contrasting provenance and timing of metamorphism from paragneisses of the aracuai ribeira orogenic system brazil hints for western gondwana assembly abstract the aracuai orogen and the ribeira belt make up a complex neoproterozoic cambrian orogenic system the aracuai ribeira orogenic system aros located from the eastern to southeastern brazil along the aros the ediacaran rio doce magmatic arc represents a geotectonic connection between the aracuai and the ribeira orogenic domains although the nature and evolution of the rio doce plutonic rocks is regionally well established it lacks detailed studies on the paragneisses found along the western and central regions of this magmatic arc besides information on the nature and provenance of their sedimentary protoliths the paragneisses provide data to unravel the palaeogeographic scenario from the precursor to arc related basins six samples of al rich gneisses covering a large aros region were selected for electron microprobe emp mineral analyses in order to obtain geothermobarometric data and monazite ages as well as for laser ablation inductively coupled plasma mass spectrometry la icp ms isotopic analyses on zircon u pb lu hf and monazite u pb the different age spectra from detrital zircon grains and contrasting hf isotopic signatures suggest a complex sedimentary history located in the western sector of the study region the samples rc 02 and rc 34 with an 80 age peak of detrital zircon grains from 2158 ma to 1830 ma e hf t from 2 2 to 22 7 and hf t dm model ages from 3530 ma to 2440 ma suggest sediment sources located in the sao francisco craton basement the samples rc 03 also from the western sector and rc 46 from the southern sector have a more complex assemblage of detrital zircon grains with an 87 age peak from 987 ma to 592 ma e hf t from 14 9 to 2 9 and hf t dm model ages from 2220 ma to 720 ma indicating provenance from mainly juvenile sources of distinct ages candidates to be juvenile sources for rc 03 and rc 46 sedimentary protoliths are the rhyacian juiz de fora and pocrane complexes in the basement of the rio doce arc the neoproterozoic rio negro arc system of the ribeira belt and aros ophiolite complexes samples rc 30 and rc 38 from the eastern sector of the study region with most detrital zircon ages between 650 ma and 552 ma and very negative e hf t 25 3 to 16 5 suggest main sediment sources in the rio doce arc by extending u pb analyses on metamorphic zircon and monazite we have identified a complex timing of metamorphism represented by metamorphic ages ranging from 621 ma to 480 ma with the main collisional activity between 580 ma and 540 ma geothermobarometric studies on garnet porphyroblasts syn kinematic to the d 2 regional foliation show a retrograde metamorphic path typical of continental collision belts starting with p t conditions of t max 733 c and p max 6 43 kbar our data also suggest i the studied paragneisses represent distinct neoproterozoic basin stages shifting from passive to active margin settings ii if the rio negro arc system really provided sediments for the basin stage represented by the rc 03 and rc 46 paragneisses it would have amalgamated with the aros before 614 ma iii the final amalgamation of western gondwana took place around 540 ma in the focused region iv an important re heating period 520 480 ma can be related to the aros gravitational collapse after western gondwana assembly

distribution of anthropogenic co2 in the pacific ocean 1 this work presents an estimate of anthropogenic co2 in the pacific ocean based on measurements from the woce jgofs oaces global co2 survey these estimates used a modified version of the c technique modifications include a revised preformed alkalinity term a correction for denitrification and an evaluation of the disequilibrium terms using an optimum multiparameter analysis the total anthropogenic co2 inventory over an area from 120 e to 70 w and 70 s to 65 n excluding the south china sea the yellow sea the japan east sea and the sea of okhotsk was 44 5 5 pg c in 1994 approximately 28 pg c was located in the southern hemisphere and 16 5 pg c was located north of the equator the deepest penetration of anthropogenic co2 is found at about 50 s the shallowest penetration is found just north of the equator very shallow anthropogenic co2 penetration is also generally observed in the high latitude southern ocean one exception to this is found in the far southwestern pacific where there is evidence of anthropogenic co2 in the northward moving bottom waters in the north pacific a strong zonal gradient is observed in the anthropogenic co2 penetration depth with the deepest penetration in the western pacific the pacific has the largest total inventory in all of the southern latitudes despite the fact that it generally has the lowest average inventory when normalized to a unit area the lack of deep and bottom water formation in the north pacific means that the north pacific inventories are smaller than the north atlantic

neritic and pelagic carbonate sedimentation in the marine environment ignorance is not bliss synthesis of available data allows us to define general patterns of late quaternary carbonate production and sedimentation in the global ocean during high stands of sea level the neritic and pelagic environments appear to sequester approximately similar amounts of carbonate whereas during low stands of sea level the decreased neritic zone produces and accumulates approximately an order of magnitude less carbonate assuming that global accumulation of deep sea carbonates remains more or less constant during glacially induced changes in sea level the ocean becomes depleted with respect to calcium carbonate during high stands and recharges during low stands before we can achieve a better understanding of the global carbonate system however we need a better understanding of key environments and processes a production and accumulation on continental shelves both as potential sinks accumulation and as sources export to the deep sea b a better measure of pelagic carbonate production and c late quaternary late pleistocene and holocene mass accumulation rates in the deep sea

global marine gravity from retracked geosat and ers 1 altimetry ridge segmentation versus spreading rate 1 three approaches are used to reduce the error in the satellite derived marine gravity anomalies first we have retracked the raw waveforms from the ers 1 and geosat gm missions resulting in improvements in range precision of 40 and 27 respectively second we have used the recently published egm2008 global gravity model as a reference field to provide a seamless gravity transition from land to ocean third we have used a biharmonic spline interpolation method to construct residual vertical deflection grids comparisons between shipboard gravity and the global gravity grid show errors ranging from 2 0 mgal in the gulf of mexico to 4 0 mgal in areas with rugged seafloor topography the largest errors of up to 20 mgal occur on the crests of narrow large seamounts the global spreading ridges are well resolved and show variations in ridge axis morphology and segmentation with spreading rate for rates less than about 60 mm a the typical ridge segment is 50 80 km long while it increases dramatically at higher rates 100 1000 km this transition spreading rate of 60 mm a also marks the transition from axial valley to axial high we speculate that a single mechanism controls both transitions candidates include both lithospheric and asthenospheric processes

seasonal variations in the aragonite saturation state in the upper open ocean waters of the north pacific ocean seasonal variability of the aragonite saturation state ar in the upper 50 m and 100 m depths north pacific ocean npo was investigated using multiple linear regression mlr the mlr algorithm derived from a high quality carbon data set accurately predicted the ar of evaluation data sets three time series stations and p02 section with acceptable uncertainty 0 1 ar the algorithm was combined with seasonal climatology data and the estimated ar varied in the range of 0 4 0 6 in the midlatitude western npo with the largest variation found for the tropical eastern npo these marked variations were largely controlled by seasonal changes in vertical mixing and thermocline depth both of which determine the degree of entrainment of co2 rich corrosive waters from deeper depths our mlr based subsurface ar climatology is complementary to surface climatology based on pco2 measurements

new time constraints on dyke swarms related to the parana etendeka magmatic province and subsequent south atlantic opening southeastern brazil abstract 40 ar 39 ar incremental heating analyses were carried out on tholeiitic dyke swarms of santa catalina florianopolis and rio de janeiro and alkaline dykes from the proximity of rio de janeiro city southeastern brazil most of the plagioclases from the tholeiitic dykes display disturbed age spectra with younger apparent ages most often clearly correlated with alteration phases however a calculated weighted mean age from the less disturbed released fractions of the ne oriented santa catarina dyke swarm gives an age of 129 4 0 3 ma which is contemporaneous with the ponta grossa dyke swarm pgds and at least the northern parana continental flood basalts cfb the rio de janeiro tholeiitic dykes display age spectra affected by alteration and probably excess argon but with low temperature mini plateau ages between 130 6 and 129 8 ma which are concordant with previous data obtained on the pgds and rio de janeiro dyke swarms by renne et al 1996a and turner et al 1994 these new geochronological data when added to the previous ones show that the initiation of gondwana s breakup in the region was characterized by a volcano tectonic system with a geometry more complicated than the rift rift rift system suggested by many authors the different rift arms of this structural feature were operating during a brief time period mainly from 131 5 to 129 ma and were contemporaneous at least with the northern part of the parana etendeka province pep single grain and bulk sample biotite from the alkaline mainly coast parallel dyke swarm near rio de janeiro city display plateau ages around 80 ma 81 8 1 8 and 78 8 2 8 ma and 70 ma 72 5 0 5 and 69 7 0 2 ma these magmatic intrusions refer to late cretaceous flexuring and vertical movements and rift basin formations almeida 1976 due the northward progressing rifting motions separating south america and africa during south atlantic ocean formation

in situ calcium carbonate dissolution in the pacific ocean over the past several years researchers have been working to synthesize the woce jgofs global co2 survey data to better understand carbon cycling processes in the oceans the pacific ocean data set has over 35 000 sample locations with at least two carbon parameters oxygen nutrients cfc tracers and hydrographic parameters in this paper we estimate the in situ caco3 dissolution rates in the pacific ocean water column calcium carbonate dissolution rates ranging from 0 01 1 1 mmol kg1 yr1 are observed in intermediate and deepwater beginning near the aragonite saturation horizon in the north pacific intermediate water between 400 and 800 m caco3 dissolution rates are more than 7 times faster than observed in middle and deep water depths average 0 051 mmol kg1 yr1 the total amount of caco3 that is dissolved within the pacific is determined by integrating excess alkalinity throughout the water column the total inventory of caco3 added by particle dissolution in the pacific ocean north of 40s is 157 pg c this amounts to an average dissolution rate of approximately 0 31 pg c yr1 this estimate is approximately 74 of the export production of caco3 estimated for the pacific ocean these estimates should be considered tomore be upper limits for in situ carbonate dissolution in the pacific ocean since a portion of the alkalinity increase results from inputs from sediments less

width of continental rifts and rheological layering of the lithosphere abstract a review of some well known continental rifts shows that rift features such as maximum basin depth are dependent on the amount of extension conversely the initial rift width appears to be independent of the amount of extension a comparison is made with laboratory models of rifts developed in a brittle ductile lithosphere experimental models show that normal faults which bound a graben initially meet at the brittle ductile interface a relation between initial rift width and the depth of the brittle ductile transition is thus suggested implications for natural examples are discussed

carbon dynamics and community production in the mississippi river plume dissolved inorganic carbon dic total alkalinity talk ph and dissolved oxygen do were determined in the mississippi river plume during five cruises conducted in the spring summer and fall in contrast to many other large rivers both dic and talk were higher in river water than in seawater substantial losses of dic relative to talk occurred within the plume particularly at intermediate salinities dic removal was accompanied by high do high ph and nutrient depletion and was attributed to high phytoplankton production as a result the carbonate saturation in the plume became much higher than in ocean and river waters a mixing model was used to determine dic removal we provide evidence that the use of a two end member river and ocean mixing model was valid during late summer and fall low discharge period however for other periods we used salinity and talk to delineate a mixing model that included two river end members and an ocean end member net community production rates in the plume estimated using a box model peaked in the summer and were among the highest reported to date for large river plumes in the summer and fall biological production in the river plume consumed a majority of the available nutrients whereas during the spring only a small fraction of the available nutrients were consumed in the plume biological production was the dominant process influencing ph and carbonate saturation state along the river ocean gradient whereas physicochemical dynamics of mixing played an important role in controlling the talk and dic distributions of this large river plume

coupling primary production and terrestrial runoff to ocean acidification and carbonate mineral suppression in the eastern bering sea water column ph and carbonate mineral saturation states were calculated from dissolved inorganic carbon dic and total alkalinity data collected over the eastern bering sea shelf in the spring and summer of 2008 the saturation states of the two most important carbonate minerals calcite calcite and aragonite aragonite were strongly coupled to terrestrial runoff from the yukon and kuskokwim rivers primary production in the surface waters and remineralization of organic matter at depth over the shelf in spring before ice melt occurred ph over the shelf was largely confined to a range of 7 9 8 1 and calcite and aragonite ranged from 1 5 to 3 0 and 0 8 to 2 0 respectively at the stations closest to river outflows aragonite was undersaturated in the water column from the surface to the bottom during the summer sea ice retreat high rates of primary production consumed dic in the mixed layer which increased ph and calcite and aragonite however calcite and aragonite decreased by 0 3 in the bottom waters over the middle and outer shelf over the northern shelf where export production is highest aragonite decreased by 0 35 and became highly undersaturated the observed suppression and undersaturation of calcite and aragonite in the eastern bering sea are correlated with anthropogenic carbon dioxide uptake into the ocean and will likely be exacerbated under business as usual emission scenarios therefore ocean acidification could threaten some benthic and pelagic calcifying organisms across the bering sea shelf in the coming decades

magnetic properties of tektites and other related impact glasses we present a comprehensive overview of the magnetic properties of the four known tektite fields and related fully melted impact glasses aouelloul belize darwin libyan desert and wabar glasses irghizites and atacamaites namely magnetic susceptibility and hysteresis properties as well as properties dependent on magnetic grain size tektites appear to be characterized by pure fe2 paramagnetism with ferromagnetic traces below 1 ppm the different tektite fields yield mostly non overlapping narrow susceptibility ranges belize and darwin glasses share similar characteristics on the other hand the other studied glasses have wider susceptibility ranges with median close to paramagnetism fe2 and fe3 but with a high susceptibility population bearing variable amounts of magnetite this signs a fundamental difference between tektites plus belize and darwin glasses and other studied glasses in terms of oxygen fugacity and heterogeneity during formation thus bringing new light to the formation processes of these materials it also appears that selecting the most magnetic glass samples allows to find impactor rich material opening new perspectives to identify the type of impactor responsible for the glass generation

coastal ocean co2 carbonic acid carbonate sediment system of the anthropocene 1 there is little doubt that human activities such as burning of fossil fuels and land use practices have changed and will continue to change the cycling of carbon in the global coastal ocean in the present study two biogeochemical box models were used to investigate the consequences of increasing atmospheric co2 and subsequent ocean acidification and increasing riverine transport of organic matter and nutrients arising from human activities on land on the global coastal ocean between the years 1700 and 2300 numerical simulations show that the net flux of co2 between coastal ocean surface water and the atmosphere is likely to change during this time from net evasion to net invasion owing to increasing atmospheric co2 increasing net ecosystem production arising from increasing nutrient loading to this region and decreasing net ecosystem calcification due to lower carbonate ion concentration and subsequent lower surface water saturation state with respect to carbonate minerals model calculations show that surface water saturation state with respect to calcite will decrease 73 by the year 2300 under a business as usual scenario which in concert with increasing temperature will cause overall biogenic calcification rate to decrease by 90 dissolution of carbonate minerals increased by 267 throughout the model simulation this increase was in part due to increased invasion of atmospheric co2 but mainly due to greater deposition and remineralization of land derived and in situ produced organic matter in the sediments producing co2 that caused pore water ph and carbonate saturation state to decrease this decrease in turn drove selective dissolution of metastable carbonate minerals as a consequence the relative carbonate composition of the sediments changed in favor of carbonate phases with lower solubility than that of an average 15 mol magnesian calcite phase model projected changes in surface water carbonate saturation state agree well with observations from the hawaiian ocean time series and the calculated air sea co2 exchange agrees well with a recent independent estimate of this flux derived from measurements from diverse coastal ecosystems scaled up to the global coastal ocean area

styles of lithospheric extension controlled by underplated mafic bodies abstract the role of underplated mafic bodies upmb in the localization of deformation is examined using a two dimensional thermo mechanical finite element model rheological heterogeneity brought about by the upmb is linked with the following two main physical effects the upmb material is assumed to have 1 an anomalous high temperature and 2 a mafic crustal rock composition that is intrinsically weaker than the mantle the thermal effect will disappear rather quickly but the rock composition can have an effect at any stage of extension we show that the upmb has a strong influence on the style of lithospheric extension which depends on the thermal condition of the uppermost mantle at the time when the upmb is emplaced since the strength contrast between the weakened and non weakened regions is the most important factor the upmb works more efficiently on the localization of deformation for a colder uppermost mantle dependence of the localization of deformation on the temperature and thickness of the upmb i e more significant localization for the upmb with higher temperature and greater thickness also depends on the thermal condition of the uppermost mantle however the width of the upmb has a strong influence on the localization for any thermal condition of the uppermost mantle a greater amount of thinning is distributed into a narrower weakened region such a model behaviour implies that various styles of lithospheric extension including inward or outward migration of deformation and asymmetric extension can be simply obtained by considering the emplacement of the upmb which also plays an important role in controlling the onset of continental break up

basalt magmatism along the passive continental margin of se brazil campos basin the se brazil passive continental margin is characterized by tholeiitic magmatism that is particularly widespread in the marginal campos basin facing the inland flood basalts of the adjacent parana basin campos magmatism is represented by early cretaceous ec 134 122 ma flood basalts and minor upper cretaceous early tertiary basalt flows and intrusives which were emplaced in a basin with attenuated crustal thickness 20 km petrography mineral chemistry wholerock geochemistry and sr nd isotope composition emphasize that the ec campos basalts have suffered extensive seawater interaction which caused enrichment in mgo feo total k2o rb and ba and depletion in sio2 and cao while zr nb y and ree remained virtually constant in samples with loss on ignition values less than 4 wt in general campos basalts have bulkrock chemistry similar to those of the inland parana tholeiites 140 130 ma with relatively low concentrations of incompatible elements and tio2 16 morb mid ocean ridge basalt mantle in simple binary mixing models on the whole the early cretaceous campos basalts appear as an easterly younger extension of the northern parana volcanism and probably erupted during early stages of the major riftingprocesses which caused continental thinning it is notable that in the campos marginal basin both the basalt magmatism contemporaneous with the continental break up as well as that which occurred after the s america africa separation appears substantially related to subcontinental lithosphere and a dupal like oib ocean island basalt e g tristan da cunha source components

occurrence of aragonite corrosive water in the north yellow sea near the yalu river estuary during a summer flood abstract to understand seawater caco3 saturation state arag for aragonite and cal for calcite dynamics in river dominated ocean margins we investigated the carbonate system and ancillary parameters in the north yellow sea near the yalu river estuary during and after a summer flood august and september 2013 respectively during the flood period nearshore arag ranged from 0 76 to 1 61 and cal ranged from 1 22 to 2 53 aragonite undersaturation values were associated with quite low salinity of 14 58 25 18 and a broad dissolved oxygen saturation range from 58 to 102 a week after the flood period aragonite undersaturated waters together with the estuarine plumes disappeared based on field data analyses and simplified model simulation we suggest that net community respiration remineralization and the dilution of riverine water discharge both contributed to the low caco3 saturation states

influences of riverine and upwelling waters on the coastal carbonate system off central chile and their ocean acidification implications a combined data set combining data from field campaigns and oceanographic cruises was used to ascertain the influence of both river discharges and upwelling processes covering spatial and temporal variation in dissolved inorganic carbon dic and aragonite saturation state this work was conducted in one of the most productive river influenced upwelling areas in the south pacific coasts 36 s additionally further work was also conducted to ascertain the contribution of different dic sources influencing the dynamics of dic along the land ocean range six sampling campaigns were conducted across seven stations at the biobio river basin covering approximately 200 km three research cruises were undertaken simultaneously covering the adjacent continental shelf including 12 sampling stations for hydrographic measurements additionally six stations were also sampled for chemical analyses covering summer winter and spring conditions over 2010 and 2011 our results evidenced that seaward extent of the river plume was more evident during the winter field campaign when highest riverine dic fluxes were observed the carbonate system along the river ocean continuum was very heterogeneous varying over spatial and temporal scales high dic and pco2 were observed in river areas with larger anthropogenic effects co2 supersaturation at the river plume was observed during all campaigns due to the influence of low ph river waters in winter spring and high pco2 upwelling waters in summer 13cdic evidenced that main dic sources along the river and river plume corresponded to the respiration of terrestrial organic matter we have linked this natural process to the carbonate saturation on the adjacent river influenced coastal area suggesting that aragonite undersaturation in surface subsurface waters is largely modulated by the influence of both river discharge and coastal upwelling events in this productive coastal area conditions of low aragonite might impact negatively physiological traits for marine organisms such as bivalves gastropods and crustaceans therefore local populations from river influenced sites could be inherently more tolerant to ocean acidification than organisms living in regions with lower aragonite variability

decadal changes in the aragonite and calcite saturation state of the pacific ocean 1 based on measurements from the woce jgofs global co2 survey the clivar co2 repeat hydrography program and the canadian line p survey we have observed an average decrease of 0 34 yr 1 in the saturation state of surface seawater in the pacific ocean with respect to aragonite and calcite the upward migrations of the aragonite and calcite saturation horizons averaging about 1 to 2 m yr 1 are the direct result of the uptake of anthropogenic co2 by the oceans and regional changes in circulation and biogeochemical processes the shoaling of the saturation horizon is regionally variable with more rapid shoaling in the south pacific where there is a larger uptake of anthropogenic co2 in some locations particularly in the north pacific subtropical gyre and in the california current the decadal changes in circulation can be the dominant factor in controlling the migration of the saturation horizon if co2 emissions continue as projected over the rest of this century the resulting changes in the marine carbonate system would mean that many coral reef systems in the pacific would no longer be able to sustain a sufficiently high rate of calcification to maintain the viability of these ecosystems as a whole and these changes perhaps could seriously impact the thousands of marine species that depend on them for survival

the combined effects of ocean acidification mixing and respiration on ph and carbonate saturation in an urbanized estuary puget sound is a large estuary complex in the u s pacific northwest that is home to a diverse and economically important ecosystem threatened by anthropogenic impacts associated with climate change urbanization and ocean acidification while ocean acidification has been studied in oceanic waters little is known regarding its status in estuaries anthropogenically acidified coastal waters upwelling along the western north american continental margin can enter puget sound through the strait of juan de fuca in order to study the combined effects of ocean acidification and other natural and anthropogenic processes on puget sound waters we made the first inorganic carbon measurements in this estuary on two survey cruises in february and august of 2008 observed ph and aragonite saturation state values in surface and subsurface waters were substantially lower in parts of puget sound than would be expected from anthropogenic carbon dioxide co2 uptake alone we estimate that ocean acidification can account for 24e49 of the ph decrease in the deep waters of the hood canal sub basin of puget sound relative to estimated pre industrial values the remaining change in ph between when seawater enters the sound and when it reaches this deep basin results from remineralization of organic matter due to natural or anthropogenically stimulated respiration processes within puget sound over time however the relative impact of ocean acidification could increase significantly accounting for 49e82 of the ph decrease in subsurface waters for a doubling of atmospheric co2 these changes may have profound impacts on the puget sound ecosystem over the next several decades these estimates suggest that the role ocean acidification will play in estuaries may be different from the open ocean published by elsevier ltd

rift brittle deformation of se brazilian continental margin kinematic analysis of onshore structures relative to the transfer and accommodation zones of southern campos basin abstract high resolution drone supported mapping and traditional field work were used to refine the hierarchy and kinematics of rift related faults in the basement rocks and early cretaceous mafic dikes onshore of the campos basin se brazil two sets of structures were identified the most significant fault set is ne sw oriented with predominantly normal displacement at mesoscale this fault set is arranged in a rhombic pattern interpreted here as a breached relay ramp system the rhombic pattern is a penetrative fabric from the thin section to regional scale the second order set of structures is an e w ese wnw system of normal faults with sinistral component these e w structures are oriented parallel with regional intrabasinal transfer zones associated with the earliest stages of campos basin s rift system the crosscutting relationship between the two fault sets and tholeiitic dikes implies that the ne sw fault set is the older feature but remained active until the final stages of rifting in this region as the second order fault set is older than the tholeiitic dikes paleostresses estimated from fault slip inversion method indicated that extension was originally nw se with formation of the e w transfer followed by ese wnw oblique opening associated with a relay ramp system and related accommodation zones

control of the rheological structure of the lithosphere on the inward migration of tectonic activity during continental rifting analogue models are used to analyse the parameters controlling the evolution of extensional deformation in continental rifts models are deformed in a centrifuge and simulate the continental lithosphere floating and extending above a low viscosity asthenosphere model results reproduce the typical evolution of deformation during continental narrow rifting with early activation of large boundary faults and basin subsidence followed by their abandonment and localization of tectonic activity in internal faults near the centre of the rift the experiments document the strong influence exerted by the thickness of both brittle and ductile crustal layers and syn rift sediment accumulation on the evolution of deformation namely on the amount of bulk extension preceding inward fault migration thin upper and or lower crust and absent or low syn rift sedimentation promote a rapid abandonment of boundary faults and a transition to in rift fault development for low amounts of extension conversely thick upper and or lower crust and high syn rift sediment accumulation favour prolonged slip on boundary faults and delayed development of internal faulting the experimental results suggest that the inward migration of faulting during extension of continental lithosphere results from the interplay between the ductile stresses acting at the base of the upper crust and the total resistance of this brittle layer

direct observations of basin wide acidification of the north pacific ocean 1 global ocean acidification is a prominent inexorable change associated with rising levels of atmospheric co 2 here we present the first basin wide direct observations of recently declining ph along with estimates of anthropogenic and non anthropogenic contributions to that signal along 152 w in the north pacific ocean 22 56 n ph changes between 1991 and 2006 were essentially zero below about 800 m depth however in the upper 500 m significant ph changes as large as 0 06 were observed anthropogenic and non anthropogenic contributions over the upper 800 m are estimated to be of similar magnitude in the surface mixed layer depths to 100 m the extent of ph change is consistent with that expected under conditions of seawater atmosphere equilibration with an average rate of change of 0 0017 yr future mixed layer changes can be expected to closely mirror changes in atmospheric co 2 with surface seawater ph continuing to fall as atmospheric co 2 rises

dynamics of fossil fuel co2 neutralization by marine caco3 a detailed model of the ocean circulation and carbon cycle was coupled to a mechanistic model of caco3 diagenesis in deep sea sediments to simulate the millennium scale response of the oceans to future fossil fuel co2 emissions to the atmosphere and deep sea simulations of deep sea injection of co2 show that caco3 dissolution is sensitive to passage of high co2 waters through the atlantic ocean but caco3 dissolution has a negligible impact on atmospheric pco2 or the atmospheric stabilization co2 emission in the coming centuries the ultimate fate of the fossil fuel co2 will be to react with caco3 on the seafloor and on land an initial caco3 dissolution spike reverses the net sedimentation rate in the ocean until it is attenuated by an enhanced vertical gradient of alkalinity after about 1000 years the magnitude of the initial spike is sensitive to assumptions about the kinetics for caco3 dissolution but subsequent behavior appears to be less model dependent neutralization by seafloor caco3 occurs on a timescale of 5 6 kyr and is limited to at most 60 70 of the fossil fuel release even if the fossil fuel release is smaller than the seafloor erodible inventory of caco3 additional neutralization by terrestrial caco3 restores a balance between caco3 weathering and seafloor accumulation on a timescale of 8 5 kyr while the deficit of seafloor caco3 the lysocline is replenished with an e folding timescale of approximately 18 kyr the final equilibrium with caco3 leaves 7 8 of the fossil fuel co2 remaining in the atmosphere to be neutralized by the silicate rock cycle on a time frame of hundreds of thousands of years

a new global marine magnetic anomaly data set the geophysical data system geodas stores more than 20 million magnetic measurements acquired over oceans and seas since the 1950s usually the original total field tf and magnetic anomaly values are both stored the anomaly results from the subtraction of the core and external magnetic field estimates from tf values the most recent international geomagnetic reference field models available at the time of the surveys were used to estimate the core field component these models were revised later external fields were estimated from magnetic observatory data however most of the measurements were not corrected for the external fields here we use comprehensive models to properly remove the core and external magnetic fields from all original tf measurements stored in the geodas besides a track by track analysis of each data is necessary mainly to correct or to remove many shifted values as well as to reduce the noise in some track lines two additional processes are applied to obtain a data set coherent over the world it includes an adjustment of long wavelength magnetic anomalies using the national geophysical data center ngdc 720 model plus a line leveling method which mainly reduced some inconsistencies between different surveys the root mean square of the crossover differences was reduced from 179 6 to 35 9 nt comparisons of magnetic anomaly maps before and after our treatment also highlight an improvement in the quality and the coherence of the data set this study will serve to build a new world digital magnetic anomaly map

climatological distribution of aragonite saturation state in the global oceans aragonite saturation state arag in surface and subsurface waters of the global oceans was calculated from up to date through the year of 2012 ocean station dissolved inorganic carbon dic and total alkalinity ta data surface arag in the open ocean was always supersaturated 1 ranging between 1 1 and 4 2 it was above 2 0 2 0 4 2 between 40 n and 40 s but decreased toward higher latitude to below 1 5 in polar areas the influences of water temperature on the ta dic ratio combined with the temperature effects on inorganic carbon equilibrium and apparent solubility product k sp explain the latitudinal differences in surface arag vertically arag was highest in the surface mixed layer higher hydrostatic pressure lower water temperature and more co2 buildup from biological activity in the absence of air sea gas exchange helped maintain lower arag in the deep ocean below the thermocline aerobic decomposition of organic matter along the pathway of global thermohaline circulation played an important role in controlling arag distributions seasonally surface arag above 30 latitudes was about 0 06 to 0 55 higher during warmer months than during colder months in the open ocean waters of both hemispheres decadal changes of arag in the atlantic and pacific oceans showed that arag in waters shallower than 100 m depth decreased by 0 10 0 09 0 40 0 37 yr 1 on average from the decade spanning 1989 1998 to the decade spanning 1998 2010

heterogeneous crust and upper mantle across the se brazilian highlands and the relationship to surface deformation as inferred from magnetotelluric imaging 1 we provide evidence for lateral structural zoning of the crust and uppermost mantle across the southeast brazilian highlands from two dimensional magnetotelluric mt imaging of a 250 km long nw se profile extending from the archaean sao francisco craton to near the atlantic coast our model shows the presence of an electrically resistive cover layer of variable thickness 2 20 km and an underlying 5 15 km thick conductive marker horizon atop a resistive segmented layer extending to 60 70 km depth two structurally different lithospheric provinces are suggested based on conductor geometry and lateral segmentation in the model the northwestern half of the profile is characterized by flat to shallowly dipping crustal conductors interpreted as a fold and thrust belt while the southeastern half consists of major steeply dipping lithospheric conductors with spatially coincident high amplitude magnetic anomalies interpreted as a strike slip fault belt the boundary between both provinces may be associated with a suture but lies 35 km nw of a previously suggested boundary between the occidental and oriental terranes the marker horizon is coincident with a low p wave velocity layer and appears to be raised by about 5 km across a 85 km wide belt hosting a neoproterozoic magmatic arc in the southeastern province we propose a link between basement heterogeneity and surface deformation in the region

abyssal water carbon 14 distribution and the age of the world oceans the carbon 14 distribution in the abyssal waters of the world oceans indicates replacement times for pacific indian and atlantic ocean deep waters more than 1500 meters deep of approximately 510 250 and 275 years respectively the deep waters of the entire world ocean are replaced on average every 500 years

coastal ocean and carbonate systems in the high co2 world of the anthropocene the behavior of the ocean carbon cycle has been and will continue to be modified by the increase in atmospheric co2 due to fossil fuel combustion and land use emissions of this gas the consequences of a high co2 world and increasing riverine transport of organic matter and nutrients arising from human activities were investigated by means of two biogeochemical box models model numerical simulations ranging from the year 1700 to 2300 show that the global coastal ocean changes from a net source to a net sink of atmospheric co2 over time in the 18th and 19th centuries the direction of the co2 flux was from coastal surface waters to the atmosphere whereas at present or in the near future the net co2 flux is into coastal surface waters these results agree well with recent syntheses of measurements of air sea co2 exchange fluxes from various coastal ocean environments the model calculations also show that coastal ocean surface water carbonate saturation state would decrease 46 percent by the year 2100 and 73 percent by 2300 observational evidence from the pacific and atlantic oceans shows that the carbonate saturation state of surface ocean waters has already declined during recent decades for atolls and other semi enclosed carbonate systems the rate of decline depends strongly on the residence time of the water in the system based on the experimentally observed positive relationship between saturation state and calcification rate for many calcifying organisms biogenic production of caco3 may decrease by 42 percent by the year 2100 and by 85 to 90 percent by 2300 relative to its value of about 24 1012 moles c yr in the year 2000 if the predicted change in carbonate production were to occur along with rising temperatures it would make it difficult for coral reef and other carbonate systems to exist as we know them now into future centuries because high latitude cold water carbonates presently occur in waters closer to saturation with respect to carbonate minerals than the more strongly supersaturated waters of the lower latitudes it might be anticipated that the cool water carbonate systems might feel the effects of rising atmospheric co2 and temperature before those at lower latitudes in addition modeling results show that the carbonate saturation state of coastal sediment pore water will decrease in the future owing to a decreasing pore water ph and increasing co2 concentrations attributable to greater deposition and remineralization of land derived and in situ produced organic matter in sediments the lowered carbonate saturation state drives selective dissolution of metastable carbonate minerals while a metastable equilibrium is maintained between the pore water and the most soluble carbonate phase present in the sediments in the future the average composition of carbonate sediments and cements may change as the more soluble mg calcites and aragonite are preferentially dissolved and phases of lower solubility such as calcites with lower magnesium content increase in percentage abundance in the sediments

detecting the progression of ocean acidification from the saturation state of caco3 in the subtropical south pacific progression of ocean acidification in the subtropical south pacific was investigated by using high quality data from trans pacific zonal section at 17 s world ocean circulation experiment section p21 collected in 1994 and 2009 during this 15 year period the caco3 saturation state of seawater with respect to calcite cal and aragonite arg in the upper water column 400 dbar decreased at rates of 0 037 a 1 and 0 025 a 1 respectively east of 145 w longitude these rates are among the fastest in the world s oceans in contrast at longitudes 170 e 145 w cal and arg decreased relatively slowly at 0 008 a 1 and 0 005 a 1 respectively the arg saturation horizon occurred at a depth of about 1200 dbar at the westernmost end of the section and shoaled eastward to about 20 dbar from 1994 to 2009 it migrated upward at a rate of 5 2 dbar a 1 west of 145 w decomposition of the temporal changes of showed that the accumulation of anthropogenic co2 in the ocean accounted for more than half of the more rapid rate of decline of in the eastern section was attributable to a relatively large contribution of organic matter remineralization whereas the slower rate in the central section was attributed to a decrease of anthropogenic co2 uptake caused by rising water temperatures an important finding of this study was that acidification of the upper water column was enhanced by processes related to the oxygen minimum zone in the eastern subtropical south pacific ocean

production and accumulation of calcium carbonate in the ocean budget of a nonsteady state present day production of caco3 in tne world ocean is calculated to be about 5 billion tons bt per year of which about 3 bt accumulate in sediments the other 40 is dissolved nearly half of the carbonate sediment accumulates on reefs banks and tropical shelves and consists largely of metastable aragonite and magnesian calcite deep sea carbonates predominantly calcitic coccoliths and planktonic foraminifera have orders of magnitude lower productivity and accumulation rates than shallow water carbonates but they cover orders of magnitude larger basin area twice as much calcium is removed from the oceans by present day carbonate accumulation as is estimated to be brought in by rivers and hydrothermal activity 1 6 bt suggesting that outputs have been overestimated or inputs underestimated that one or more other inputs have not been identified and or that the oceans are not presently in steady state one missing calcium source might be groundwater although its present day input is probably much smaller than that of rivers if as seems likely caco3 accumulation presently exceeds terrestial and hydrothermal input this imbalance presumably is offset by decreased accumulation and increased input during lowered sea level shallow water accumulation decreases by an order of magnitude with a 100 m drop in sea level while groundwater influx increases because of heightened piezometric head and the diagenesis of metastable aragonite and magnesian calcite from subaerially exposed shallow water carbonates

a first look at factors affecting aragonite compensation depth in the eastern arabian sea abstract water column measurements suggest shoaling of aragonite saturation depths asd throughout the world oceans due to increase in greenhouse gas concentration past records of aragonite saturation state under different climatic conditions are required to assess the impact of climatic changes on shoaling deepening of asd the preservation state of organisms having aragonite skeletons is used to assess the past changes in aragonite saturation depths with respect to the modern asd here for the first time we delineate and discuss the factors that affect the modern aragonite compensation depth acd in the eastern arabian sea by using pteropod abundance in the surface sediments a total of 78 spade core top samples collected along seven latitudinal transects covering the continental shelf slope and abyssal region of the eastern arabian sea were used pteropods were picked from coarse fraction 63 m based on the pteropod preservation we report that in the eastern arabian sea acd lies at a water depth of 525 m which matches with the chemically defined aragonite saturation depth we further report that the acd shoals from north to south the zone of high pteropod abundance coincides with low corg the increase in pteropod abundance in the outer shelf region coincides with the drop in dissolved oxygen concentration the deeper limit of pteropod abundance lies in the center of the oxygen minimum zone with higher corg therefore we suggest that the pteropod abundance in the eastern arabian sea is not always related with the lower dissolved oxygen but is strongly influenced by corg this first report of the pteropod based aragonite compensation depth estimates from the eastern arabian sea will help in assessing future changes in acd under the influence of anthropogenic green house gas emissions

foraminiferal proxy response to ocean temperature variability and acidification over the last 150 years in the santa barbara basin california abstract the last 150 years on the california margin have been marked by high variability in precipitation temperature sea surface temperature and ocean chemistry in response to both natural and anthropogenic changes deciphering climate history from ocean sediments is dependent on our understanding of the various influences on marine proxies sediment from santa barbara basin sbb california box core spr0901 10bc provides an opportunity to compare multiple marine proxies with instrumental records of climate of the past 150 years and extend them beyond the historical record here we use three planktonic foraminiferal proxies 18ocalcite mg ca and size normalized shell weight to reconstruct the surface temperature and 18owater in sbb california at near annual resolution from ad 1850 2000 results indicate that globigerina bulloides mg ca reflects the instrumental temperature trends over the last 150 years with average mg ca temperatures approximately 2 c lower than instrumental values due to the slightly deeper habitat preference of g bulloides similarly temperature is the dominant control on g bulloides 18ocalcite and both mg ca and 18ocalcite reflect variability consistent with changes in the intensification of enso over the past 150 years shell weights of the planktic foraminifer g bulloides are inversely correlated with historical sea surface temperatures over the last 150 years in sbb sediments greater shell weight associated with cooler surface ocean temperatures does not support the anticipated relationship between coastal upwelling of cool low ph water and shell thinning due to co 3 2 undersaturation however in contrast to the previous 130 years g bulloides shells deposited on the sea floor since the late 1970s exhibit a distinctive smooth shell structure indicative of partial dissolution we hypothesize that a mid 1970s shift in intermediate water flow from predominantly equatorward to anomalously poleward led to the influx of relatively corrosive bottom water into sbb with subsequent carbonate dissolution at the sediment water interface

a novel determination of calcite dissolution kinetics in seawater we present a novel determination of the dissolution kinetics of inorganic calcite in seawater we dissolved 13 c labeled calcite in unlabeled seawater and traced the evolving 13 c composition of the fluid over time to establish dissolution rates this method provides sensitive determinations of dissolution rate which we couple with tight constraints on both seawater saturation state and surface area of the dissolving minerals we have determined dissolution rates for two different abiotic calcite materials and three different grain sizes near equilibrium dissolution rates are highly nonlinear and are well normalized by geometric surface area giving an empirical dissolution rate dependence on saturation state of rate g cm 2 day 7 2 0 6 10 4 1 3 9 0 1 this result substantiates the non linear response of calcite dissolution to undersaturation the bulk dissolution rate constant calculated here is in excellent agreement with those determined in far from equilibrium and dilute solution experiments plots of dissolution versus undersaturation indicates the presence of at least two dissolution mechanisms implying a criticality in the calcite seawater system finally our new rate determination has implications for modeling of pelagic and seafloor dissolution nonlinear dissolution kinetics in a simple 1 d lysocline model indicate a possible transition from kinetic to diffusive control with increasing water depth and also confirm the importance of respiration driven dissolution in setting the shape of the calcite lysocline

calcium carbonate budget in the atlantic ocean based on water column inorganic carbon chemistry 1 recent independent lines of evidence suggest that the dissolution of calcium carbonate caco3 particles is substantial in the upper ocean above the calcite 100 saturation horizon this shallow water dissolution of carbonate particles is in contrast with the current paradigm of the conservative nature of pelagic caco3 at shallow water depths here we use more than 20 000 sets of carbon measurements in conjunction with cfc and 14c data from the woce jgofs oaces global co2 survey to estimate in situ dissolution rates of caco3 in the atlantic ocean a dissolution rate is estimated from changes in alkalinity as a parcel of water ages along an isopycnal surface the in situ caco3 dissolution increases rapidly at the aragonite 100 saturation horizon estimated dissolution rates north of 40on are generally higher than the rates to the south which is partly attributable to the production of exported caco3 being higher in the north atlantic than in the south atlantic as more caco3 particles move down the water column more particles are available for in situ dissolution the total water column caco3 dissolution rate in the atlantic ocean is determined on an annual basis by integrating estimated dissolution rates throughout the entire water column and correcting for alkalinity input of approximately 5 6 1012 mol c yr 1 from caco3 rich sediments the resulting water column dissolution rate of caco3 for the atlantic ocean is approximately 11 1 1012 mol c yr 1 this corresponds to about 31 of a recent estimate 35 8 1012 mol c yr 1 of net caco3 production by lee 2001 for the same area our calculation using a large amount of high quality water column alkalinity data provides the first basin scale estimate of the caco3 budget for the atlantic ocean

co2 radiative forcing and intertropical convergence zone influences on western pacific warm pool climate over the past 400 ka abstract the western pacific warm pool wpwp is an important heat source for the atmospheric circulation and influences climate conditions worldwide estimating wpwp sensitivity to past radiative forcing perturbations is important for understanding the magnitudes and patterns of current and projected tropical climate change here we present a new mg ca based sea surface temperature sst reconstruction over the past 400 ka from the bismarck sea off papua new guinea along with benthic foraminiferal 18o records and a transient intermediate complexity earth system model simulation the mg ca sst record exhibits a close similarity with atmospheric co2 content for the whole study period our model analysis demonstrates that greenhouse gas forcing is the primary driver for glacial interglacial sst changes in the entire wpwp region mg ca sst in the bismarck sea also includes a weaker precessional component which covaries with reconstructed and simulated local precipitation and simulated surface currents we propose that orbitally driven latitudinal shifts of the intertropical convergence zone and oceanic heat advection are responsible for this residual sst variability on glacial timescales the reconstructed wpwp surface temperature changes over the past 400 ka are highly correlated with east antarctic air temperature variations the strong effect of greenhouse gas forcings on both records and on global mean temperature variability allows us to determine a scaling factor of 1 1 5 between reconstructed wpwp temperature anomalies and estimates of the global mean temperature

deep structures and breakup along volcanic rifted margins insights from integrated studies along the outer voring basin norway three dimensional multichannel seismic survey and well data allows a deeper insight into rifting mechanisms and crustal structure of the norwegian volcanic rifted margin a surprising high velocity lower crustal dome marked by a strong amplitude reflection t reflection is described below the north gjallar ridge ngr near the volcanic plateau formed during the late paleocene early eocene breakup faulting along the ngr occurs during early campanian paleocene and is controlled by the crustal dome the t reflection was previously related to either the top of mafic underplated crust or soft lower crust updomed during the continental breakup the influence and timing of the crustal dome on the basin structure shows clearly that the dome predates the continental breakup based on the structural relationship and the results of the modelling it is therefore concluded that the t reflection does not necessarily originate from an anomalous tertiary magmatic event related to the breakup underplated material but could be also partly attributed to pre breakup mafic material or and inherited high pressure granulite eclogite rocks in the continental domain q 2004 elsevier ltd all rights reserved

the araa uaa west congo orogen in brazil an overview of a confined orogen formed during gondwanaland assembly abstract the neoproterozoic adamastor brazilide ocean was generated during the breakup of the rodinia supercontinent and remnants of its oceanic lithosphere have been found in the brasiliano pan african orogenic system that includes the aracuai west congo brasilia ribeira kaoko dom feliciano damara and gariep belts the aracuai and the west congo belts are counterparts of the same neoproterozoic orogen the first belt comprises two thirds of the aracuai west congo orogen this orogen is rather unique owing to its confined nature within the embayment outlined by the sao francisco and congo cratons in spite of this the presence of ophiolitic remnants and a calc alkaline magmatic arc indicate that the basin orogen evolution comprise both oceanic spreading and consumption it is assumed that coeval paramirim and sangha aulacogens played a key role by making room for the aracuai west congo basin sedimentary successions record all major stages of a basin that evolved from continental rift when glaciation related sedimentation was very significant to passive margin rifting started around 1 0 0 9 ga the oceanic stage is constrained by an ophiolitic remnant dated at 0 8 ga if the cratonic bridge that once linked the sao francisco and congo palaeocontinental regions did not hinder the opening of an ocean basin it certainly limited its width as a consequence only a narrow oceanic lithosphere was generated and it was subducted afterwards this is also suggested by orogenic calc alkaline granitoids occuping a small area of the orogen geochronological data for pre syn and late collisional granitoids indicate that the orogenic stage lasted from 625 ma to 570 ma a period of magmatic quiescence was followed by intrusion of postcollisional plutons at 535 500 ma the features of the aracuai west congo orogen suggest the development of a complete wilson cycle in a branch of the adamastor ocean which can be interpreted as a gulf with limited generation of oceanic lithosphere

migration why doesn t it work for deep continental data summary conventional migration of deep seismic reflection data often produces disappointingly poor results even when the original unmigrated data are of high quality and are relatively noise free surprisingly deep data often subjectively appear to be best migrated at velocities which are up to 50 less than appropriate interval velocities derived from crustal refraction experiments or directly from stacking velocities the explanation for this behaviour is that near surface features distort and attenuate the seismic wave field and produce apparent discontinuities in deep reflections since these discontinuities are spurious they are not associated with the appropriate large diffractions which real discontinuities at depth would produce during the process of migration reflections are invented in order to cancel out the missing diffractions thereby producing a smiley section which appears overmigrated since the lateral extent of individual smiles increases with increasing migration velocity increasing two way time and increasing seismic wavelength the effect is almost unnoticeable on conventional shallow seismic data but is overwhelming for deep crustal data

chemical and biological impacts of ocean acidification along the west coast of north america abstract the continental shelf region off the west coast of north america is seasonally exposed to water with a low aragonite saturation state by coastal upwelling of co2 rich waters to date the spatial and temporal distribution of anthropogenic co2 canth within the co2 rich waters is largely unknown here we adapt the multiple linear regression approach to utilize the go ship repeat hydrography data from the northeast pacific to establish an annually updated relationship between canth and potential density this relationship was then used with the noaa ocean acidification program west coast ocean acidification wcoa cruise data sets from 2007 2011 2012 and 2013 to determine the spatial variations of canth in the upwelled water our results show large spatial differences in canth in surface waters along the coast with the lowest values 37 55 mol kg 1 in strong upwelling regions off southern oregon and northern california and higher values 51 63 mol kg 1 to the north and south of this region coastal dissolved inorganic carbon concentrations are also elevated due to a natural remineralized component cbio which represents carbon accumulated through net respiration in the seawater that has not yet degassed to the atmosphere average surface canth is almost twice the surface remineralized component in contrast canth is only about one third and one fifth of the remineralized component at 50 m and 100 m depth respectively uptake of canth has caused the aragonite saturation horizon to shoal by approximately 30 50 m since the preindustrial period so that undersaturated waters are well within the regions of the continental shelf that affect the shell dissolution of living pteropods our data show that the most severe biological impacts occur in the nearshore waters where corrosive waters are closest to the surface since the pre industrial times pteropod shell dissolution has on average increased approximately 19 26 in both nearshore and offshore waters

rifted margin architecture and crustal rheology reviewing iberia newfoundland central south atlantic and south china sea abstract crustal rheology controls the style of rifting and ultimately the architecture of rifted margins here we review the formation of three magma poor margin pairs iberia newfoundland the central segment of the south atlantic rift and the south china sea by integrating observational data into a numerical forward modelling framework we utilise a 2d version of the finite element code slim3d which includes nonlinear temperature and stress dependent elasto visco plastic rheology and is able to reproduce a wide range of rift related deformation processes such as flexure lower crustal flow and faulting extension in cold strong or thin crust is accommodated by brittle faults and ductile shear zones that facilitate narrow rifts with asymmetric fault geometries hot weak or thick continental crust is dominated by ductile deformation and often extends symmetrically into a wide rift system this simple recipe provides the standard framework to understand initial rift geometry however it is insufficient to account for the dynamics of intermediate and late rift stages that shape the final margin architecture asymmetric conjugate margins where one side is wide and the other narrow can be formed via both wide and narrow rift styles which we reproduce with weak and strong crustal rheologies respectively exemplified by the iberia newfoundland conjugates and the central south atlantic we define three characteristic rift phases an initial phase of simultaneous faulting an intermediate phase of rift migration that involves sequential fault activity and finally the breakup phase crustal rheology plays an overarching role in governing the dynamics of these asymmetric margins we illustrate that weak rheologies generally prolong the phase of simultaneous faulting while rift migration is enabled by initial fault asymmetry as well as relatively weak crust formation of the predominantly symmetric and wide margins of the south china sea was controlled by extraordinarily weak crust that extended the phase of simultaneous faulting until breakup the weak crustal rheology of this region relates to the south china sea s pre rift history where plate convergence lead to crustal thickening and magmatic additions in a back arc regime shortly before the onset of rifting

carbonate mineral saturation states along the u s east coast to assess the impact of ocean acidification on the carbonate chemistry of the shelf waters off the southeastern united states south atlantic bight sab we measured carbonate mineral saturation states from january 2005 to may 2006 the findings reveal that aragonite varag 2 6 4 0 and calcite vcal 4 1 6 0 saturation states were considerably higher than those recently reported along the west coast of north america different water mass age between the atlantic and pacific oceans during global ocean circulation is the primary reason for the higher carbonate mineral saturation states in the sab than along the west coast the contrasting water temperatures in the two coasts contribute to such differences both upwelling and freshwater discharge also play important roles in controlling saturation state carbonate mineral saturation in the surface water of the west coast is strongly controlled by the upwelling of high salinity low temperature low oxygen and low ph deep water in comparison saturation states in the surface water of the sab coast are rarely affected by upwelling instead they are strongly influenced by the input of low saturation state water from rivers continued increases of atmospheric co2 under the intergovernmental panel on climate change b1 emission scenario will decrease the carbonate mineral saturation states by up to 40 by the end of this century and aragonite will approach undersaturation near the coast

factors influencing the degree of saturation of the surface and intermediate waters of the north pacific ocean with respect to aragonite new carbonate chemistry data obtained during a 1982 cruise have been combined with earlier ge osecs and indopac data to determine the degree of aragonite saturation of surface and intermediate waters of the north pacific large gradients in saturation state occur in the region of the subarctic front in the north south direction and across the subtropical gyre in the east west direction these gradients are primarily due to the extensive mixing that occurs in the intermediate waters of the western north pacific the major variations in saturation state were primarily related to the carbonate ion concentration which in turn is primarily a function of mixing and biological processes the present aragonite saturation depth at our northernmost station in the western north pacific was calculated to be within 120 m of the surface this result was directly corroborated by observations of aragonite dissolution under in vitro conditions our calculations show that one possible effect of fossil fuel derived co2 on the surface of the north pacific will be a steady progression of undersaturation from the northern to southern and western areas with the first sign of undersaturation possibly occurring as early as the second half of the next century

transformations to granular zircon revealed twinning reidite and zro2 in shocked zircon from meteor crater arizona usa granular zircon in impact environments has long been recognized but remains poorly understood due to lack of experimental data to identify mechanisms involved in its genesis meteor crater in arizona usa contains abundant evidence of shock metamorphism including shocked quartz the high pressure polymorphs coesite and stishovite diaplectic sio2 glass and lechatelierite fused sio2 here we report the presence of granular zircon a new shocked mineral discovery at meteor crater that preserve critical orientation evidence of specific transformations that occurred during formation at extreme impact conditions the zircon grains occur as aggregates of sub micrometer neoblasts in highly shocked coconino sandstone cs comprised of lechatelierite electron backscatter diffraction shows that each grain consists of multiple domains some with boundaries disoriented by 65 around a known 112 shock twin orientation other domains have 001 in alignment with 110 of neighboring domains consistent with the former presence of the high pressure zrsio4 polymorph reidite additionally nearly all zircon preserve zro2 sio2 providing evidence of partial dissociation the genesis of cs granular zircon started with detrital zircon that experienced shock twinning and reidite formation at pressures from 20 to 30 gpa ultimately yielding a phase that retained crystallographic memory this phase subsequently recrystallized to systematically oriented zircon neoblasts and in some areas partially dissociated to zro2 the lechatelierite matrix experimentally constrained to form at 2000 c provided the ultrahigh temperature environment for zircon dissociation 1670 c and neoblast formation the capacity of granular zircon to preserve a cumulative pressure temperature record has not been recognized previously and provides a new method for investigating histories of impact related mineral transformations in the crust at conditions far beyond those at which most rocks melt

how does the continental crust thin in a hyperextended rifted margin insights from the iberia margin the discovery of hyperthinned continental crust and exhumed mantle on present day deep water rifted margins leads to two fundamental questions 1 in detail how does the crust thin in extension and 2 what controls extreme crustal thinning and mantle exhumation reflection and refraction seismic lines across the iberian margin show decoupling levels in the crust cut by structures that eventually transfer deformation to mantle levels the region of decoupled extension appears to be more broadly distributed on the northern iberian margin and more localized on the southern margin based on drill hole data the transition from decoupled to coupled deformation occurred during tithonian time ca 145 ma this evolution from decoupled to coupled deformation may help explain the crustal architecture of the iberian margin an apparent delay of subsidence across the hyperextended coupled zone of the iberian margin may indicate that crustal thinning had to occur simultaneously with lithospheric necking and the advection of heat related to lithospheric mantle thinning

past and future evolution of the marine carbonate system in a coastal zone of the northern antarctic peninsula abstract it is arduous to gather a good spatial and temporal dataset of marine carbonate properties especially in the southern ocean in this study we have reconstructed the carbonate system in the gerlache strait a coastal zone of the northern antarctic peninsula we also analyzed the impact of ocean acidification by calculating the tipping points of the calcium carbonate saturation states and ph i e when saturation state and ph goes below one and 7 respectively hydrographic and carbonate data from three distinct data sets goal 2013 2016 fruela 1996 and world ocean database 1965 2004 have been joined and used to reconstruct the carbonate system from the past 50 years temporal annual mean trends were determined depending on the water column depth layer the northern gerlache strait showed a significant increasing trend of total inorganic carbon concentrations 1 0024 0 34 mol kg 1 and related ph decreasing trend 0 0026 0 0009 sws in the surface mixed layer 60 m the properties variability is relatively different magnitudes and signs between the northern and southern sectors of the gerlache strait which indicate that adjacent regions to the gerlache strait to the southwest and north respectively may major influence the regional carbonate dynamics results also show that episodic under saturation conditions in relation to aragonite within the surface mixed layer may already occur especially in regions close to large glaciers

how preexisting weaknesses control the style of continental breakup continental breakup is a highly variable process differences occur in the relative timing and extent of volcanism uplift and graben formation as well as in the mode and amount of continental extension before breakup we propose a model which reconciles this variability with the previously recognized tendency for breakup to occur along preexisting weak trends continental lithosphere is viewed as a composite material composed of two strong layers one in the upper mantle and one in the middle crust finite element simulation indicates that extensional failure at weaknesses in the mantle causes concentrated extension in the mantle and diffuse extension in the crust this leads to early melt segregation and volcanism margin uplift during the late stages of the extension process and relatively narrow symmetrical extended margins in contrast failure at weaknesses in the crustal strong zone causes focused extension in the crust and diffuse extension in the mantle this produces initial graben formation cooling in the lower crust and upper mantle and broad asymmetrical extended margins volcanism only occurs late in the process failure at laterally offset weaknesses within both strong layers leads to a deformation pattern dominated simple shear thus differences in the prerift configuration of the continental lithosphere can control the overall style of continental breakup

crustal thickening in an extensional regime application to the mid norwegian voring margin abstract the structure of the mid norwegian volcanic voring margin at the onset of the maastrichtian paleocene extension phase reflects the cumulative effect of earlier consecutive rifting events lateral structural differences present on the margin at that time are a consequence of migration of the location of maximum extension in time between norway and greenland the most important imprints moho depth thermal structure of these events on the lithosphere are incorporated in a numerical simulation of the final extension phase we focus on a possible mechanism of formation of the voring marginal high and address the relationship between spatial and temporal evolution of crustal thinning and thickening uplift of the surface and strength of the lithosphere it is found that the voring basin formed the strongest part of the margin which explains why the maastrichtian paleocene rift axis was not located here but instead jumped westward with respect to the earlier rift axes locations the modeling study predicts that local crustal thickening during extension can be expected when large lateral thermal variations are present in the lithosphere at the onset of extension negative buoyancy induced by lateral temperature differences increases downwelling adjacent to the rifting zone convergence of material at the particular part of the margin is mainly taken up by the lower crust the model shows that during the final phase of extension the crust in the voring marginal high area was thickened and the surface uplifted it is likely that this dynamic process and the effects of magmatic intrusions both acted in concert to form the marginal high

climate variability in the north pacific thermocline diagnosed from oxygen measurements an update based on the u s clivar co2 repeat hydrography cruises 1 new observations of oxygen variability in the north pacific ocean are reported on the basis of comparison of the u s climate variability and predictability and carbon clivar co2 repeat hydrography sections conducted along 30 n 2004 and 152 w 2006 with the earlier world ocean circulation experiment woce data and other cruises along these sections the largest changes in apparent oxygen utilization aou continue to occur as found in earlier north pacific repeat section analyses within the thermocline on 26 6 kg m 3 which is the densest isopycnal to outcrop in the open north pacific in climatological data in the northeastern north pacific along 152 w where a total of five cruises 1980 1984 1991 1997 and 2006 spanning a period of 26 years are available the aou changes correspond to an overall increase in aou on 26 6 kg m 3 from the 1980s early 1990s to 2006 however from 1997 to 2006 a decrease in aou is observed within the boundary region between the subtropical and subpolar gyres at 40 45 n along the center axis of the subtropical gyre at 30 n where two cruises are available 1994 and 2004 aou has also substantially increased on 26 6 kg m 3 from 1994 to 2004 in the eastern part of the section the repeat section data along 152 w and 30 n are consistent with a pattern of decadal scale ventilation anomalies that originate in the northwestern pacific possibly through variability including cessation of the 26 6 kg m 3 outcrop travel eastward along the subtropical subpolar gyre boundary and enter the northern portion of the subtropical gyre along the way for the 152 w aou data within the gyre boundary region 40 45 n good agreement exists with the close by time series data from ocean station p 50 n 145 w where a bidecadal cycle in aou has been observed in contrast a sensible correlation with the pacific decadal oscillation could not be found

atmospheric co2 stabilization and ocean acidification 1 we use a coupled climate carbon cycle model to examine the consequences of stabilizing atmospheric co2 at different levels for ocean chemistry our simulations show the potential for major damage to at least some ocean ecosystems at atmospheric co2 stabilization levels as low as 450 ppm before the industrial revolution more than 98 of corals reefs were surrounded by waters that were 3 5 times saturated with respect to their skeleton materials aragonite if atmospheric co2 is stabilized at 450 ppm only 8 of existing coral reefs will be surrounded by water with this saturation level also at this co2 level 7 of the ocean south of 60 s will become undersaturated with respect to aragonite and parts of the high latitude ocean will experience a decrease in ph by more than 0 2 units results presented here provide an independent and additional basis for choosing targets of atmospheric co2 stabilization levels

rift zone magmatism petrology of basaltic rocks transitional from cfb to morb southeastern brazil margin compositions of basaltic samples from the southeastern brazil passive margin 18 24 s depict the change from continental to oceanic lithosphere during the opening of the south atlantic ocean samples studied range from 138 to 105 m y old and are from 12 petrobras drill cores recovered from the coastline to about 150 km offshore in the espirito santo campos and santos basins compositions vary ranging for example from 49 54 wt sio2 0 5 3 0 wt tio2 0 6 5 0 feo mgo and 1 6 la yb n but can be grouped i basalts enriched in incompatible elements such as k some k2o 2 0 wt rb 18 ppm zr 120 ppm and lree some feo 16 wt most with sio2 51 54 wt and resembling serra geral continental flood basalts sg cfb of southern brazil ii basalts less enriched or transitional in incompatible elements having k2o 30

processes of multibathyal aragonite undersaturation in the arctic ocean during three years of study 2010 2012 the western arctic ocean was found to have unique aragonite saturation profiles with up to three distinct aragonite undersaturation zones this complexity is produced as inflow of atlantic and pacific derived water masses mix with arctic derived waters which are further modified by physiochemical and biological processes the shallowest aragonite undersaturation zone from the surface to 30 m depth is characterized by relatively low alkalinity and other dissolved ions besides local influence of biological processes on aragonite undersaturation of shallow coastal waters the nature of this zone is consistent with dilution by sea ice melt and invasion of anthropogenic co2 from the atmosphere a second undersaturated zone at 90 220 m depth salinity 31 8 35 4 occurs within the arctic halocline and is characterized by elevated pco2 and nutrients the nature of this horizon is consistent with remineralization of organic matter on shallow continental shelves bordering the canada basin and the input of the nutrients and co2 entrained by currents from the pacific inlet finally the deepest aragonite undersaturation zone is at greater than 2000 m depth and is controlled by similar processes as deep aragonite saturation horizons in the atlantic and pacific oceans the comparatively shallow depth of this deepest aragonite saturation horizon in the arctic is maintained by relatively low temperatures and stable chemical composition understanding the mechanisms controlling the distribution of these aragonite undersaturation zones and the timescales over which they operate will be crucial to refine predictive models this article is protected by copyright all rights reserved

coral reefs may start dissolving when atmospheric co2 doubles 1 calcification rates in stony corals are expected to decline significantly in the near future due to ocean acidification in this study we provide a global estimate of the decline in calcification of coral reefs as a result of increase in sea surface temperature and partial pressure of co2 this estimate unlike previously reported estimates is based on an empirical rate law developed from field observations for gross community calcification as a function of aragonite degree of saturation arag sea surface temperature and live coral cover calcification rates were calculated for more than 9 000 reef locations using model values of arag and sea surface temperature at different levels of atmospheric co2 the maps we produced show that by the time atmospheric partial pressure of co2 will reach 560 ppm all coral reefs will cease to grow and start to dissolve

impact of the ocean carbonate chemistry on living foraminiferal shell weight comment on carbonate ion concentration in glacial age deep waters of the caribbean sea by w s broecker and e clark broecker and clark 2002 use the size normalized weight of planktic foraminifera to estimate the carbonate ion concentration co3 of atlantic glacial upper deep water this method was introduced by lohmann 1995 and is based on the fact that within a defined size fraction dissolution decreases shell weight in proportion to the degree of undersaturation with respect to caco3 based on the following assumptions 1 the thickness of the foraminiferal shell wall does not depend on growth conditions 2 the saturation co3 for calcite co3 sat increases by 20 mol kg 1 km 1 broecker and clark 2001 3 the weight loss slope is universal and ca 0 3 g mol kg 1 1 broecker and clark 2001 4 the offset between the bottom water and pore water co3 was the same during glacial time as during the holocene broecker and clark 2002 calculate that the co3 of atlantic glacial upper deep water was 14 mol kg 1 higher than during the holocene although they recognize that some of their assumptions are not strictly valid they do not assess the impact of those assumptions on their co3 estimate here we comment on several of those assumptions and attempt to quantify their impact on broecker and clark s 2002 calculations

architecture and tectono magmatic evolution of the campos rifted margin control of oct structure by basement inheritance abstract the formation of rifted margins involves the deformation of pre existing lithosphere whose rheological and mechanical behavior during extension is complex since it is the product of numerous earlier tectonic events in this work we investigate the campos rifted margin crm architecture with the aim of exploring the role of basement inheritance and early magmatism on margin evolution we present a new compilation of high resolution aeromagnetic data integrated with seismic interpretation and crustal thickness from 3d gravity inversion to resolve margin architecture ocean continent transition oct structure and the oceanward extent of continental basement we examine the lateral variation of crustal rheology necking geometry and rift segmentation revealing striking spatial heterogeneities that separate three distinct sectors along the campos margin the basement of the campos rifted margin consists of precambrian eo paleozoic ribeira belt rb and the easternmost cabo frio tectonic domain cftd whose neoproterozoic cambrian nappes and thrusts are well preserved offshore and give a rheologically layered crust this pre rift basement configuration along with the mesozoic magmatism has resulted in different crustal responses to extension which vary from north to south it influenced the temporal and spatial distribution of deformation and as a consequence the necking geometry subsidence and sedimentary evolution of the margin we show that the campos basin evolution was controlled by crustal inheritance corresponding to that observed in onshore basement terranes the more massive basement of the northern campos basin can be correlated with the post collisional cambro ordovician magmatic province of the aracuai belt that partially obliterated the earlier orogenic structures the lack of a structured crust localized the strain generating the observed narrow necking zone in addition its more mafic composition resulted in a competent crust which also influenced the rifting processes in contrast the basement of the central and southern campos margin represented by the cabo frio tectonic domain is structurally and petrologically distinct from the aracuai belt and has layered orogenic crust which responded differently to rifting stresses forming the observed wide necking zone we propose that the campos rifted margin evolved from a pre rift complex inherited rheology which dominated the first stages of rifting however once the crust was highly extended the deformation was nearly synchronous regionally leading to giant salt basin formation and breakup

biogeochemical generation of dissolved inorganic carbon and nitrogen in the north branch of inner changjiang estuary in a dry season abstract we investigated the surface water carbonate system nutrients and relevant hydrochemical parameters in the inner changjiang yangtze river estuary in early spring 2009 and 2010 the two surveys were carried out shortly after spring tide days and covered both the channel like south branch and the freshwater blocked north branch in the north branch with a water residence time of approximately one month we detected remarkable partial pressures of co 2 p co 2 of 930 1518 atm with a salinity range of 4 5 17 4 which were substantially higher than the south branch p co 2 values of 700 1100 atm at salinities of less than 0 88 the north branch p co 2 distribution pattern is unique compared with many other estuaries where aquatic p co 2 normally declines with salinity increase furthermore the biogeochemical additions of ammonium 7 4 65 7 mol kg 1 and alkalinity 196 695 mol kg 1 were identified in salinities between 4 and 16 in the north branch based on field data analyses and simplified stoichiometric equations we suggest that the relatively high north branch p co 2 values and estuarine additions of dissolved inorganic nitrogen carbon in the mid salinity area were strongly associated with each other these signals were primarily controlled by biogeochemical processes in the north branch combining biogenic organic matter decomposition i e respiration ammonia oxidation caco 3 dissolution and co 2 degassing in the upper reach of the south branch notable salinity values of 0 20 0 88 were detected indicating saltwater spillover from the north branch these spillover waters had minor contributions 1 5 6 9 to the springtime nutrient dissolved inorganic carbon and alkalinity export fluxes from changjiang to the adjacent east china sea this is the first attempt to understand the biogeochemical controls of the unique p co 2 distributions in the north branch and to evaluate the effects of saltwater spillover from the north branch on dry season export fluxes of biogenic elements to the adjacent east china sea

development of volcanic passive margins two dimensional laboratory models 1 continental breakup above an anomalously hot mantle may lead to the development of volcanic margins volcanic margins are characterized by 1 thick seaward dipping lava flow sequences 2 central intrusive complexes associated with dyke swarms parallel to the coast and 3 high seismic velocity bodies in the lower crust attributable to magma underplating a conceptual model for volcanic margins development has recently been proposed based on onshore studies of the greenland margins and the british tertiary igneous province it is proposed that the long lived central intrusions are genetically linked to underlying persistent zones of mantle fusion these localized melting domains or soft spots equivalent to small mantle diapirs may locally soften the extending continental lithosphere the low viscosity diapirs would 1 localize tectonic strain and 2 feed the volcanic margin with magma thus such soft spots can control the along strike magmatic and tectonic segmentation of volcanic margins recent geophysical investigations appear to show that the along strike structure of volcanic passive margins is compatible with such a segmentation process here we present a set of scaled experiments designed to study how such localized rheological heterogeneities in the sub moho mantle may have a mechanical effect on continental breakup four layer models were constructed using sand and silicone putties to represent the brittle and ductile layers of both crust and mantle the soft spots are simulated by low viscosity silicone putty emplaced within the brittle material at the scale of the entire breakup zone the soft spots display an oceanic type strength profile defining low strength zones where continental breakup is initiated the rift orientation and segmentation are strongly controlled by the distribution of the low viscosity heterogeneities rather than by the direction of regional extension the experiments are compared with the geometry and segmentation of the onshore part of the greenland volcanic margins

the effect of excess co2 on the calculated calcite and aragonite saturation horizons in the northeast pacific using the tco2 results of chen 1982a obtained during a cruise in the northeast pacific ocean june july 1981 we have calculated preindustrial and 1981 calcite and aragonite saturation horizons for a transect along 150 w between alaska and hawaii uptake of excess co2 by the oceans over the past 130 years has resulted in a significant change in the carbonate chemistry of the northeast pacific ocean the results indicate an apparent reduction in the thickness of the supersaturated lenses and an upward translation of the 100 saturation level by as much as 150 meters for calcite and 70 meters for aragonite in the coldwater region north of the subarctic front

continental rifting parallel to ancient collisional belts an effect of the mechanical anisotropy of the lithospheric mantle analysis of major rift systems suggests that the preexisting structure of the lithosphere is a key parameter in the rifting process rift propagation is not random but tends to follow the trend of the orogenic fabric of the plates systematically reactivating ancient lithospheric structures continental rifts often display a clear component of strike slip deformation in particular in the early rifting stage moreover although the close temporal and spatial association between flood basalt eruption and continental breakup suggests that mantle plumes play an important role in the rifting process there is a paradox between the pinpoint thermal and stress perturbation generated by an upwelling mantle plume and the planar geometry of rifts these observations suggest that the deformation of the lithosphere especially during rifting is controlled by its preexisting structure on the other hand 1 the plasticity anisotropy of olivine single crystal and aggregates 2 the strong crystallographic orientation of olivine observed in mantle xenoliths and lherzolite massifs and 3 seismic anisotropy data which require a tectonic fabric in the upper mantle coherent over large areas suggest that preservation within the lithospheric mantle of a lattice preferred orientation lpo of olivine crystals may induce a large scale mechanical anisotropy of the lithospheric mantle we use a polycrystal plasticity model to investigate the effect of a preexisting mantle fabric on the continental breakup process we assess the deformation of an anisotropic continental lithosphere in response to an axi symmetric tensional stress field produced by an upwelling mantle plume by calculating the deformation of textured olivine polycrystals representative of the lithospheric mantle at different positions above a plume head model results show that a lpo induced mechanical anisotropy of the lithospheric mantle may result in directional softening leading to heterogeneous deformation during continental rifting this mechanical anisotropy may induce strain localisation in domains where extensional stress is oblique 30 55 to the preexisting mantle fabric this directional softening associated with olivine lpo frozen in the lithospheric mantle may also guide the propagation of the initial instability that will follow the preexisting structural trend the preexisting mantle fabric also controls the deformation regime imposing a strong strike slip shear component a lpoinduced mechanical anisotropy may therefore explain the systematic reactivation of ancient collisional belts during rifting structural inheritance the plume rift paradox and the onset of transtension within continental rifts fl 2001 elsevier science b v all rights reserved

three dimensional gravity inversion for moho depth at rifted continental margins incorporating a lithosphere thermal gravity anomaly correction summary this paper describes a method for determining moho depth lithosphere thinning factor 1 1 and the location of the ocean continent transition at rifted continental margins using 3 d gravity inversion which includes a correction for the large negative lithosphere thermal gravity anomaly within continental margin lithosphere the lateral density changes caused by the elevated geotherm in thinned continental margin and adjacent ocean basin lithosphere produce a significant lithosphere thermal gravity anomaly which may be in excess of 100 mgal and for which a correction must be made in order to determine moho depth accurately from gravity inversion we describe a method of iteratively calculating the lithosphere thermal gravity anomaly using a lithosphere thermal model to give the present day temperature field from which we calculate the lithosphere thermal density and gravity anomalies for continental margin lithosphere the lithosphere thermal perturbation is calculated from the lithosphere thinning factor 1 1 obtained from crustal thinning determined by gravity inversion and breakup age for thermal re equilibration time for oceanic lithosphere the lithosphere thermal model used to predict the lithosphere thermal gravity anomaly may be conditioned using ocean isochrons from plate reconstruction models to provide the age and location of oceanic lithosphere a correction is made for crustal melt addition due to decompression melting during continental breakup and seafloor spreading we investigate the sensitivity of the lithosphere thermal gravity anomaly and the predicted moho depth from gravity inversion at continental rifted margins to the methods used to calculate and condition the lithosphere thermal model using both synthetic models and examples from the north atlantic

crustal structure and post rift evolution of the levant basin abstract petroleum exploration activity in the deep basins of the eastern mediterranean has been rejuvenated over the last decade with the discoveries of the giant tamar and leviathan gas fields made by noble energy and its partners and more recently with the discovery of the zohr field by eni with exploration efforts pursuing deeper and older leads a first principles quantitative study of the region seems timely while it is generally agreed that the levant basin formed along the northern passive margin of gondwanaland during the early mesozoic its complex post rift evolution has not been documented in detail located in a unique junction of three active tectonic plates and at the distal end of the nile one of the largest rivers on earth the levant basin is characterized by a thick sedimentary section more than half of which has accumulated since the oligocene in the last 15 of its existence this study implements a quantitative basin modelling workflow that assesses the three dimensional crustal geometry of the levant basin and its post rift evolution by integrating 3d gravity inversion and 3d flexural backstripping techniques the focus of the gravity inversion which includes corrections for the lithosphere thermal gravity anomaly resulting from lithosphere thinning and for the magmatic addition from decompression melting has been to predict both the 3d crustal structure and the magnitude of total lithospheric stretching for the levant basin the 3d flexural backstripping workflow using the outputs of the gravity inversion invokes three major processes in its calculations accompanying the layer by layer removal of the stratigraphy i 3d flexural isostatic unloading ii decompaction in response to the removal of overburden and iii reverse thermal subsidence modelling controlled by the stretching factor derived from the gravity inversion backstripping has produced a series of maps and cross sections depicting the evolution of post rift palaeobathymetry in the levant basin the integration of these techniques allows us to assess the evolution of the basin and the various sedimentary and tectonic events that have occurred since basin initiation although the calculated stretching factors indicate that while the lithosphere underlying the levant basin has been very highly stretched and thinned the stretching did not progress to the formation of new oceanic crust predicted palaeobathymetry portrays a thermally subsiding basin reaching maximum water depths at the onset of the cenozoic this deep basin provided ample amount of accommodation space for the large volumes of terrigenous clastics sourced from the contemporaneous uplift and exhumation of the basin margins and delivered in large part at least since the oligocene by the continental drainage of the nile these sediments have been filling and shallowing the basin ever since the basin evolution described here is consistent with available geophysical and geological data and has important implications for petroleum systems modelling within the basin

crustal structure of the southeastern brazilian margin campos basin from aeromagnetic data new kinematic constraints abstract the continental and adjacent marginal features along southeast brazil were investigated focusing on the basement structural relationships between onshore and offshore provinces lateral and vertical variations in the magnetic anomalies provided a good correlation with the regional tectonic features the sin rift dykes and faults are associated with the magnetic lineaments and lie sub parallel to the precambrian n45e s45w basement structure of the ribeira belt but orthogonally to the cabo frio tectonic domain cftd basement implying that 1 the upper portion of the continental crust was widely affected by mesozoic extensional deformation and 2 tectonic features related to the process of break up of the gondwana at the cftd were form regardless of the preexisting structural basement orientation being controlled by the stress orientation during the rift phase the deep crustal structure 5 km depth is characterized by ne sw magnetic provinces related to the ribeira belt tectonic units while deep suture zones are defined by magnetic lows the offshore campos structural framework is n30e s30w oriented and resulted from a main wnw ese direction of extension in early cretaceous transfer zones are represented by nw se and e w oriented discontinuities a slight difference in orientation between onshore n45e and offshore n30e structural systems seems to reflect a re orientation of stress during rifting we proposed a kinematical model to explain the structural evolution of this portion of the margin characterized by polyphase rifting associated with the rotation of the south american plate the campos magnetic high cmh an important tectonic feature of the campos basin corresponds to a wide area of high crustal magnetization the cmh wass interpreted as a magmatic feature mafic to ultramafic in composition that extends down to 14 km depth and constitutes an evidence of intense crustal extension at 60 km from the coast