lower blocking temperatures than that of zircon sm nd data from a pyrope megacryst give an errorchron corresponding to an age of 38 ma in agreement with the zircon date a major question concerns the timing of the ultrahigh pressure metamorphism experimental data suggest that pyrope and quartz coesite as well as ellenbergerite formed by various metamorphic reactions if as generally assumed the ultrahigh pressure metamorphism occurred ca 100 ma ago our data require that the zircon did not experience measurable lead loss at that time but lost major amounts of lead 38 ma ago during late alpine metamorphism estimates of diffusion rates for nd in pyrope further suggest that the apparent sm nd age of 38 ma for the megacryst is not consistent with that model those problems are resolved if the ultrahigh pressure metamorphism occurred 38 40 ma ago but problems remain from ar ar dates of 100 ma on phengite an inferred 120 ma age for zircon lead loss from another study and possibly by the very rapid uplift required if the metamorphism is that young

reconstruction of the 236u input function for the northeast atlantic ocean implications for 129i 236u and 236u 238u based tracer ages a reconstruction of historical discharges of 236u into the northeast atlantic ocean by nuclear installations is presented the nuclear reprocessing facilities sellafield sf great britain gb and la hague lh france and potentially also the nuclear fuel processing installation springfields sp gb represent the main contributors of 236u in the northeast atlantic ocean because data on 236u releases is lacking 236u discharges from sp and sf are estimated based on the u isotopic systematics found in the discharges from lh the resulting reconstruction of 236u releases indicates that until 2013 a total of 95 32 kg of 236u was discharged from sf sp and lh in a second step the reconstructed 236u releases are combined with 129i data from literature and oceanic and atmospheric box models are used to derive the 129i 236u and 236u 238u input functions that for example can be used to calculate tracer ages of atlantic waters in the arctic ocean our conceptual results show that the combination of 129i 236u and 236u 238u generally allows the estimation of tracer ages over the past approximately 25 yr if contributions of 236u from global fallout are considered finally as a proof of concept the new method is applied to calculate tracer ages of arctic ocean surface samples collected in 2011 12 and the results are in good agreement with literature data we conclude that the combination of 129i 236u with 236u 238u in a dual tracer approach provides a sensitive tool for the calculation of tracer ages and ventilation rates in the north atlantic region this article is protected by copyright all rights reserved