ganges basin geometry records a pre 15 ma isostatic rebound of himalaya the tertiary continental strata of the himalayan foreland basin are subdivided into two groups but the meaning of this subdivision was previously unclear from the analysis of drill holes seismic lines dated sections outcrops and balanced cross sections we find that the southward migration rate of the depositional pinch out of the younger group is 19 5 mm yr and equals the himalayan shortening rate this equality shows that the flexural foreland basin development is mainly controlled by the motion of the thrust load the long term pinch out migration rate was slower for the older synorogenic group erosion locally occurred at the end of its deposition due to tectonic reactivation of lineaments of the indian shield we suggest that this change in the basin development is linked to the detachment of the subducted indian lithosphere that decreased the slab pull and increased the mean compressive stress within the indian plate whereas the plate motion remained constant the most important implication of our work is that the associated isostatic rebound could have increased the himalayan elevation prior to 15 ma

potential vorticity structure in the north atlantic western boundary current from underwater glider observations abstractpotential vorticity structure in two segments of the north atlantic s western boundary current is examined using concurrent high resolution measurements of hydrography and velocity from gliders spray gliders occupied 40 transects across the loop current in the gulf of mexico and 11 transects across the gulf stream downstream of cape hatteras cross stream distributions of the ertel potential vorticity and its components are calculated for each transect under the assumptions that all flow is in the direction of measured vertically averaged currents and that the flow is geostrophic mean cross stream distributions of hydrographic properties potential vorticity and alongstream velocity are calculated for both the loop current and the detached gulf stream in both depth and density coordinates differences between these mean transects highlight the downstream changes in western boundary current structure as the current increases its transport downstream upper layer potential vorticity is generall

surface changes in the eastern labrador sea around the onset of the little ice age despite the relative climate stability of the present interglacial it has been punctuated by several centennial time scale climatic oscillations the latest of which are often colloquially referred to as the medieval climatic anomaly mca and the little ice age lia the most favored explanation for the cause of these anomalies is that they were triggered by variability in solar irradiance and or volcanic activity and amplified by ocean atmosphere sea ice feedbacks as such changes in the strength of the atlantic meridional overturning circulation amoc are widely believed to have been involved in the amplification of such climatic oscillations the labrador sea is a key area of deep water formation the waters produced here contribute approximately one third of the volume transport of the deep limb of the amoc and drive changes in the north atlantic surface hydrography and subpolar gyre circulation in this study we present multi proxy reconstructions from a high resolution marine sediment core located south of greenland that suggest an increase in the influence of polar waters reaching the labrador sea close to mca lia transition changes in freshwater forcing may have reduced the formation of labrador sea water and contributed towards the onset of the lia cooling

the effects of a lateral variation in lithospheric strength on foredeep evolution implications for the east carpathian foredeep abstract lateral variations in lithospheric strength have been adopted often in flexural modeling both 2d and 3d to better fit the observed basement deflections typically supported by gravity data this approach provides essentially a snap shot of the role of lithosphere strength in determining the present day geometry in contrast we investigate and quantify the effects of a lateral change in lithospheric strength on the evolution of the foredeep in front of an advancing orogen transitions in lithospheric strength are common in the foreland of orogens and show large variations in the width of the transition zone and the strength difference former passive margins for instance will display strength changes distributed over several tens to hundreds of kilometers other transitions may originate from juxtaposition or accretion of pieces of lithosphere with different properties and may be characterized by a much smaller width than former passive margins in our modeling a constant load representing an advancing orogenic belt is displaced towards and across a transition from a weak to a strong plate in a 2d elastic thin plate model the effect of different transition widths and strength contrasts on foredeep geometry and bending stress is investigated interference of flexural wavelengths across the transition affects foredeep geometry by causing rapid basin widening oscillation of the bulge and volume increase the bending stresses are found to concentrate and amplify around the strength transition large transition gradients i e large strength contrast or small transition width cause the highest rates of change basin widening caused by the orogenic load advancing towards the transition between the east european craton and the moesian platform appears to control the sarmatian transgression over the east carpathian foreland in romania

fluid dynamics of oceanic thermocline ventilation abstract a flux form of the potential vorticity pv equation is applied to study the creation and transport of potential vorticity in an ocean gyre generalized pv fluxes j vectors and the associated pv flux fines are used to map the creation by buoyancy forcing of pv in the mixed layer and its transport as fluid is subducted through the base of the mixed layer into the thermocline the pv flux lines can either close on themselves recirculation or begin and end on the boundaries ventilation idealized thermocline solutions are diagnosed using j vectors which vividly illustrate the competing process of recirculation through western boundary currants and subduction from the surface potential vorticity flux vectors are then used to quantify the flux of mass passing invisidly through a surface across which potential vorticity changes discontinuously but at which potential density and velocity are continuous such a surface might be the base of the oceanic mixed layer or in a meteorological context

mapping ocean observations in a dynamical framework a 2004 06 ocean atlas abstract this paper exploits a new observational atlas for the near global ocean for the best observed 3 yr period from december 2003 through november 2006 the atlas consists of mapped observations and derived quantities together they form a full representation of the ocean state and its seasonal cycle the mapped observations are primarily altimeter data satellite sst and argo profiles gcm interpolation is used to synthesize these datasets and the resulting atlas is a fairly close fit to each one of them for observed quantities especially the atlas is a practical means to evaluate free running gcm simulations and to put field experiments into a broader context the atlas derived quantities include the middepth dynamic topography as well as ocean fluxes of heat and salt freshwater the atlas is publicly available online www ecco group org this paper provides insight into two oceanographic problems that are the subject of vigorous ongoing research first regarding ocean circulation estimates

friction frontogenesis and the stratification of the surface mixed layer the generation and destruction of stratification in the surface mixed layer of the ocean is understood to result from vertical turbulent transport of buoyancy and momentum driven by air sea fluxes and stresses in this paper it is shown that the magnitude and penetration of vertical fluxes are strongly modified by horizontal gradients in buoyancy and momentum a classic example is the strong restratification resulting from frontogenesis in regions of confluent flow frictional forces acting on a baroclinic current either imposed externally by a wind stress or caused by the spindown of the current itself also modify the stratification by driving ekman flows that differentially advect density ekman flow induced during spindown always tends to restratify the fluid while wind driven ekman currents will restratify or destratify the mixed layer if the wind stress has a component up or down front i e directed against or with the geostrophic shear respectively scalings are constructed for the relative importance of friction versus frontogenesis in the restratification of the mixed layer and are tested using numerical experiments of mixed layer fronts forced by both winds and a strain field the scalings suggest and the numerical experiments confirm that for wind stress magnitudes mixed layer depths and cross front density gradients typical of the ocean wind induced friction often dominates frontogenesis in the modification of the stratification of the upper ocean the experiments reveal that wind induced destratification is weaker in magnitude than restratification because the stratification generated by up front winds confines the turbulent stress to a depth shallower than the ekman layer which enhances the frictional force ekman flow and differential advection of density frictional destratification is further reduced over restratification because the stress associated with the geostrophic shear at the surface tends to compensate a down front wind stress

the north atlantic eddy heat transport and its relation with the vertical tilting of the gulf stream axis correlations between temperature and velocity fluctuations are a significant contribution to the north atlantic meridional heat transport especially at the northern boundary of the subtropical gyre in satellite observations and in a numerical model at 1 12 resolution a localized pattern of positive eddy heat flux is found northwest of the gulf stream downstream of its separation at cape hatteras it is confined to the upper 500 m a simple kinematic model of a meandering jet can explain the surface eddy flux taking into account a spatial shift between the maximum velocity of the jet and the maximum cross jet temperature gradient in the gulf stream such a spatial shift results from the nonlinear temperature profile and the vertical tilting of the velocity profile with depth the numerical model suggests that the meandering of the gulf stream could account at least in part for the large eddy heat transport of order 0 3 pw near 36 n in the north atlantic and for its compensation by the mean flow

multi scale depositional successions in tectonic settings observations in sedimentary basins affected by deformation show that the fault induced depositional accommodation at various spatial and temporal scales is closely linked to basin kinematics the tectonically driven sediment infill displays the history of deepening and shoaling facies that are controlled by the activation of faults and changes in their offset rates simply stated this results in shifting sedimentary facies towards the source area or towards the basin centre in response to increasing or decreasing depositional space we propose a first principle conceptual model for tectonic successions controlled by the balance between the rates of creation of depositional space and sediment supply these sediment bodies are bounded by succession boundaries and comprise sourceward or basinward shifting facies tracts that are separated at a point of reversal due to the relatively steep slopes associated with the evolution of faults changes in sediment supply rates and mass wasting are common in these systems and may complicate the normal rhythm of the shifting facies tracts once tectonic quiescence is achieved and if the basin is connected to the open ocean eurybatic or eustatic base level changes may take over and play a greater role in sedimentary rhythm and cyclicity we illustrate the efficacy of the new concept with a review of examples from extensional contractional and strike slip basins we show that the basic tectonic succession model is applicable at all temporal and spatial scales and whether the tectonics cause subsidence or uplift and in all types of tectonic settings that determine the evolution of sedimentary basins

permian to late triassic evolution of the longmen shan foreland basin western sichuan model results from both the lithospheric extension and flexure abstract the lithosphere was extended during the permian middle triassic in the yangtze craton where the sichuan basin located and then bent due to thrusting of the longmen shan orogen leading to formation of the longmen shan foreland basin western sichuan during the late triassic indosinian orogeny the lateral variation of the lithospheric strength resulted by former differential extension would inevitably influence the subsequent evolution of the foreland basin in order to investigate this both extensional and flexural models were applied in modeling permian late triassic basin evolution a 2d kinematic extensional model was initially developed along a profile crossing the yangtze craton to simulate the lithospheric thermal evolution during the permian middle triassic based on the thermal results the thermal rheological structure as well as the effective elastic thickness of the lithosphere te was then determined extension model show that the stretching factors decrease gradually from songpan ganzi to the sichuan basin leading to variable thermal rheological structure and increased te from west to east taking into account of the te variation a flexural model was finally constructed to investigate the evolution of the longmen shan foreland basin during the late triassic spanning the time period c 227 206 ma three episodes were divided according to the corresponding tectonostratigraphic units by matching the stratigraphic observations three phase advance distances eastward of the longmen shan along the qingchuan maowen fault turned out to be 18 22 and 18 km it implied a slow and similar thrust advance rate of 3 6 c 227 222 ma 2 2 c 222 212 ma and 3 mm yr c 212 206 ma respectively

diagnosing the observed seasonal cycle of atlantic subtropical mode water using potential vorticity and its attendant theorems analyzed fields of ocean circulation and the flux form of the potential vorticity equation are used to map the creation and subsequentcirculation of lowpotential vorticity waters known as subtropical mode water stmw in the north atlantic novel mapping techniques are applied to i render the seasonal cycle and annual mean mixed layer vertical flux of potential vorticity pv through outcrops and ii visualize the extraction ofpv from the mode water layer in winter over and to the south of the gulf stream both buoyancy loss and wind forcing contributetotheextractionofpv buttheauthorsfindthattheformergreatlyexceedsthelatter thesubsequent path of stmw is also mapped using bernoulli contours on isopycnal surfaces

influence of the north atlantic sst on the atmospheric circulation using the monthly coads dataset and nmc ncar archives we show that significant anomalies of the atmospheric circulation are related to previous sst anomalies in the north atlantic a signal over the northwest labrador sea in late spring is associated with the dominant mode of sst variability during the preceeding winter it is more clearly seen in the mid troposhere than at sea level and appears to be related to the anomalous surface heat exchanges that slowly damp the sst anomalies in addition a nao like signal in early winter is associated with sst anomalies east of newfoundland and in the eastern subtropical north atlantic during the preceeding summer

effects of the submesoscale on the potential vorticity budget of ocean mode waters abstractnonconservative processes change the potential vorticity pv of the upper ocean and later through the subduction of surface waters into the interior affect the general ocean circulation

perspectives on the ethiopian volcanic province published major element analyses of ethiopian volcanic rocks have been subjected to a systematic discriminant analysis the plateau regions can be subdivided according to the proportions of alkaline and tholeiitic basalts in northern ethiopia these subprovinces show increasing basalt alkalinity with time the most voluminous basalts have lowest magnesium values independent of the degree of alkalinity rift and afar basalt chemistry falls within the spectrum observed for the plateau basalts with no perceptible difference resulting from lithospheric attenuation beneath afar however silicic volcanics of the rift afar floor differ in bulk terms from those of the plateau margins in showing a stronger bias towards peralkalinity and having higher na k values two particularly voluminous volcanic episodes have occurred in ethiopia dated at 30 19 m y and 4 5 0 m y and which link well with one model for seafloor spreading in the red sea and gulf of aden evidence for a mantle hotspot under ethiopia remains ambiguous

robustness of low frequency circulation patterns derived from eof and rotated eof analyses abstract the robustness of low frequency circulation patterns defined by unrotated and rotated empirical orthogonal functions e0fs are compared based on the northern hemisphere 10 day low pass filtered wintertime 500 hpa height field the pacific north american pattern and the north atlantic oscillation are the most prominent modes of low frequency variability in the data the reproducibility of the spatial patterns derived from eof and rotated eof analysis is assessed by repeating the analysis on 50 subsets of the data each comprised of the maps belonging to 22 randomly selected winters from the 44 winters in the total record the results indicate that rotated spatial patterns are less sensitive to sampling fluctuations than their unrotated counterparts

effects of ekman transport on the nao response to a tropical atlantic sst anomaly abstract a recent study showed that a tropical atlantic sea surface temperature sst anomaly induces a significant coupled response in late winter february april fma in a coupled model in which an atmospheric general circulation model is coupled to a slab mixed layer ocean model agcm ml the coupled response comprises a dipole in the geopotential height like the north atlantic oscillation nao and a north atlantic tripole in the sst the simulated nao response developed 1 or 2 months later in the model than in observations to determine the possible effects of ekman heat transport on the development of the coupled response to the tropical forcing an extended coupled model agcm eml including ekman transport in the slab mixed layer ocean is now used large ensembles of agcm eml experiments are performed parallel to the previous agcm ml experiments with the model forced by the same tropical atlantic sst anomaly over the boreal winter months september april the inclusion of ekman heat tra

geographical variability of the first baroclinic rossby radius of deformation global 1 83 18 climatologies of the first baroclinic gravity wave phase speed c1 and the rossby radius of deformation l1 are computed from climatological average temperature and salinity profiles these new atlases are compared with previously published 5 83 58 coarse resolution maps of l1 for the northern hemisphere and the south atlantic and with a 1 83 18 fine resolution map of c1 for the tropical pacific it is concluded that the methods used in these earlier estimates yield values that are biased systematically low by 5 15 owing to seemingly minor computational errors geographical variations in the new high resolution maps of c1 and l1 are discussed in terms of a wkb approximation that elucidates the effects of earth rotation stratification and water depth on these quantities it is shown that the effects of temporal variations of the stratification can be neglected in the estimation of c1 and l1 at any particular location in the world ocean this is rationalized from consideration of the wkb approximation

on multidecadal and quasi decadal north atlantic variability observed sea surface temperatures ssts in the north atlantic from 1958 through 2000 as well as data from an ocean model simulation driven with the atmospheric variability observed during the same period are examined using multichannel singular spectrum analysis the two leading oscillatory modes are associated with a multidecadal and a quasi decadal period the former is connected to a basinwide uniform sst pattern and changes in the deep north atlantic meridional overturning circulation the quasi decadal mode involves a tripolar sst anomaly pattern forced by atmospheric variability with a spatial structure resembling that of the north atlantic oscillation nao the upper ocean s dynamical response to this nao variability provides an instantaneous positive feedback to the sst pattern while a delayed negative feedback is due to shallow overturning circulation anomalies

role of the gulf stream and kuroshio oyashio systems in large scale atmosphere ocean interaction a review abstract ocean atmosphere interaction over the northern hemisphere western boundary current wbc regions i e the gulf stream kuroshio oyashio and their extensions is reviewed with an emphasis on their role in basin scale climate variability sst anomalies exhibit considerable variance on interannual to decadal time scales in these regions low frequency sst variability is primarily driven by basin scale wind stress curl variability via the oceanic rossby wave adjustment of the gyre scale circulation that modulates the latitude and strength of the wbc related oceanic fronts rectification of the variability by mesoscale eddies reemergence of the anomalies from the preceding winter and tropical remote forcing also play important roles in driving and maintaining the low frequency variability in these regions in the gulf stream region interaction with the deep western boundary current also likely influences the low frequency variability surface heat fluxes damp the low frequency sst anomalies ove

extratropical atmospheric response to equatorial atlantic cold tongue anomalies abstract the extratropical atmospheric response to the equatorial cold tongue mode in the atlantic ocean has been investigated with the coupled ocean atmosphere model speedy ocean speedo similar to the observations the model simulates a lagged covariability between the equatorial cold tongue mode during late boreal summer and the east atlantic pattern a few months later in early winter the equatorial cold tongue mode attains its maximum amplitude during late boreal summer however only a few months later when the itcz has moved southward it is able to induce a significant upper tropospheric divergence that is able to force a rossby wave response the lagged covariability is therefore the result of the persistence of the cold tongue anomaly and a favorable tropical atmospheric circulation a few months later the rossby wave energy is trapped in the south asian subtropical jet and propagates circumglobally before it reaches the north atlantic due to the local increase of the hadley circulation fo

discrimination of local and global effects on upper mississippian stratigraphy illinois basin u s a abstract interpretive cross sections based on detailed descriptions of 33 outcrops and cores are used to better understand the relative effects of tectonics eustasy tides and climate on upper mississippian middle chesterian stratigraphy in the tectonically active tide dominated illinois basin the cross sections show that five mixed carbonate siliciclastic high frequency sequences in the bethel through glen dean formations can be correlated around the outcrop belt through areas with very different subsidence histories the sequence boundaries are marked by paleosols and incised valleys and can be correlated basin wide within a framework of distinctive marker beds because of its updip position lowstand systems tracts are not preserved in the illinois basin the transgressive systems tracts generally consist of one or two parasequences that are typically composed of tidally influenced quartz sandstone filling incised valleys at the base overlain by open marine skeletal limestone shallow marine shale and heterolithic siliciclastic tidal flat deposits the maximum flooding surface mfs for the sequences is picked at the base of the deepest water limestone facies highstand systems tracts are composed of 1 to 6 regressive parasequences that consist of basal offshore skeletal limestone capped by laterally extensive shale and heterolithic siliciclastic tidal flat facies the basin wide extent of the sequence boundaries and maximum flooding surfaces across tectonic highs and lows suggests that the sequences were produced by eustatic sea level changes rather than local tectonics or autogenic processes the sequences were likely produced by moderate to high amplitude 30 100 m fourth order 400 ky glacio eustatic sea level changes driven by the transition from the greenhouse conditions of the early mississippian to the icehouse conditions of the late paleozoic the lateral extent and frequency of component parasequences suggests that they were likely produced by fifth order sea level changes 10 100 ky the sequences may be bundled into third order composite sequences but the third order signal is obscured by the magnitude of the fourth order sea level changes a feature typical of ice house stratigraphies the sequences can be used as time slices to identify spatial and temporal variations in differential subsidence between the cincinnati arch and the more rapidly subsiding basin interior episodes of high and low differential subsidence occurred every two to three sequences these subsidence variations had a major impact on lithofacies distribution and onlap and offlap geometries in sequences and parasequences the occurrence of some widespread seismically disturbed beds suggests that active faulting occurred during deposition normal faulting appears to have occurred during periods of high differential subsidence and reverse faulting during periods of low differential subsidence differential subsidence and related normal and reverse faulting may have occurred in response to phases of thrust loading and quiescence in the appalachian orogenic belt to the east even in this tectonically active setting however it is the eustatic signal that generates basin wide mappable stratigraphic sequences

local and remote impacts of a tropical atlantic salinity anomaly the climatic impacts of an enhanced evaporation prescribed during 50 years in the tropical atlantic are investigated in a coupled ocean atmosphere general circulation model locally the salinity increase leads to a rapid deepening and cooling of the surface mixed layer this induces a deepening of the equatorial undercurrent and an intensification of the south equatorial current a remote atmospheric response to the tropical atlantic perturbation is detected in the north atlantic sector after ten years it has the form of a robust wave like tropospheric perturbation seemingly excited by the weakening of atmospheric deep convection over the amazonian basin meanwhile the salt anomaly is carried northward by the mean oceanic circulation it is traced up to the convection sites and then on its return path at depth towards lower latitudes consistent with the density increase deep convection is enhanced after the arrival of the salt anomaly and the atlantic meridional overturning circulation amoc intensifies about 20 years after the beginning of the perturbation the adjustment of the tropical atlantic to the amoc intensification then modifies its initial response to the freshwater forcing leading to a weaker cooling in the northern tropical atlantic than in the southern tropical atlantic a slight northward shift of the tropical atlantic precipitation pattern and an intensification of the north brazil current on the other hand no significant anomalous precipitations are found in the pacific the initial remote atmospheric response is also modulated by an nao like response to the amoc intensification

parameterization of mixed layer eddies part i theory and diagnosis ageostrophic baroclinic instabilities develop within the surface mixed layer of the ocean at horizontal fronts and efficiently restratify the upper ocean in this paper a parameterization for the restratification driven by finite amplitude baroclinic instabilities of the mixed layer is proposed in terms of an overturning streamfunction that tilts isopycnals from the vertical to the horizontal the streamfunction is proportional to the product of the horizontal density gradient the mixed layer depth squared and the inertial period hence restratification proceeds faster at strong fronts in deep mixed layers with a weak latitude dependence in this paper the parameterization is theoretically motivated confirmed to perform well for a wide range of mixed layer depths rotation rates and vertical and horizontal stratifications it is shown to be superior to alternative extant parameterizations of baroclinic instability for the problem of mixed layer restratification two companion papers discuss the numerical implementation and the climate impacts of this parameterization

late cenozoic burial history and dynamics of the northern caucasus molasse basin implications for foreland basin modelling abstract the collisional history of the caucasus segment of the alpine himalayan fold belt started at the end of the eocene the associated development of the northern caucasus foreland basin occurred during two syn collisional stages each displaying different subsidence patterns the 34 16 ma maikopian or pre foreland stage displays a long wavelength subsidence of a broad area whereas the 16 0 ma foreland stage displays asymmetrical foreland subsidence the first is correlated with the termination of subduction in the southern area and can be associated with mantle flow induced by the re equilibration of the subducted slab the along strike configuration of the second molasse basin stage contradicts the hypothesis in which topographical loading is considered to be the main control on foreland subsidence there is a clear anti correlation between basin depths and orogen heights the deepest parts of the basin are at the tips of the orogen where mountain heights are negligible while the area adjacent to the highest mountains central caucasus is uplifted the influence of other types of loading in foreland basin development has therefore been investigated and it has been possible to find a good fit with both gravity and basin architecture by including only two additional model parameters into the model these are crustal and lithospheric thickening thinning the results demonstrate that crustal thickening and removal of lithospheric roots are responsible for supporting the high central caucasus mountains and uplift of adjacent areas the subsidence of the basins at the orogen tips is explained by loading of lithospheric roots both effects are important in the geographically intermediate areas in general it is concluded that topography should not be considered as the main control on foreland subsidence but only as one of several counterbalancing mechanisms the existing flexural model therefore needs improvements such that it can be related directly to subsurface loading by real structures and processes during collision

modelling of piggyback basin stratigraphy record of tectonic evolution abstract the tectono stratigraphic evolution of foreland basins is influenced by processes acting on local regional and global scale in this paper the effects of these processes on the basin evolution are investigated using a forward reconstruction model based on the principles of balanced cross section the modelling incorporates the consequences of thrust deformation sedimentation erosion basement subsidence and sealevel changes on the basin stratigraphy basement subsidence due to lithospheric loading is the main cause of foreland basin formation but appears to have minor implications for the occurrence of angular unconformities in the stratigraphie record of piggyback basins thrusting is probably the dominant factor in the control of the stratigraphie evolution of piggyback basins overprinting the effect of eustasy detailed analyses of stratigraphie data enable the reconstruction of the structural evolution of the underlying thrust system modelling of the northern apenninic po basin shows that neogene stratigraphie sequences of the proximal part of the basin can be explained by tectonic activity of the apenninic fold and thrust belt strong basement subsidence accompanied with deep seated mid pliocene thrusting controls the stratigraphie record of the po piggyback basins

destruction of potential vorticity by winds the destruction of potential vorticity pv at ocean fronts by wind stress driven frictional forces is examined using pv flux formalism and numerical simulations when a front is forced by downfront winds that is winds blowing in the direction of the frontal jet a nonadvective frictional pv flux that is upward at the sea surface is induced the flux extracts pv out of the ocean leading to the formation of a boundary layer thicker than the ekman layer with nearly zero pv and nonzero stratification the pv reduction is not only active in the ekman layer but is transmitted through the boundary layer via secondary circulations that exchange low pv from the ekman layer with high pv from the pycnocline extraction of pv from the pycnocline by the secondary circulations results in an upward advective pv flux at the base of the boundary layer that scales with the surface nonadvective frictional pv flux and that leads to the deepening of the layer at fronts forced by both downfront winds and a destabilizing atmospheric buoyancy flux f b the critical parameter that determines whether the wind or the buoyancy flux is the dominant cause for pv

volume and potential vorticity budgets of eighteen degree water abstractmode waters are a distinctive baroclinic feature of the world ocean characterized by relatively weak vertical stratification they correspond dynamically to low potential vorticity pv in the north atlantic subtropical gyre the mode waters have become known as eighteen degree water their dynamics involves air sea interaction diapycnal and isopycnal mixing and subduction understanding mode water dynamics is therefore both challenging and important since it connects several aspects of the ocean circulation mass and pv budget of the mode water s core evaluated in a realistic primitive equation north atlantic model are used to characterize mode water maintenance it is shown that the surface pv flux has very little impact on mode water the surface buoyancy flux in combination with eddy mass flux is the most important control on mode water structure a mean pv formalism is used to show that the pv and water mass formation budgets are intrinsically linked a decomposition of the budget demons

basalt geochemistry and tectonic discrimination within continental flood basalt provinces abstract continental flood basalts are usually regarded as a single tectonomagmatic entity but frequently quoted examples exhibit a variety of tectonic settings in one well studied classic flood basalt province the mesozoic karoo province of southern africa magmatism occurred in the following tectonic settings a continental rifting leading to ocean floor spreading in the south atlantic ocean etendeka suite of namibia b stretched continental lithosphere and rifting not leading directly to ocean floor formation lebombo suite of southeastern africa and c an a tectonic within plate continental setting characterized by an absence of faulting or warping lesotho highlands and karoo dolerites of south africa by means of spidergrams of the elements rb ba th nb k la ce sr nd p hf zr sm ti tb y v ni and cr uncontaminated tholeiites from c above i e the lesotho type continental flood basalts ltcfb are compared with mid ocean ridge basalts morb ocean island tholeiites oit and tholeiites and calc alkali basalts from subduction environments the comparison reveals the ltcfbs are geochemically distinct the differences are reflected in relative enrichments or depletions of the more incompatible elements rb ce to less incompatible elements ce y i e the overall slope of the spidergrams and in anomalous enrichments or depletions of one or more of the elements th k nb sr ti hf and zr the distinctive geochemical character of the lesotho ltcfbs is interpreted in terms of a lithospheric mantle source for the basalts this is supported by isotopic data there are no major geochemical differences between lesotho cfbs and basalts of the rift related etendeka and lebombo suites although the latter are somewhat enriched in rb ba and k however unlike the lesotho basalts the lebombo and etendeka basalts are associated with voluminous silicic volcanics or intrusive centres and late stage dolerites having morb oit i e asthenospheric geochemical characteristics the flood basalt silicic magmatism late stage dyke swarm association is characteristic of several rift or thinned lithosphere environments e g ethiopia skye eastern greenland but in many of these the flood basalts have ocean island basalt oit geochemical characteristics the lesotho type cfb geochemistry is exhibited by the grande ronde basalt of the columbia river group a possible subduction related flood basalt province and the basic rocks associated with mesozoic rifting in the north and south atlantic basalt geochemistry alone is unhelpful in determining the tectonic setting of cfbs although the rift related environments may be identified by the petrology and geochemistry of the whole igneous suite a two source model is proposed for the mantle derived basic rocks in rift related cfb provinces early enriched basalts are derived from the lithosphere and following pronounced lithospheric attenuation or rifting later morb like melts are emplaced from the rising asthenosphere the presence of both lesotho and oit type geochemical patterns in rift related cfbs suggests that the lithosphere exhibits different styles of enrichment

tectonic controls on the genesis and distribution of late cretaceous western interior basin hydrocarbon seep mounds tepee buttes of north america abstract within the western interior basin of north america hundreds of small carbonate mounds associated with late cretaceous hydrocarbon emissions or seeps form the most extensively distributed occurrence of fossil seep mounds that is known the tepee buttes analysis of the stratigraphic literature for the basin reveals that tepee butte formation occurred intermittently over a 10 m yr period within a narrowly restricted paleogeographic region the modern geographic distribution of the tepee buttes is constrained roughly to between 101 30 documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empt

observed impact of atlantic sst anomalies on the north atlantic oscillation the large scale patterns of covariability between monthly sea surface temperature sst and 500 mb height anomalies z500 in the atlantic sector are investigated as a function of time lag in the ncep ncar reanalysis 1958 97 in agreement with previous studies the dominant signal is the atmospheric forcing of sst anomalies but statistically significant covariances are also found when sst leads z500 by several months in winter a panatlantic sst pattern precedes the north atlantic oscillation nao by up to 6 months such long lead time covariance is interpreted in the framework of the stochastic climate model reflecting the forcing of the nao by persistent atlantic sst anomalies a separate analysis of midlatitudes 208 708n and tropical 208s 208n sst anomalies reveals that the bulk of the nao signal comes from the midlatitudes a dipolar anomaly with warm sst southeast of newfoundland and cold sst to the northeast and southeast precedes a positive phase of the nao and it should provide a prediction of up to 15 of its monthly variance several months in advance since the forcing sst pattern projects significantly onto the tripole pattern generated by the nao these results indicate a positive feedback between the sst tripole and the nao with a strength of up to 25 mk 21 at 500 mb or 2 3 mb k21 at sea level additionally a warming of the tropical atlantic 208s 208n roughly symmetric about the equator induces a negative nao phase in early winter this tropical forcing of the nao is nearly uncorrelated with and weaker than that resulting from the midlatitudes and is associated with shorter lead times and reduced predictive skill

basement reactivation in a sub andean foreland flexural bulge the pantanal wetland sw brazil the role of sub andean foreland peripheral bulges in controlling sedimentary sequence deposition and quaternary geomorphology is discussed in the case of the pantanal wetland sw brazil this shallow 0 5 km and wide 200 km depression was formed because of uplift and flexural extension in the brittle upper crust which mechanically reactivated the neoproterozoic paraguai fold thrust belt depth to the basement and structural information within the pantanal wetland were obtained from gravity reflection seismics drill hole and digital topography data the upper part of the basin is filled with pliocene quaternary unlithified sands the age of the oldest sediments is unknown and normal faults are mostly observed on the western border of the basin a two dimensional flexural model composed of a semi infinite thin elastic plate for the brazilian shield lithosphere with an effective elastic thickness of 125 150 km its western edge at 67 5 w under the altiplano and loaded on a free end by the andes topography predicts the forebulge to be presently located over the pantanal wetland flexural modeling was constrained using gravity data extending from the pacific ocean to the east of the pantanal wetland the width of the bulge is 700 km and its amplitude is 310 m the total amount of extension and subsidence observed in the pantanal basin is interpreted as due to a cumulative strain since late oligocene when the brazilian shield started its westward migration together with compression and uplift of the central andes the main phase of the wetland subsidence is very likely related to the last compressional pulse in the andes during the upper pliocene lower pleistocene 2 5 ma as inferred from field study of fault kinematics of the central andes

submesoscale instabilities in mesoscale eddies submesoscale processes have been extensively studied in observations and simulations of fronts recent idealized simulations show that submesoscale instabilities also occur in baroclinic mesoscale cyclones and anticyclones the instabilities in the anticyclone grow faster and at coarser grid resolution than in the cyclone the instabilities lead to larger restratification in the anticyclone than in the cyclone the instabilities also lead to changes in the mean azimuthal jet around the anticyclone from 2 km resolution but a similar effect only occurs in the cyclone at 0 25 km resolution a numerical passive tracer experiment shows that submesoscale instabilities lead to deeper subduction in the interior of anticyclonic than cyclonic eddies because of outcropping isopycnals extending deeper into the thermocline in anticyclones an energetic analysis suggests that both vertical shear production and vertical buoyancy fluxes are important in anticyclones but primarily vertical buoyancy fluxes occur in cyclones at these resolutions the energy sources and sinks vary azimuthally around the eddies caused by the asymmetric effects of the ekman buoyancy flux glider transects of a mesoscale anticyclone in the tasman sea show that water with low stratification and high oxygen concentrations is found in an anticyclone in a manner that may be consistent with the model predictions for submesoscale subduction in mesoscale eddies

thick skin orogen foreland interactions and their controlling factors northern andes of colombia the study draws from reflection seismic in situ stress and low temperature geochronology data on the eastern cordillera llanos foreland basin system of colombia which is an example of the retro wedge of the orogen with an advancing subduction zone the system was obliquely converging during deposition of the lower oligocene lower miocene carbonera to recent guayabo formations recording it by the northeastward depocentre shift in the proximal llanos basin while the southern portion of the foreland did not flex and undergo flexural normal faulting after carbonera deposition the northern portion did the earthquake data indicate that the northern eastern cordillera undergoes strengthening by internal deformation while the southern segment is already strong enough to undergo significant displacements dominantly along its bounding fault systems furthermore the southern segment initiated detachment of the first thick skin blocks from the proximal llanos basin such co existence of different convergence maturity stages along the orogen strike allows unravelling of its development starting with internal deformation and foreland flexure followed by mountain building and large scale boundary fault displacements to the large scale foreland deformation the onset of new foreland accretion seems to be controlled by the resistance of the foreland plate to flexing given that the orogenic engine continues to drive convergence

surface vertical pv fluxes and subtropical mode water formation in an eddy resolving numerical simulation abstract subtropical mode waters are characterized by low potential vorticity pv and so the mechanisms by which pv is extracted from the ocean by air sea interaction are of great relevance to our understanding of how mode waters are formed this study analyzes those mechanisms by comparing the magnitude and spatial patterns of surface pv fluxes of diabatic and frictional origin in a high resolution numerical simulation of the north atlantic the model resolves mesoscale eddies and exhibits realism in the volume and regional distribution of subtropical mode water both in the annual mean and seasonal cycle it is found that the diabatic and mechanic fluxes of pv through the sea surface are of similar amplitude locally but their spatial structures are very different the diabatic pv flux has a large scale pattern that reflects that of air sea heat fluxes directed from the ocean to the atmosphere along and to the south of the separated gulf stream in contrast the mechanical pv flux because of its dependence on horizontal surface density gradients exhibits much smaller scales but embedded within a coherent large scale pattern when mapped over the north atlantic subtropical mode water edw outcropping region the diabatic pv flux pattern is found to be directed out of the ocean everywhere whereas the mechanical pv fluxes exhibits small scale patterns of both sign the amplitude of the diabatic pv fluxes is found to be at least one order of magnitude larger than the mechanical pv fluxes demonstrating the overwhelming importance of diabatic processes in creating mode waters finally we note that the large scale climatological patterns and magnitudes of both diabatic and mechanical pv flux mapped over the edw outcropping region are very similar to patterns obtained from coarse grained ocean state estimates that do not resolve the eddy field

influence of the north atlantic sst variability on the atmospheric circulation during the twentieth century the ocean atmosphere coupling in the north atlantic is investigated during the twentieth century using maximum covariance analysis of sea surface temperature sst and 500 hpa geopotential height analyses and performing regressions on dynamical diagnostics such as eady growth rate wave activity flux and velocity potential the north atlantic oscillation nao generates the so called sst anomaly tripole a rather similar sst anomaly tripole with the subpolar anomaly displaced to the east and a more contracted subtropical anomaly which is referred to as the north atlantic horseshoe pattern in turn influences the atmosphere in the fall and early winter the response is nao like and primarily results from subpolar forcing centered over the labrador sea and off newfoundland in summer the largest atmospheric response to sst resembles the east atlantic pattern and results from a combination of subpolar and tropical forcing to emphasize the interannual to multidecadal variability the same analysis is repeated after low pass filtering the sst influence is dominated by the atlantic multidecadal oscillation amo which also has a horseshoe shape but with larger amplitude in the subpolar basin a warm amo phase leads to an atmospheric warming limited to the lower troposphere in summer while it leads to a negative phase of the nao in winter the winter influence of the amo is suggested to be primarily forced by the atlantic ssts in the northern sub tropics such influence of the amo is found in winter instead of early winter because the winter sst anomalies have a larger persistence presumably because of sst reemergence

observed atlantic sst anomaly impact on the nao an update abstract the pan atlantic sea surface temperature sst anomaly pattern that was found in a previous study to have a significant impact on the north atlantic oscillation nao in early winter seemed to reflect the nearly uncorrelated influence of a horseshoe sst anomaly in the north atlantic and an sst anomaly in the eastern equatorial atlantic a lagged rotated maximum covariance analysis of a slightly longer dataset shows that the horseshoe sst anomaly influence is robust but it deemphasizes the center of action southeast of newfoundland canada on the other hand it suggests that the link between equatorial sst and the nao was artificial and due both to enso teleconnections and the orthogonality constraint in the maximum covariance analysis

mixed layer instabilities and restratification abstract the restratification of the oceanic surface mixed layer that results from lateral gradients in the surface density field is studied the lateral gradients are shown to be unstable to ageostrophic baroclinic instabilities and slump from the horizontal to the vertical these instabilities which are referred to as mixed layer instabilities mlis differ from instabilities in the ocean interior because of the weak surface stratification spatial scales are o 1 10 km and growth time scales are on the order of a day linear stability analysis and fully nonlinear simulations are used to study mlis and their impact on mixed layer restratification the main result is that mlis are a leading order process in the ml heat budget acting to constantly restratify the surface ocean climate and regional ocean models do not resolve the scales associated with mlis and are likely to underestimate the rate of ml restratification and consequently suffer from a bias in sea surface temperatures and ml depths in a

basaltic volcanism in the northern sector of the main ethiopian rift abstract the different basalt types related to rift structure development have been investigated starting from the pre rift stage in the northern ethiopian rift and its eastern escarpment and plateau the basic volcanic rocks are represented mainly by transitional basalts both in the pre rift plateau and rift escarpment and rift floor stages a striking feature is that although the plateau basalts show clear tholeiitic affinity and the rift basalts reveal a somewhat pronounced alkaline character the ree and lile element abundances however progressively decrease from the tholeiitic basalts of the plateau to the alkaline basalts of the rift all data support the view that such contrasting features may be attributed to a continuous depletion of hygromagmatophile ree lile elements in the mantle source material related to the large volumes of magmas produced in the early phase of rift structure development the transition from tholeiitic plateau to alkaline rift transitional basalts is related to decreasing intensity of extensional movements

effects of the mixed layer time variability on kinematic subduction rate diagnostics abstract an eddy resolving primitive equation general circulation model is used to estimate water mass subduction rates in the north atlantic ocean subtropical gyre the diagnostics are based on the instantaneous kinematic approach which allows the calculation of the annual rate of water mass subduction at a given density range following isopycnal outcrop positions over the annual cycle it is shown that water mass subduction is effected rapidly 1 2 months as the mixed layer depth decreases in spring consistent with stommel s hypothesis and occurs mostly over the area of deep late winter mixed layers 150 m across the central north atlantic in the density range 26 27 2 annual subduction rates o 100 200 m yr 1 are found south and east of the gulf stream extension in the density range of subtropical mode waters from roughly 26 2 to 26 6 in the northeastern part of the subtropical gyre annual subduction rates are somewhat larger o 250 m yr 1 from a density of about 26 9 east of the nort

carbonate platform drowning in a foreland setting the mid carboniferous platform in western urals russia abstract the stratigraphic evolution through time of the mid carboniferous russian platform deposited on the distal margin of the west uralian prograding foredeep basin can be observed in the approximately 3000 m thick sedimentary cover that constitutes the upper paleozoic foreland mid carboniferous permian of the uralian fold belt it is composed of wave dominated low angle carbonate ramps of late visean to early moscovian age and carbonate platforms bordered by slope reef mounds from the kasimovian to the late artinskian early kungurian eastward in the foredeep the carbonate platforms pass into terrigenous deposits a complete transgressive progradational section at the transition between carbonate ramp and terrigenous deposits exhibits from base to top 1 deepening upward carbonate ramp deposits 2 a shaly condensed section with volcaniclastics glauconite and phosphorites of late moscovian to early asselian age the transgressive part and 3 a shallowing upward section of turbidites ending in coarse grained fan deltas evaporites and meandering river redbeds by the earliest triassic the progradational section this paper focuses on the uppermost part of the carbonate ramp deposits serpukhovian to early moscovian these ramp facies comprise peritidal channels and mud flats wave to storm dominated shoals and patch reefs that are overlain by channel attached sand lobes of turbidites black shales and radiolarites of the condensed section this large scale deepening upward trend from inner ramp to outer ramp environments reflects a change in the depositional profile from a tide and wave dominated flat ramp to a wave and storm dominated steepened ramp margin and then to foreslope turbidites correlation of sections dated by fusulinid faunas in southern urals shows that the ramp evolved from emergent in the north perm solikamsk area as evidenced by karstification and deepened to the south belaya area with emplacement of carbonaceous foreslope debris flows and turbidites capped by deep marine black shales and radiolarites the time gap increases northward and reaches a span including the siuransky pro parte the akavassky the askynbashky and the asatausky pro parte biohorizons the mapping of these facies belts across all the urals shows that carbonate ramps wedge out in the middle urals and give rise to widely distributed diversified and deeper marine facies belts not only to the south towards the precaspian depression but also to the north towards the polar urals the drowning of these carbonate ramps and the cutoff in carbonate production on the russian platform during the mid carboniferous is explained by a succession of low frequency flexure relaxation cycles in the foreland associated with dilution by siliciclastics outpouring of volcaniclastics and changes in the nature and direction of the sediment input and high frequency cycles mainly controlled by eustasy

north atlantic ocean surface currents 1 close to 1800 surface drifters are used to investigate the 15 m circulation of the north atlantic ocean the data are used to describe structures of the average eulerian circulation and of the associated eddy variability the data resolve scales on the order of 50 km which have hitherto not been systematically described in particular near shelf breaks and near the most intense currents the gulf stream the north atlantic current nac and the frontal currents of the subpolar gyre this reveals a complex series of quasi permanent eddies meanders and recirculation patterns gulf stream intensity is portrayed as changing abruptly near 54 w east of which it is identified as two current branches centered near 39 and 41 5 n the northern one connecting more directly with the nac and the southern one with the recirculation gyre and the azores current ac many features of the currents are controlled by topography in particular currents are often intensified near shelf breaks or parallel to ridges in the subpolar gyre however the largest northward branch of the nac in the icelandic basin is located near the deepest bathymetry not near steep bathymetry other currents in particular in the subtropical gyre are less clearly related to topography for instance the ac is featured as a zonal eastward current extending far west of the mid atlantic ridge mar to at least 55 w and possibly 63 w in the interior and away from topographic features the eddy kinetic energy eke is the largest where the mean currents are the largest in the subpolar gyre there are striking differences in eke between southward flowing currents the labrador and east greenland current and the northward flowing currents west greenland current and branches of the nac which have higher eke the areas of weakest variability are located in the southwest part of the subpolar gyre northeast of iceland and in the eastern atlantic south of 45 n the ac eddies and the mesoscales south of the canary islands transect this eastern eddy desert drifter trajectories are used as realizations of lagrangian particles in the vicinity of current cores these illustrate the variety of paths or connections between different current systems and demonstrate cross stream dispersions

on the structure and teleconnections of north atlantic decadal variability abstractdecadal variability in the north atlantic has been associated in the literature with a tripolar pattern of sea surface temperature sst anomalies that show one sign in the western midlatitudinal north atlantic and the opposite in the subpolar and tropical north atlantic the present analysis of observed sst from 1870 to 2009 leads to the dissection of the sst tripole into two components each with a different time scale in the decadal band and different teleconnections in the atlantic basin while the subpolar and tropical poles present quasi decadal variations with a period of about 9 years essentially uncorrelated with other parts of the basin the center of action in the western midlatitudes is characterized by a longer time scale of about 14 years and significant correlations with the tropical south atlantic and the norwegian and north sea s the 9 yr period variations are associated with an atmospheric configuration resembling the east atlantic pattern whereas the 14 yr period fluctuation

decadal windstorm activity in the north atlantic european sector and its relationship to the meridional overturning circulation in an ensemble of simulations with a coupled climate model the relationship between decadal variations in the north atlantic meridional overturning circulation moc and north atlantic western european windstorm activity during the extended winter season is studied according to an ensemble of three 240 year long simulations performed with the echam5 mpiom model periods of high decadal windstorm activity frequently occur in the years following a phase of weak moc i e when the moc starts to recover these periods are characterised by a distinctive pattern in the mixed layer ocean heat content ohc a positive anomaly is located in the region 45 n 52 n 35 w 16 w west of france negative anomalies are located to the north and south the signal can be detected both in the heat content of the oceanic mixed layer and in the sea surface temperatures its structure is consistent with anomalously enhanced baroclinic instability in the region with the strong negative ohc gradient 30 w 10 w 45 n 60 n which eventually produces a higher probability of windstorms

subsidence analysis in thrust tectonics application to the southeastern pyrenean foreland abstract this case study conducted in the pyrenees examines the application of 1d subsidence analysis in thrust tectonics by integrating subsidence analysis with sequence stratigraphy and structure significant changes between the subsidence curves of the southeastern pyrenean thrust sheets are seen to occur bearing a close relationship to regional unconformities and variations in the sedimentary record of each thrust sheet a comparative study examining the correlation between the tectonic subsidence curves of the thrust sheets and those of the autochthon shows that the essential structure of the southward sequence of thrust sheets palaeozoic axial zone not included was piggy back developed in only 6 m y the northern garrotxa antiformal stacks started to emplace 50 7 ma ago as can be interpreted from their linear shaped curve and anomalously low subsidence rate 7 cm ka and preservation of continental platform whereas the southern cadi thrust sheet underwent strong subsidence acceleration up to 60 cm ky related to the development of a deep starved continental slope comparison between coeval platform sections with good palaeobathymetric constraints and slope sections provides an estimate for slope palaeobathymetry up to 650 900 m the cadi thrust sheet was emplaced at about 49 5 ma as can be deduced from dramatic subsidence deceleration in its curves related to shallowing resumption of siliciclastic sedimentation and broad erosion of the continental platform areas of the cadi thrust sheet meanwhile the curves of the serrat thrust sheet and those of the autochthon recorded significant subsidence acceleration 30 40 cm ka and 15 cm ka respectively finally the serrat thrust sheet was emplaced at 45 ma as can be inferred from the decelerated subsidence in its curve associated with shallowing emergence and broad molasse sedimentation whereas in the foreland plate the subsidence accelerated and was related to the onset of marine sedimentation

entry flux and exit of potential vorticity in ocean circulation the flux form of the potential vorticity pv equation is employed to derive simple expressions for the boundary and interior flux of pv in ocean circulation using bernoulli functions the formulas are discussed and physically interpreted and used to map the flux of pv through a model of ocean circulation

symmetric instability in the gulf stream abstract analyses of wintertime surveys of the gulf stream gs conducted as part of the clivar mode water dynamic experiment climode reveal that water with negative potential vorticity pv is commonly found within the surface boundary layer sbl of the current the lowest values of pv are found within the north wall of the gs on the isopycnal layer occupied by eighteen degree water suggesting that processes within the gs may contribute to the formation of this low pv water mass in spite of large heat loss the generation of negative pv was primarily attributable to cross front advection of dense water over light by ekman flow driven by winds with a down front component beneath a critical depth the sbl was stably stratified yet the pv remained negative due to the strong baroclinicity of the current suggesting that the flow was symmetrically unstable a large eddy simulation configured with forcing and flow parameters based on the observations confirms that the observed structure of the sbl is consistent with the dynamics of symmetric instability si forced by wind and surface cooling the simulation shows that both strong turbulence and vertical gradients in density momentum and tracers coexist in the sbl of symmetrically unstable fronts si is a shear instability that draws its energy from geostrophic flows a parameterization for the rate of kinetic energy ke extraction by si applied to the observations suggests that si could result in a net dissipation of 33 mw m 2 and 1 mw m 2 for surveys with strong and weak fronts respectively the surveys also showed signs of baroclinic instability bci in the sbl namely thermally direct vertical circulations that advect biomass and pv the vertical circulation was inferred using the omega equation and used to estimate the rate of release of available potential energy ape by bci the rate of ape release was found to be comparable in magnitude to the net dissipation associated with si this result points to an energy pathway where the gs s reservoir of ape is drained by bci converted to ke and then dissipated by si and its secondary instabilities similar dynamics are likely to be found at other strong fronts forced by winds and or cooling and could play an important role in the energy balance of the ocean circulation

a base level stratigraphic approach to determining holocene subsidence of the ganges meghna brahmaputra delta plain abstract relative sea level history which is the result of the combined effects of land subsidence sediment supply and absolute sea level history may be reconstructed from preserved sediment thicknesses however variations in the preserved sediment thicknesses between different sedimentary environments strongly limit the accuracy of this type of geological approach particularly in fluvial channelized systems such as delta plains to address this we apply three different and independent stratigraphic approaches to the case of the ganges brahmaputra meghna delta gbmd our approach has been made possible by a broad dataset of geological archives we have collected which includes more than 400 hand drilled stratigraphic wells 198 radiocarbon ages and river seismic reflection data 255 km of high resolution multichannel seismic images the seaward gradient of accommodation and the limit of the subsiding delta plain are estimated assuming that the delta is near or at the base level which is considered to be the relative sea level first a statistical analysis of the variability of preserved sediment thicknesses is used to derive the average pattern of accommodation from the holocene isopach secondly the preserved sediment thicknesses are analyzed by geomorphotectonic domains to estimate an average pattern of accommodation thirdly the burial history of the seismically imaged last glacial incision of the brahmaputra river is reconstructed results suggest that the variability of preserved sediment thicknesses can be up to 35 in a delta plain between river channel and flood plain deposits for the same relative sea level history taking this variability into consideration the holocene relative sea level history of the gbmd and the most likely pattern of subsidence are determined results provide evidence of moderate holocene subsidence over the delta gently increasing seaward from

the gulf of aden structure and evolution of a young ocean basin and continental margin new marine geophysical data are used to describe the structure and history of the gulf of aden magnetic anomaly data shows seafloor spreading magnetic anomalies of sheba ridge from the axial anomaly to anomaly 5 10 m y b p between the owen fracture zone and 45 sup 0 e and to anomaly 2 3 m y b p or anomaly 3 4 m y b p west of 45 sup 0 e the data does not support the two episodes of seafloor spreading recently proposed landward of the seafloor spreading magnetic anomalies is a magnetic quiet zone of uncorrelatable anomalies the magnetic quiet zone boundary is also a structural boundary effectively marking the edge of sheba ridge with deeper basement lacking a significant topographic gradient found on the landward side a magnetic quiet zone is found not only where sheba ridge splits continental lithosphere but also on east sheba ridge where the ridge splits the old oceanic lithosphre of the owen and somali basins there the position occupied by the continental margin within the gulf is marked by nonmagnetic ridge complexes that stretch from the continents to the owen fracture zone the magnetic quiet zone boundary is not an isochron in either the gulf of aden ormore the red sea suggesting that significant horizontal motions can occur prior to the initiation of seafloor spreading the offset on the dead sea rift is used to estimate that from 80 to 160 km of opening amounting to between 65 and 200 extension of the initial rift valley occurred in the gulf of aden and red sea prior to the establishment of a mid ocean ridge it is suggested that the development of a new ocean basin occurs in two stages the first involves diffuse extension over an area perhaps 10 km wide in a rift valley environment without an organized spreading center this is followed by concentration of the extension at a single axis and the beginning of true seafloor spreading less

new age constraints on the timing of volcanism and tectonism in the northern main ethiopian rift southern afar transition zone ethiopia abstract forty new k ar and 40 ar 39 ar isotopic ages from the northern main ethiopian rift mer southern afar transition zone provide insights into the volcano tectonic evolution of this portion of the east african rift system the earliest evidence of volcanic activity in this region is manifest as 24 23 ma pre rift flood basalts transition zone flood basalt activity renewed at approximately 10 ma and preceded the initiation of modern rift margin development bimodal basalt rhyolite volcanism in the southern afar rift floor began at approximately 7 ma and continued into recent times in contrast post subsidence volcanic activity in the northern mer is dominated by mio pliocene silicic products from centers now covered by quaternary volcanic and sedimentary lithologies unlike other parts of the mer mio pliocene silicic volcanism in the mer afar transition zone is closely associated with fissural basaltic products the presence of pliocene age ignimbrites on the plateaus bounding the northern mer whose sources are found in the present rift indicates that subsidence of this region was gradual and that it attained its present physiography with steep escarpments only in the plio pleistocene large 7 5 ma silicic centers along the southern afar and northeastern mer margins apparently formed along an e w oriented regional structural feature parallel to the already established southern escarpment of the afar the addis ababa rift embayment and the growth of 4 5 3 ma silicic centers in the addis ababa area are attributed to the formation of a major cross rift structure and its intersection with the same regional e w structural trend this study illustrates the episodic nature of rift development and volcanic activity in the mer afar transition zone and the link between this activity and regional structural and tectonic features

does enso force the pna abstract the primary effect of el nino southern oscillation enso sea surface temperature sst anomalies is to force distinct midlatitude patterns and not only to modify the probability of the internal variability patterns such as the pacific north american pna pattern of wallace and gutzler both the spatial structure and probability distribution of the external enso pattern are distinct from the pna pattern ensemble general circulation model gcm integrations for 30 winters have been analyzed in the pacific north america region these winters span the recent period of 1981 82 through 1998 99 plus 12 earlier winters the entire dataset includes six el nino warm and seven la nina cold events the ensemble size is nine simulations empirical orthogonal function eof analysis is carried out for all gcms and observed seasonal means for the gcm ensemble means and for the gcm deviations about the ensemble means eof 1 of the gcm 200 hpa height z ensemble mean agrees well with eof 1 of all gc

role of the tropical atlantic sea surface temperature in the decadal change of the summer north atlantic oscillation 1 recent observational studies have shown that the southern center of the summer north atlantic oscillation snao shifted eastward after the late 1970s in this study this phenomenon and its causes are further explored it is found that the decadal spatial shift of the snao southern center is related to the decadal variability of the tropical atlantic sea surface temperature tasst in the past half century the tasst experienced an abrupt change around the late 1970s with a rapid warming in the recent 2 decades thus in the period after the late 1970s when the tasst is relatively warmer the tasst released more energy into the atmosphere then stimulated strong convection over the tropical atlantic and further excited anomalous wave like patterns this strengthened the circulation in the region of the mediterranean sea namely the east part of the snao southern center consequently leading to an eastward shift of the snao southern center meanwhile in the period before the late 1970s when the tasst is relatively cooler the tasst released less energy into the atmosphere so its impact on the overlying atmosphere was significantly weakened and confined to the lower level atmosphere of the tropical atlantic thus the tasst possibly did not influence the variability of the snao southern center and the snao pattern exhibited a traditional distribution with two centers over the north atlantic

episodicity in foredeep basins the stratigraphic record contained in several foredeep basins is incompatible with the formation of these basins by flexure of a homogeneously strong foreland lithosphere for example the stratigraphy of the early proterozoic kilohigok foredeep basin of northern canada indicates that the inner part of the basin deepened in time without migration of the flexural bulge toward the foreland and that the flexural bulge remained fixed in time relative to the downgoing plate one mechanism that may be responsible for the localization of the flexural bulge in the kilohigok and similar basins is that of lateral strength variations in the flexing lithosphere our results show that lateral strength variations within the foreland lithosphere can produce temporal variations in basin geometry and also serve to localize the position of the flexural bulge relative to the foreland for extended periods of time this produces basin episodicity on a time scale of millions to tens of millions of years perfectly elastic models require a large strength contrast about 50 in elastic plate thickness but a brittle elastic ductile lithosphere rheology reduces the magnitude of the strength contrast required for episodicity to about 10 15 of the initial effective elastic plate thickness we suggest that basin episodicity may induce comparable episodicity in the coeval thrust belt because theoretical studies of thrust mechanics suggest that the deformation in thrust belts is highly sensitive to the dip of the basal thrust angle through mechanisms such as this the laterally heterogeneous continental lithosphere may provide a natural filter that transforms the presumably continuous and smoothly varying processes of the mantle into the spatially irregular and temporally episodic deformation observed in the crust at time scales of tens of millions of years

year to year reoutcropping of eighteen degree water in an eddy resolving ocean simulation abstractwinter outcropping of the eighteen degree water edw and its subsequent dispersion are studied using a eddy resolving simulation of the family of linked atlantic modeling experiments flame outcropped edw columns in the model simulations are detected in each winter from 1990 to 1999 and particles are deployed in the center of each outcropped edw column subsequently the trajectories of these particles are calculated for the following 5 yr the particles slowly spread away from the outcropping region into the nonoutcropping subducted edw region south of 30 n and eventually to the non edw region in the greater subtropical gyre approximately 30 of the particles are found in non edw waters 1 yr after deployment after 5 yr only 25 of the particles are found within edw the reoutcropping time is defined as the number of years between when a particle is originally deployed in an outcropping edw column and when that particle is next found in an outcropping edw column of the particles 66 ar

the contributions of atmosphere and ocean to north atlantic subtropical mode water volume anomalies abstract subtropical mode water stmw in the western north atlantic ocean or eighteen degree water edw as it is commonly known is formed near the gulf stream in the wintertime is dissipated by mixing and is removed by subduction the ability of edw to store and discharge large quantities of heat over periods of several years contributes to the memory of the climate system to complement the 2 year field and modeling program of the clivar mode water dynamics experiment climode with a perspective of interannual to decadal variability 1985 2007 we used a simple box model to hindcast observed edw volume anomalies in two regions one in which edw is formed and an adjacent region of subducted edw estimates of the relative contributions of heat flux anomalies vertical mixing from ekman advection mixing and circulation are examined using proxy variables derived from winds sea surface temperature hydrographic data and altimetric sea level the importance of each process is evaluated by its contribution to observed edw volume anomalies in two regions the study produced some robust conclusions 1 anomalies of formation by surface heat fluxes are clearly reflected in edw volume anomalies with some contributions by ekman advection 2 of the newly formed edw about 65 is lost by mixing and about 35 is transferred to the subducted region 3 mixing losses are well parameterized by the meandering of the nearby gs and 4 transfer and losses from the subducted region can be parameterized by the geostrophic surface flow

direct observation of subtropical mode water circulation in the western north atlantic ocean abstract eighteen degree water edw is the dominant subtropical mode water of the north atlantic subtropical gyre and is hypothesized as an interannual reservoir of anomalous heat nutrients and co2 although isolated beneath the stratified upper ocean at the end of each winter edw may re emerge in subsequent years to influence mixed layer properties and consequently air sea interaction and primary productivity here we report on recent quasi lagrangian measurements of edw circulation and stratification in the western subtropical gyre using an array of acoustically tracked isotherm following bobbing profiling floats programmed to track and intensively sample the vertically homogenized edw layer and directly measure velocity on the 18 5 c isothermal surface the majority of the clivar mode water dynamics experiment climode bobbers drifted within the subtropical gyre for 2 5 3 5 years many exhibiting complex looping patterns indicative of an energetic eddy field bobber derived lagrangian integral time and length scales 3 days 68 km associated with motion on 18 5 c were consistent with previous measurements in the gulf stream extension region and fall between previous estimates at the ocean surface and thermocline depth several bobbers provided evidence of long lived submesoscale coherent vortices associated with substantial edw thickness while the relative importance of such vortices remains to be determined our observations indicate that these features can have a profound effect on edw distribution edw thickness defined using a vertical temperature gradient criterion exhibits seasonal changes in opposition to a layer bounded by the 17 c and 19 c isotherms in particular edw thickness is generally greatest in winter as a result of buoyancy forced convection while the 17 19 c layer is thickest in summer consistent with seasonal ekman pumping contrary to previous hypotheses the bobber data suggest that a substantial fraction of subducted edw is isolated from the atmosphere for periods of less than 24 months seasonal to biennial re emergence principally within the recirculation region south of the gulf stream appears to be a common scenario which should be considered when assessing the climatic and biogeochemical consequences of edw

observations of entry and exit of potential vorticity at the sea surface abstract although potential vorticity pv is central to many theories of the oceanic circulation the entry exit of pv at the sea surface has not been thoroughly discussed from an observational perspective after clarifying the notion of pv entry and exit and the mechanisms responsible for it a climatology of this quantity for the northern hemisphere is presented it is found that surface pv loss over western boundary current regions and their interior extension is a robust feature over the north pacific and atlantic basins at high latitudes mechanical and diabatic effects act in concert in the north atlantic to drive the net pv exit in the pacific however these effects oppose each other and the net entry exit of pv is more uncertain at low latitudes surface winds are found to be particularly important in setting the surface pv exit in the pacific equatorward of the intertropical convergence zone

extratropical atmospheric response to the atlantic nino decaying phase abstract the atlantic nino or atlantic equatorial mode em is the dominant coupled variability phenomenon in the tropical atlantic basin during boreal summer from the 1970s the mode has changed evolving in time from east to west and without persisting until the following winter in a previous observational work the authors have studied the atmospheric response to the em during the 1979 2005 period proposing three main issues along the decaying phase of this mode 1 the continuous confinement of the anomalous deep convection over northeastern brazil following the thermal forcing decay 2 an increasing dipole like precipitation anomaly with dry conditions in the florida gulf of mexico region and 3 the excitation of rossby waves forced by the remaining upper tropospheric divergence that are trapped into the subtropical jet but do not show a robust impact on the european sector in this work a 10 member ensemble simulation for the recent em with the university of california los angeles agcm model

subduction on the northern and southern flanks of the gulf stream abstract sections of temperature salinity dissolved oxygen and velocity were made crossing the gulf stream in late january 2006 to investigate the role of frontal processes in the formation of eighteen degree water edw the subtropical mode water of the north atlantic the sections were nominally perpendicular to the stream and measured in a lagrangian frame by following a floating spar buoy drifting in the gulf stream s warm core during the survey edw was isolated from the mixed layer by the stratified seasonal pycnocline suggesting that edw was not yet actively being formed at this time in the season and at the longitudes over which the survey was conducted 64 70 w however in two of the sections the seasonal pycnocline in the core of the gulf stream was broken by an intrusion of cold fresh weakly stratified water nearly saturated in oxygen that appears to have been subducted from the surface mixed layer north of the stream the intrusion was identified in three of the sections in profi

interpreting provenance relations from sandstone detrital modes southern italy foreland region stratigraphic record of the miocene tectonic evolution abstract the southern italy orogen preserves deep marine turbitic clastic wedges that record the key tectonic events during structural growing over the adria margin the regional tectonic transition from thick skinned calabrian accretion and deformation during late paleogene to middle miocene to thin skinned southern apennines thrusting since early middle miocene is recorded by diverse contrasting petrofacies in uppermost paleogene and miocene sandstones of dominantly turbiditie deposits most of these sandstones reflect in time quartzolithic and quartzofeldspathic and arkosic petrofacies derived from growing and unroofing calabrian terranes quartzose petrofacies mainly indicate provenance from cratonal african margin during langhian and or from lowland internal domains before its deformation during the cretaceous to paleogene volcaniclastic sandstone petrofacies also testify active volcanism during the late paleogene to early miocene these variable compositions indicate strong palaeogeographic constraints for the central western mediterranean during the neogene reflecting provenance relationships from differentiate source rocks these include interplays between ophiolitiferous uplifted continental shallow to deep crust terranes volcanic and sedimentary mostly carbonate source rocks sandstone detrital modes provide an example of the close relations between clastic compositions and growing orogen in southern italy and may contribute to unravel the geodynamic history of other major orogens

observed decadal tropical pacific north atlantic teleconnections 1 observations of the last century are considered to investigate the decadal scale pacific north atlantic teleconnections by using wavelet analysis we find a significant low frequency coherency between major indices of climate variability in particular at periods between 10 and 20 yr the north atlantic oscillation nao tends to be out of phase with the el nino southern oscillation enso strong icelandic low during la nina and the pacific decadal oscillation pdo but in phase with the north pacific index npi hence the icelandic low is strong during la nina but the aleutian low is weak the band pass sst pattern shows a close relationship between the decadal enso mode in the pacific and the sea surface temperature anomaly tripole in the atlantic consistent with the low frequency global teleconnections the spatial sea level patterns corresponding to the band pass filtered indices suggest that the aleutian icelandic low seesaw is a main interbasin link on decadal time scale consistent with the larger coherency of the npi with the nao than with enso

buoyancy and wind driven convection at mixed layer density fronts in this study the influence of a geostrophically balanced horizontal density gradient on turbulent convection in the ocean is examined using numerical simulations and a theoretical scaling analysis starting with uniform horizontal and vertical buoyancy gradients convection is driven by imposing a heat loss or a destabilizing wind stress at the upper boundary and a turbulent layer soon develops for weak lateral fronts turbulent convection results in a nearly homogeneous mixed layer ml whose depth grows in time for strong fronts a turbulent layer develops but this layer is not an ml in the traditional sense because it is characterized by persistent horizontal and vertical gradients in density the turbulent layer is however nearly homogeneous in potential vorticity pv with a value near zero using the pv budget a scaling for the depth of the turbulent low pv layer and its time dependence is derived that compares well with numerical simulations two dynamical regimes are identified in a convective layer near the surface turbulence is generated by the buoyancy loss at the surface below this layer turbulence is generated by a symmetric instability of the lateral density gradient this work extends classical scalings for the depth of turbulent boundary layers to account for the ubiquitous presence of lateral density gradients in the ocean the new results indicate that a lateral density gradient in addition to the surface forcing can affect the stratification and the rate of growth of the surface boundary layer

neogene to quaternary sedimentary basins in the south adriatic central mediterranean foredeeps and lithospheric buckling up to several kilometers deep sedimentary basins of neogene to quaternary age are found in the south adriatic between the apennines and the dinarides albanides they are the apennines foredeep the central adriatic basin and the south adriatic basin two regional seismic lines 260 and 170 km long across the entire system provide hitherto unavailable constraints on the kinematics and dynamics of basin development the apennine foredeep imaged along the lines formed in middle to late pliocene times through a rapid westward tilting of the basin floor a paleobathymetry of few kilometers was created in which allochthonous bodies were emplaced and sediments deposited unaffected by deformation and farther rotations the central and south adriatic basins formed in neogene to quaternary times and are both characterized by strong subsidence in their central parts gradually diminishing toward the edges in the sw and ne depocenters did not shift laterally through time subsidence rates increase through time and subsidence continued also following the end of main shortening episodes in the dinarides albanides the central and south adriatic basins form two crustal scale synclines with subsidence concentrated in their central parts basins geometries and subsidence patterns indicate that the adriatic crust has undergone episodes of buckling since miocene times wavelengths and amplitudes of such folds change along strike corresponding to mechanical changes of the folded medium