residual mean solutions for the antarctic circumpolar current and its associated overturning circulation abstract residual mean theory is applied to the streamwise averaged antarctic circumpolar current to arrive at a concise description of the processes that set up its stratification and meridional overturning circulation on an f plane simple solutions are found in which transfer by geostrophic eddies colludes with applied winds and buoyancy fluxes to determine the depth and stratification of the thermocline and the pattern of associated residual meridional overturning circulation

partitioning of kinetic energy in the arctic ocean s beaufort gyre kinetic energy ke in the arctic ocean s beaufort gyre is dominated by the mesoscale eddy field that plays a central role in the transport of freshwater heat and biogeochemical tracers understanding beaufort gyre ke variability sheds light on how this freshwater reservoir responds to wind forcing and sea ice and ocean changes the evolution and fate of mesoscale eddies relate to energy pathways in the ocean e g the exchange of energy between barotropic and baroclinic modes mooring measurements of horizontal velocities in the beaufort gyre are analyzed to partition ke into barotropic and baroclinic modes and explore their evolution we find that a significant fraction of water column ke is in the barotropic and the first two baroclinic modes we explain this energy partitioning by quantifying the energy transfer coefficients between the vertical modes using the quasi geostrophic potential vorticity conservation equations with a specific background stratification observed in the beaufort gyre we find that the quasi geostrophic vertical mode interactions uphold the persistence of ke in the first two baroclinic modes consistent with observations our results explain the specific role of halocline structure on ke evolution in the gyre and suggest depressed transfer to the barotropic mode this limits the capacity for frictional dissipation at the sea floor and suggests that energy dissipation via sea ice ocean drag may be prominent

the arcs of the western alps and the northern apennines an updated view abstract the arcs of the western alps and the northern apennines and the link between them are in the process of being investigated using the european geotraverse and they have historically been interpreted in many different ways new information particularly geophysical further constrains possible models both arcs have evolved in several stages sometimes complexly interrelated and sometimes independent of each other compressional belts produced in these stages have either been of the push arc type indentation into a deformable mass or the pull arc type backward migration of hinge of a subduction zone leading to small extensional basins known as back arc basins and pores with an arcuate mountain range on the subduction side extensional periods with the possible formation of pull arcs in the alps comprise the gosau period between the eo and meso alpine push arc phases and the oligocene lull period between the meso and the neo alpine push arc phases in the northern apennines remainders of the meso alpine nappes were involved in oligocene early miocene pull arc formation associated with spreading in the balearic sea followed by push arc formation particularly in the middle miocene and by renewed pull arc formation from the latest late miocene to the present during all of these developments the moho was modified by such processes as lithospheric stretching asthenospheric intrusions subhorizontal shearing and isostatic uplift the present moho configuration is consequently a collage of moho patches formed at different intervals both push and pull arcs are laterally bounded by complementary strike slip or transform zones these too were modified in the course of history and their final geometry is consequently of a very complex nature in the alps for instance the insubric fault zone appears to have been the main dextral transform fault of the neogene push arc until it was sinistrally kinked by the giudicarie fault zone and probably deactivated dextral transpression being briefly transferred to the en echelon brachyanticlines of the late alpine windows in the case of the oligocene apennines the sinistral rotations of corsica and sardinia otherwise hard to understand may be attributed in part to sinistral transform motions along the eastern border zone of the oligocene early miocene balearic extension

the maritime alps arc in the ligurian and tyrrhenian systems abstract after late eocene meso alpine collision between the european and adria plates the maritime alps underwent further deformations linked to the apennine orogenesis and consistent with a stress field developed during anticlockwise rotation the western limit of the rotated sector is east of the argentera massif and to the southwest represents the northwestern margin of the post eocene ligurian sphenochasm the sinistral rotation of the maritime alps initially occurred contemporaneous with the opening of the ligurian basin about 30 19 ma and probably continued during the subsequent opening of the tyrrhenian basin about 10 0 ma the rotating block comprises the northwestern part of the adria indenter and a part of the paleo european plate namely the maritime alps corsica and sardinia if a convenient configuration is assumed for the moho of the adria margin and suitable poles are chosen for subsequent rotations then a simplified model of rigid body can explain the rotation structures in the maritime alps the apennines and po plain subsurface compressional arcs the late foreland directed transport of nappes in the western alps the presence of extensional and dextral transcurrent structures and the general uplift of the lithospheric mantle between the ligurian sea and the ivrea body as to the causes of rotation two alternatives subduction or asthenosphere uplift are discussed chronological and mechanical arguments seem to favour the latter

cooling and uplift patterns in the lepontine alps south central switzerland and an age of vertical movement on the insubric fault line 96 new fission track ft apatite and zircon k ar and rb sr biotite and muscovite ages are presented for 19 samples mainly acid gneisses from a 40 km traverse through the lepontine alps in the maggia valley south central switzerland plotting measured mineral ages against assumed system closure temperatures yields cooling rates for each sample the entire profile shows a fairly uniform late neogene recent mean uplift rate of 0 5 mm a confirmed by a gradient of ft apatite age with elevation cooling from higher temperatures occurred earlier in the south where uplift rates of 2 2 mm a in the steep belt root zone indicate 9 km early miocene uplift of the northern pennine block this uplift started before 23 ma and is interpreted as resulting from a major phase of backthrusting along the insubric line and as dating the formation of the mylonite belt estimated cooling rates constrain the timing of lepontine mid tertiary metamorphism 3 schematic models are proposed which also consider published rb sr k ar mica and hornblende and u pb monazite ages slow cooling differential initial heating and subsequent cooling of different parts of the central alps and post 38 ma cooling with syntectonic metamorphism at 27 ma are postulated as alternative interpretations of isotopic data and geologic evidence from extrapolation between k ar and rb sr mica ages and apatite ft ages 240 50 c is proposed as the closure temperature for the retention of fission tracks in zircon

on the interplay between the circulation in the surface and the intermediate layers of the arctic ocean abstractthe circulation of the arctic ocean has traditionally been studied as a two layer system with a wind driven anticyclonic gyre in the surface layer and a cyclonic boundary current in the atlantic water aw layer primarily forced remotely through inflow and outflow to the basin here an idealized numerical model is used to investigate the interplay between the dynamics of the two layers and to explore the response of the circulation in each of the layers to a change in the forcing in either layer in the model the intensity of the circulation in the surface and aw layers is primarily set by the ocean surface stress curl intensity and the inflow to the basin respectively additionally the surface layer circulation can strongly modulate the intensity of the intermediate layer by constraining the lateral extent of the aw current on the slope in contrast a change in the aw current strength has little effect on the surface layer circulation the intensity of the circulation in the surface layer

oligo miocene rift of sardinia and the early history of the western mediterranean basin the geodynamic evolution of the western mediterranean basin in spite of many studies is still uncertain there is some consensus for interpreting this basin as a kind of small oceanic marginal basin its opening has generally been related to a subduction process which was active during the oligocene miocene somewhere east of sardinia corsica1 7 as the margins of the basin are deeply buried below miocene to present sediments direct lithological and stratigraphical data which could explain the events responsible for its formation are rare8 10 or missing altogether to obtain such data detailed field studies have been undertaken in sardinia fig 1 and the first results are presented here this approach is justified by the fact that in that island oligocene and miocene sediments were deposited in a rift fossa tettonica sarda of verdabasso11 which is the easternmost arm of the complex rift system that affected the european plate during oligocene and miocene times one of these arms evolved towards a small oceanic basin the western mediterranean or algero provencal basin while others such as the gulf of valencia and the sardinia rift aborted and remained at the rift stage its exceptional exposures make it possible to examine the sardinia rift to clarify the sequence of events which created it and to establish a sedimentological model which we believe is directly applicable to the western mediterranean basin

dating of deformation phases using k ar and 40ar 39ar techniques results from the northern apennines abstract paleozoic to oligocene metasedimentary rocks present in the alpi apuane region of the northern apennines italy have been sequentially deformed during a tertiary progressive deformation in an attempt to date the individual deformation episodes over 50 conventional k ar and 1140 ar 39ar incremental gas release analyses have been carried out on fine grained white micas separated from samples whose structural settings were well known mineralogy x ray diffractometry and thin section analyses indicate that the constituent muscovite and phengite formed under metamorphic conditions of 3 4 kbars and 300 400 c during all deformational phases pre existing micas were variably crenulated during each subsequent deformational phase both k ar and 40ar 39ar analyses were carried out on 0 6 2 m 2 6 m and 6 20 m size separates of the phengitic white mica although the k ar apparent ages range from 11 to 27 ma and are consistent with available stratigraphic constraints the 40ar 39ar age spectra display variable internal discordancy these isotopic data indicate that 1 both the k ar and 40ar 39ar total gas ages decrease as the degree of crenulation increases 2 the k ar and 40ar 39ar total gas ages decrease as grain size decreases 3 for each sample characteristics of the 40ar 39ar age spectra depend upon grain size with fine sizes yielding discordant patterns which systematically increase in apparent age from low to high temperature and 4 phengitic micas associated with earliest structures yield generally older ages than micas associated with later structures the isotopic results are interpreted to indicate that the major deformation phase d1 occurred at approximately 27 ma with subsequent pulses ending by c 10 ma these results may be combined with finite strain data to suggest that the region was deformed at strain rates between 10 15 and 10 14 s 1 a 27 ma age indicates mid oligocene initiation of plate tectonic activity in the western mediterranean and concomitant deformation in the northern apennines

seismic multiplets analysis and its implication in seismotectonics abstract doublets analysis techniques suitable to obtain very accurate determination of arrival times of seismic phases on different stations are presented these methodologies represent a very powerful tool to recognize the seismotectonic structures and to study the propagation characteristics of seismic waves the signals similarity analysis performed in the frequency and time domain has been applied to increase the precision in arrival times definition of seismic phases generated by the same sources and having the same path tests on synthetic events have shown how it is possible to recognize the time delay between digital traces with a sensitivity less than the sample rate in particular in the time domain analysis the results obtained using different interpolation functions parabolic and sinc for the cross correlation operator are compared the analysis slightly suffers from a random noise component added to the signal allowing the phase picking of highly noised traces on the contrary the frequency domain analysis offers the best results in case of high signal to noise ratio while it appears less robust with respect to high noise influence the application of relative location techniques on the obtained arrival times allows to define with very high detail the geometrical shape of seismogenetic structures as an example a case of spatial doublets recorded by the seismic network of northwestern italy that occurred during two days in an area of the maritime alps italy has been considered in spite of the low magnitude of the events an accurate reconstruction of the spatial distribution of the sources was obtained allowing to discriminate the fault plane from the auxiliary one in the focal mechanism solution

three dimensional segmentation and different rupture behavior during the 2012 emilia seismic sequence northern italy describing the slip behavior of an active fault system is central to understanding the seismic potential of seismogenic areas different elements control the nature and the extent of the coseismic and post seismic ruptures including the geometry of faults the nature of faulted rocks and the stress changes caused by the mainshocks in may june 2012 a severe seismic sequence struck a portion of the po plain northern italy where a thick blanket of plio quaternary sediments hides a number of seismogenic sources corresponding to the external thrust systems of the northern apennines we used deep seismic reflection data to reconstruct the geometry of the faults responsible for the sequence these faults exhibit significant non planarity due to tectono stratigraphic heterogeneities inherited from a complex pre thrusting extensional tectonic phase a comparison of the fault parameters derived from our geological analysis and the evidence supplied by seismological aftershock distributions and geodetic data insar allowed to identify the causative fault segments of the two mainshocks we then modeled the coulomb stress changes produced by two mainshocks to analyze on and off fault seismicity discrepancies between the magnitude of the earthquakes and the extent of active faults suggest that the mainshocks did not rupture the entire thrust planes we contend that seismogenic ruptures were confined in the mesozoic carbonates and were stopped by lithological changes and or mechanical complexities of the fault planes both along dip and along strike our findings highlight that along the active structures of the po plain slip tends to be seismogenic where faults are located in mesozoic carbonate rocks

the tyrrhenian apennines system structural setting and seismotectogenesis abstract the available geological geophysical and seismological data of the tyrrhenian apennines system are briefly reviewed and synthesized in a number of sketch maps integrating and comparing these data a large scale simple shear kinematic model is proposed for the tyrrhenian apennines system that is here interpreted as an oblique asymmetric passive continental margin developed during the progressive counterclockwise rotation of the adriatic foreland from the late miocene to the present in the frame of this working hypothesis the thinning and stretching of the tyrrhenian crust were accommodated by progressive eastward motion of extensional allochthonous slices bounded by low angle west dipping oblique shear zones rotating above a common detachment that penetrates into the mantle lithosphere at any given time the most external eastward moving slice is bounded by a transtensional shear zone at the top and by a transpressional one at the bottom the displacement within the hanging wall of the transtensional shear zone is accommodated by high angle normal faults and en echelon grabens the displacement within the hanging wall of the transpressional shear zone is instead accommodated by co axial en echelon sets of folds thrusts and high angle strike slip faults thus the development of the late miocene pliocene pleistocene contractional strain field of the apennines of italy might not be a consequence of complex subduction processes but subordinate to the deformation processes that lead to the progressive opening of the tyrrhenian sea the seismicity of the crustal apennines of italy is analyzed in the frame of the above history of progressive deformation and a seismotectogenetic model is outlined

response of total and eddy kinetic energy to the recent spinup of the beaufort gyre abstractthe beaufort gyre in the arctic ocean has spun up over the past two decades in response to changes of the wind forcing and sea ice conditions accumulating a significant amount of freshwate

the arctic circumpolar boundary current we present high resolution simulations and observational data as evidence of a fast current flowing along the shelf break of the siberian and alaskan shelves in the arctic ocean thus far the arctic circumpolar boundary current acbc has been seen as comprising two branches the fram strait and barents sea branches fsb and bsb respectively here we describe a new third branch the arctic shelf break branch asbb we show that the forcing mechanism for the asbb is a combination of buoyancy loss and non local wind creating high pressure upstream in the barents sea the potential vorticity influx through the st anna trough dictates the cyclonic direction of flow of the asbb which is the most energetic large scale circulation structure in the arctic ocean it plays a substantial role in transporting arctic halocline waters and exhibits a robust seasonal cycle with a summer minimum and winter maximum the simulations show the continuity of the fsb all the way around the arctic shelves and the uninterrupted asbb between the st anna trough and the western fram strait the bsb flows continuously along the siberian shelf as far as the chukchi plateau where it partly diverges from the continental slope into the ocean interior the alaskan shelf break current asc is the analog of the asbb in the canadian arctic the asc is forced by the local winds and high upstream pressure in bering strait caused by the drop in sea surface height between the pacific and arctic oceans

post collisional tectonics in the northern cottian alps italian western alps field mapping and structural analysis have allowed us to characterise the fault geometry and the post metamorphic tectonics of an area located in the northern cottian alps inner western alps two main faulting stages were distinguished here the first oligocene early miocene is related to the development of an e w striking left normal shear zone this shear zone is interpreted as an antithetical of two regional n s right lateral structures the col del lis trana deformation zone ltz and the colle delle finestre deformation zone cfz the second faulting stage post early miocene is related mainly to the development of n s normal faults coeval with the extensional reactivation of the ltz and the cfz we discuss this kinematic evolution in the framework of the geodynamic evolution of the western alps

the origin of the apenninic arcs abstract the apennine area is composed of a variety of arcs some of them forming the mountain chain and some of them being submerged below the po plain and the adriatic sea the structure of the apennine mountain belt is that of a succession of northeast east and southeastward directed arcs corresponding to single thrust sheets each arc is limited by n s oriented dextral transcurrent faults data from volcanology gravimetry and reflection seismic surveys show that an important section of the upper mantle is involved in these features the geodynamic reconstruction during neogene times i e the period of apenninic up building suggests that a unique arc existed from oligocene to middle miocene times as a result of the rotation of the sardo corso continental block this arc was successively disrupted in several segments which advanced and shortened differentially as a function of the resistance to the orogenic expansion opposed by the rigid adriatic foreland this new tectonic phase which is responsible for most of the apenninic features has been triggered by the differential evolution of anomalous mantle domes in the tyrrhenian area from post middle miocene times onwards

wind driven freshwater buildup and release in the beaufort gyre constrained by mesoscale eddies recently the beaufort gyre has accumulated over 20 km3 of freshwater in response to strong anticyclonic atmospheric winds that have prevailed over the gyre for almost two decades here we explore key physical processes affecting the accumulation and release of freshwater within an idealized eddy resolving model of the beaufort gyre we demonstrate that a realistic halocline can be achieved when its deepening tendency due to ekman pumping is counteracted by the cumulative action of mesoscale eddies based on this balance we derive analytical scalings for the depth of the halocline and its spin up time scale and emphasize their explicit dependence on eddy dynamics our study further suggests that the beaufort gyre is currently in a state of high sensitivity to atmospheric winds however an intensification of surface stress would inevitably lead to a saturation of the freshwater content a constraint inherently set by the intricacies of the mesoscale eddy dynamics

exhumation of alpine high pressure rocks insights from petrology of eclogite clasts in the tertiary piedmontese basin ligurian alps italy the study of late and postorogenic sedimentary basins is a powerful tool to understand uplift exhumation and erosion of an orogen in the ligurian alps high pressure ophiolitic rocks are directly overlain by the sediments of the tertiary piedmontese basin tpb the conglomerates at the bottom of the tpb succession contain clasts of metaophiolites and metasediments which display deformation structures acquired at peak metamorphic conditions ranging from eclogite to blueschist facies the deformation events prevalently recorded by the high pressure rocks of the ligurian alps are either related to subduction and peak metamorphism or to the late stage greenschist collision the main structures which accomplish the early exhumation of such high pressure terrains are only locally recorded and poorly explored further information on these early tectonic events can be gathered through the study of the clasts in the conglomerates in this paper we present a textural and petrologic outline and some thermobarometric estimates of the main types of high pressure clasts sampled and their comparison with the high pressure equivalents presently exposed in the ligurian alps in particular some clasts displaying a na amphibole white mica epidote sphene blueschist foliation superimposed to an eclogitic garnet na clinopyroxene rutile tectonitic assemblage have been studied in detail this kind of rock records a pressure temperature p t path implying cooling during exhumation whereas the high pressure bedrocks are characterized by either isothermal decompression or initial heating and subsequent cooling we conclude that the blueschist foliation of these clasts most likely developed along shear zones and or contacts among different slices formed during tectonic coupling of warm uprising eclogite units with cooler blueschist slices during the early stages of exhumation

sources of eddy kinetic energy in the labrador sea experiments with a suite of north atlantic general circulation models are used to examine the sources of eddy kinetic energy eke in the labrador sea a high resolution model version 112 quantitatively reproduces the observed signature a particular feature of the eke in the labrador sea is its pronounced seasonal cycle with a maximum intensity in early winter as already found in earlier studies based on altimeter data in contrast to a previously advanced hypothesis the seasonally varying eddy field is not related to a forcing by high frequency wind variations but can be explained by a seasonally modulated instability of the west greenland current wgc the main source of eke in the labrador sea is an energy transfer due to reynolds interaction work barotropic instability in a confined region near cape desolation where the wgc adjusts to a change in the topographic slope geostrophic contours tend to converge upstream of cape desolation such that the topographically guided wgc narrows as well and becomes barotropically unstable the eddies spawned from the wgc instability area dominating the eke in the interior labrador sea are predominantly anticyclonic with warm and saline cores in the upper kilometer of the water column while the few cyclones originating as well from the instability area show a more depth independent structure companion experiments with a model exhibit the strength of the wgc influenced by either changes in the wind stress or heat flux forcing as a leading factor determining seasonal to interannual changes of eke in the labrador sea

on the circulation of atlantic water in the arctic ocean an idealized eddy resolving numerical model and an analytic three layer model are used to develop ideas aboutwhatcontrolsthecirculationofatlanticwaterinthearctic ocean thenumericalmodelisforcedwith a surface heat flux uniform winds and a source of low salinity water near the surface around the perimeter of an arctic basin despite this idealized configuration the model is able to reproduce many general aspects of the arctic ocean circulation and hydrography including exchange through fram strait circulation of atlantic water a halocline ice cover and transport surface heat flux and a beaufort gyre the analytic model depends on a nondimensional number and provides theoretical estimates of the halocline depth stratification freshwater content and baroclinic shear in the boundary current an empirical relationship between freshwater content and sea surface height allows for a prediction of the transport of atlantic water in the cyclonic boundary current parameters typical of the arctic ocean produce a cyclonic boundary current of atlantic water of o 1 2 2sv where 1sv 10 6 m 3 s 21 and a halocline depth of o 200m in reasonable agreement with observations the theory compares well with a series of numerical model calculations in which mixing and environmental parameters are varied thus lending credibility to the dynamics of the analytic model in these models lateral eddy fluxes from the boundary and vertical diffusion in the interior are important drivers of the halocline and the circulation of atlantic water in the arctic ocean

oligo miocene rotation of sardinia kar ages and paleomagnetic data of tertiary volcanics abstract conventional k ar dating was carried out on mineral separates mostly plagioclases from middle tertiary volcanics of sardinia along with paleomagnetic studies the close agreement of dates from the two methods establishes the rotation age of sardinia relative to europe within a rather short time span of 1 5 ma between 20 5 and 19 ma from correlation of our results with the geomagnetic time scale it is suggested that the rotation took place shortly after the magnetic anomaly 6

the valencia trough and the origin of the western mediterranean basins abstract evolutionary models for the valencia trough must be necessarily related to the neogene present geodynamics of the western mediterranean basins all these basins occupy new space created in the wake of the westward translation of the alboran block and the counter clockwise rotation of the corso sardinian block this escape tectonics microplate dispersal model can account for the co existence and progressive migration of compressional and extensional strain fields within the africa europe broad zone of convergence in this escape tectonics model the valencia trough has resulted in a complex evolution which includes 1 latest oligocene early miocene rifting along the catalan valencian margin due to the opening of the gulf of lions 2 almost simultaneous early miocene transpressive thrusting in the balearic margin related to the initiation of displacement of the alboran block and 3 late miocene generalized extension as a consequence of the opening of the south balearic basin

litho asthenospheric structures of northern italy as inferred from teleseismic p wave tomography abstract regional three dimensional inversions of teleseismic p wave travel time residuals recorded by high frequency regional and local seismic networks operating along the western alps and surrounding regions were carried out and lithosphere and upper mantle p wave velocity models down to 300 km were obtained residuals of more than 500 teleseismic events recorded by 98 fixed and temporary seismic stations have been inverted the comparison between real residuals and the ones obtained from tomographic model indicates that the method is able to solve the feature of the regional heterogeneities where the resolution is good coherent lithospheric and upper mantle structures are imaged in the shallower layers high and low velocity anomalies follow the structural behaviour of the alpine apenninic chains showing the existence of very strong velocity contrasts in the deepest layers velocity contrast decreases however two deep seated high velocity structures are observed the most extended in depth and approximately trending ne sw has been interpreted as a wreck of the oldest subduction responsible of the alpine orogenesis the second one connected to the northwestern sector of the apenninic chain appears to vanish at depths greater than 180 km and is probably due to still active apenninic roots cross sections depict the spatial trend of perturbations and in particular outline the sub vertical character of the alpine and apenninic anomalies under the ligurian sea the 3 d inversion confirms the uplift of the asthenosphere in agreement with the tectonic evolution of the basin

the early stages of the alpine collision an image derived from the upper eocene lower oligocene record in the alps apennines junction area the upper eocene lower oligocene sediments deposited in the eastern part of the tertiary piedmont basin in northern italy provide a complete record of the unroofing of the alpine orogenic prism during the early stages of exhumation in the ligurian sector from late priabonian till late rupelian time the sediments in the study area were derived from two different sources one characterised by white micas with sib6 5 pfu and permian 40 ar 39 ar ages 270 ma and the other characterised by white micas with sin7 pfu and eocene oligocene 40 ar 39 ar ages 32 50 ma the first source is considered to be indicative of low pressure metamorphic rocks that covered the hp rocks of the ligurian alps and were completely eroded by chattian time from this time on the study area started to record the first input from western alpine sources characterised by a larger span of ages with a more frequent eoalpine signal thus sediments deposited in the eastern part of the tertiary piedmont basin contain the only available evidence of rocks belonging to high crustal levels in the alpine orogenic prism that were not affected by the alpine overprint these data also provide time constraints to the poorly dated first conglomerates deposited in this area 40 ar 39 ar geochronology reveals a minimum age of 33f1 4 ma for the pianfolco conglomerates in the type locality and of 31 4f3 5 ma for the borbera conglomerates d 2004 elsevier b v all rights reserved

evolution of the eddy field in the arctic ocean s canada basin 2005 2015 the eddy field across the arctic ocean s canada basin is analyzed using ice tethered profiler itp and moored measurements of temperature salinity and velocity spanning 2005 to 2015 itps encountered 243 eddies 98 of which were anticyclones with approximately 70 of these having anomalously cold cores the spatially and temporally varying eddy field is analyzed accounting for sampling biases in the unevenly distributed itp data and caveats in detection methods the highest concentration of eddies was found in the western and southern portions of the basin close to topographic margins and boundaries of the beaufort gyre the number of lower halocline eddies approximately doubled from 2005 2012 to 2013 2014 the increased eddy density suggests more active baroclinic instability of the beaufort gyre that releases available potential energy to balance the wind energy input this may stabilize the gyre spin up and associated freshwater increase

calcite mylonites in the central alpine root zone abstract north of the insubric line in the central alpine root zone carbonate rocks are concentrated in very narrow zones and have been metamorphosed under amphibolite facies conditions by the tertiary lepontine metamorphism grain size 1 mm post metamorphic deformation under greenschist facies conditions produced calcite mylonite bands a few millimeters to tens of meters wide in these marble zones microstructural development begins with twin formation bending of twin boundaries grain and twin boundary migration and recrystallization in high stress regions progressive mylonitization by dynamic recrystallization results in a microstructure with elongated calcite crystals long axis 20 50 m axial ration 1 4 in this fine grained matrix porphyroclasts of calcite quartz white mica biotite diopside tremolite scapolite and plagioclase are preserved ultra mylonite bands in pure calcite rocks show an even finer grain size of 5 10 m lattice preferred orientation is not present in the undeformed marbles but it develops during mylonitization the c axis orientation in the mylonites forms an asymmetric point maximum in the ultra mylonite no preferred orientation is left it is concluded from microstructural and textural aspects that during mylonitization dislocation creep accompanied by dynamic recrystallization were the most important processes whilst grain boundary sliding was the dominant mechanism during the formation of the ultra mylonites shear sense determinations indicate a horizontal right lateral strike slip shear system this is in good agreement with evidence regarding other movements along the insubric line which can be observed in ductile and brittle shear zones

subsidence stress regime and rotation s of a tectonically active sedimentary basin within the western alpine orogen the tertiary piedmont basin alpine domain nw italy the oligocene to miocene tertiary piedmont basin tpb is located in the nw part of italy at the junction between the apennine and the alpine thrust belts the position of the tpb on top of the alpine apennine orogen poses fundamental questions as to the tectonics of the basin subsidence having undergone little deformation the tpb sediments provide an insight into the stress regime and rotations in the kinematically very complex area surrounding the basin itself in this study we integrate subsidence and structural analysis with measurements of magnetic susceptibility anisotropy ams and natural remanent magnetization nrm in order to better constrain the tectonic kinematics of the basin evolution a major important period of subsidence occurred in the middle miocene involving the whole basin during this period the tpb experienced ne sw directed compression and limited shortening some nw se directed compressional features have been identified and they were probably active during post tortonian times structures associated with north south tension are quite common but the amount of strain that they accommodate is minor in addition this research provides new preliminary data suggesting counterclockwise rotation in the tpb by c 20o which has taken place during middle miocene time

a kinematic evolutionary model for the penninic sector of the central ligurian alps the nappe pile presently cropping out in the central sector of the ligurian alps is represented by some principal groups of tectonic units starting from the foreland the outer and lower weakly metamorphic up to 0 3 gpa brianconnais units support the high pressure up to 1 3 gpa ensemble of inner brianconnais nappes in turn overridden by the prepiedmont units sourced from the european continental margin prepiedmont units form two superposed groups the lower is composed only of a pre namurian basement alpine metamorphism up to 0 6 gpa and the upper is mainly composed of a slightly metamorphic greenschist facies post namurian cover at the top lie the high pressure metamorphosed up to 0 8 gpa in the sector here considered ophiolitic units the group of the non metamorphic helminthoid flysch nappes original stratigraphic cover of the ophiolitic units has travelled the greatest distance and is presently mainly set onto the outer part of the chain only events up to the stacking of the nappe pile are discussed disregarding late stage deformation as the examined sector is located at a considerable distance from the collisional zone late processes did not change the overall order of superposition formerly acquired the model proposes the development of two major subhorizontal detachment surfaces the first shallower one confines at the base a very thin skinned set of nappes nearly totally made up of prepiedmont sedimentary covers that are bounded at their top by the helminthoid flysch units both these groups underwent a mainly horizontal outwards transport in contrast the underlying prepiedmont crust and the adjoining brianconnais inner sector separated by the second deeper major detachment surface were progressively dragged into the subduction zone under the ophiolitic units and duplexes were generated exhumation of the metamorphic units occurred along the subduction channel as did stacking of the nappe pile

the suture between the alps and apennines in the ligurian sector based on geological and geomagnetic data abstract a ground magnetic survey was carried out over a wide area of northwestern italy including western and central liguria the southeastern piedmont and a part of the ligurian sea several cross sections cutting the main structural elements the ligurian sea the ligurian alps the monferrato hills have been performed and magnetic models have been developed the interpretation of the most characteristic cross section a1 nnw is presented in this paper a model involving the presence of a major suture between the ligurian alps and the monferrato hills fits the positive magnetic anomaly running from the surroundings of turin towards asti this model implies that slabs of upper mantle or lower continental crust were trapped in the suture as in the internal zone of the western alps where the ivrea body comes in contact at depth with the pennidic nappes to the south this suture line does not appear throughout the ligurian sea probably owing to the recent crustal thinning which is revealed by both the magnetic and the gravimetric features

european cenozoic rift system abstract the european cenozoic rift system extends from the coast of the north sea to the mediterranean over a distance of some 1100 km it finds its southern prolongation in the valencia trough and a plio pleistocene volcanic chain crossing the atlas ranges development of this mega rift was paralleled by orogenic activity in the alps and pyrenees major rift domes accompanied by subsidence reversal of their axial grabens developed 20 40 ma after beginning of rifting uplift of the rhenish shield is related to progressive thermal lithospheric thinning the vosges black forest and the massif central domes are probably underlain by asthenoliths emplaced at the crust mantle boundary evolution of this rift system is thought to be governed by the interaction of the eurasian and african plates and by early phases of a plate boundary reorganization that may lead to the break up of the present continent assembly

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

testing models of orogen exhumation using zircon u th he thermochronology insight from the ligurian alps northern italy testing models of orogen exhumation requires precise constraint of the time temperature paths of the exhumed rocks the zircon u th he zhe thermochronometer has a closure temperature of 140 210 c and can provide temporal constraints on the exhumation history of rocks through a thermal range which crucially corresponds the onset of brittle behaviour of an exhuming orogen we performed zhe analyses to test the existing contradictory models for the exhumation of the ligurian alps the zhe ages indicate a very rapid 1 3 6 8 mm yr and southward migrating exhumation of the orogen between 32 and 25 ma these high exhumation rates are unique within the alpine belt and cannot be reconciled with existing geodynamic models of the evolution of the ligurian alps we propose a model of tectonic denudation via detachment accomplished in the shallowest crust 5 km as a result of the last orogenic phase of extension

salt tectonics in the sw alps italy france from rifting to the inversion of the european continental margin in a context of oblique convergence abstract the sw alps result from the inversion of the european continental margin during the oblique convergence between europe and adria since the cretaceous the orogenic deformation is controlled by two factors the inherited sedimentary and structural record and the geodynamic interaction between the two plates in this paper we present a stratigraphic and structural analysis of the external sw alps ventimiglia menton area in order to define the sedimentary and deformational geometries of the chain and to reconstruct the evolutionary history the field data highlight the preeminent role played by inherited salt structures which derive from the depositional history experienced by the european margin since the mesozoic onwards from late triassic to jurassic evaporites and carbonates deposited as a response to the thetyan rifting the following emplacement of the cretaceous flysch and of the eocene foreland basin succession was strongly influenced by the extensionally triggered salt diapirism and by the interactions with deformations connected to the pyrenees dynamics the resulting geologic discontinuities i e diapir induced highs and basins inherited normal and trasform faults strongly influenced the successive oligo miocene evolution of the belt in the study area observed changes in the thrusts and folds kinematics are considered as the results of rotation during their approaching to inherited highs furthermore the overturning of thrusts and folds in the front of the diapiric flanks are associated with the progressively salt squeezing into the anticlines cores promoted by ongoing alpine compression finally the kinematic data from the study area show radical differences in the tectonic transport direction with respect to the rest of the sw alps nw to w ward in the ventimiglia menton area s to sw ward in provence and ligurian alps this difference is interpreted to be caused by the relative motions of crustal blocks dominated by transpressive tectonics in the frame of the oligo miocene western mediterranean geodynamics

observations of seasonal upwelling and downwelling in the beaufort sea mediated by sea ice abstractwe present observational estimates of ekman pumping in the beaufort gyre region averaged over the canada basin the results show a 2003 14 average of 2 3 m yr 1 downward with strong seasonal and interannual variability superimposed monthly and yearly means range from 30 m yr 1 downward to 10 m yr 1 upward a clear seasonal cycle is evident with intense downwelling in autumn and upwelling during the winter months despite the wind forcing being downwelling favorable year round wintertime upwelling is associated with friction between the large scale beaufort gyre ocean circulation and the surface ice pack and contrasts with previous estimates of yearlong downwelling as a consequence the yearly cumulative ekman pumping over the gyre is significantly reduced the spatial distribution of ekman pumping is also modified with the beaufort gyre region showing alternating moderate upwelling and downwelling while a more intense yearlong downwelling averaging 18 m yr 1 is identified in the northern

relationships among properties of marine stratocumulus derived from collocated calipso and modis observations 1 collocated moderate resolution imaging spectroradiometer modis imagery and cloud aerosol lidar and infrared pathfinder satellite observation calipso 532 nm total attenuated backscatter coefficients were used to identify 50 km scale segments for ocean regions that had only a single layer of marine stratocumulus on the basis of whether the underlying ocean surface was detected in the backscatter coefficients the segments were separated into those for which all of the 1 km modis pixels were identified as being overcast no surface detected and those for which there were breaks in the cloud layer surface detected cloud properties for the collocated modis pixels were obtained from the modis mod06 cloud product and from a retrieval scheme designed to account for broken clouds within imager pixels for the 50 km overcast segments the variations in optical depth and droplet effective radius re obtained from the mod06 and partly cloudy pixel retrievals were in agreement and the variations in layer temperature were consistent with those inferred from the calipso backscatter coefficients in addition the droplet effective radii retrieved separately using the 1 6 2 1 and 3 7 m modis reflectances were consistent with droplets growing as clouds thickened and mean values of dlnre dln were close to 0 2 as predicted by adiabatic cloud parcel models when the segments contained broken clouds however the droplet effective radii for the three near infrared wavelengths were inconsistent with droplets growing as clouds thickened and dlnre dln departed from 0 2 this breakdown is thought to result from biases in the retrieved cloud properties caused by subpixel scale variations in liquid water amount and droplet radius

dynamics of isolated convective regions in the ocean abstract an initially resting ocean of stratification n is considered subject to buoyancy loss at its surface of magnitude b0 over a circular region of radius r at a latitude where the coriolis parameter is f initially the buoyancy loss gives rise to upright convection as an ensemble of plumes penetrates the stratified ocean creating a vertically mixed layer however as deepening proceeds horizontal density gradients at the edge of the forcing region support a geostrophic rim current which develops growing meanders through baroclinic instability eventually finite amplitude baroclinic eddies sweep stratified water into the convective region at the surface and transport convected water outward and away below setting up a steady state in which lateral buoyancy flux offsets buoyancy loss at the surface in this final state quasi horizontal baroclinic eddy transfer dominates upright plume convection by using parcel theory to consider the energy transformations taking place it is shown that the de

the shape propagation and mean flow interaction of large scale weather systems abstract for a zonal average operator the eliassen palm flux provides a diagnostic of both eddy behavior and the feedback of the eddies onto the mean flow this paper addresses the diagnosis problem for other averaging operators and in particular for time averaging which has proved in recent years such a powerful means of viewing the three dimensional tropospheric flow the horizontal velocity correlation tensor gives a measure of the characteristic horizontal eddy shape at a point it also implies the direction of the group velocity relative to the mean flow in cases where such a concept is valid however the major emphasis here is on the mean flow feedback of eddies in this respect the eddy vorticity flux is determined by derivatives of the components of the anisotropic part of the tensor making a reasonable approximation allows the eddy vorticity flux convergence to be written in terms of e v 2 u 2 u v a simple interpretation of the mean flow feedback of eddies is then possible a sligh

opposite verging chains sharing the same foreland kinematics and interactions through analogue models central po plain italy abstract in this study we investigate the potential role played by different geological factors on the development of a thrust system in particular our goal is to analyze how pre existing compressional structures located in the foreland of a thrust and fold belt may affect the kinematics of a thrust system we studied such circumstances both in a natural case and through analogue models as a natural case we selected the central po plain italy where the buried external fronts of the northern apennines and southern alps are very close to each other starting from a regional cross section representative of this tectonic setting we reconstructed the post messinian development of the apennines thrust fronts which includes out of sequence thrusting then we modeled this evolution through a set of analogue experiments to evaluate the possible relationships of the out of sequence thrusting with the burial of the syntectonic sediments and or the existence of the outer fronts of an opposite verging chain in its foreland the comparison between natural case and models highlights that the presence of opposite verging thrust fronts in the foreland of a belt limits the propagation of new thrusts favoring the out of sequence reactivation of inner thrusts an analysis of the study area with respect to adjacent tectonic settings coupled with analogue models revealed that syntectonic sedimentation as well has a role in the reactivation of the inner fronts although secondary in the po plain specific case this implies that the presence of the buried southern alps fronts affects the northern apennines kinematics even if the two fronts did not collide yet

influence of structural inheritance on foreland foredeep system evolution an example from the po valley region northern italy understanding the development of foreland foredeep systems and the influence exerted by pre existing structures on their evolution is an important step for defining the key factors that control long term basin and lithosphere dynamics comprehending the associated seismic hazard and assessing their economic potential in the domain of hydrocarbon exploration the po valley is a rather unique foreland basin for two major reasons a it developed intermittently at the front of two different mountain chains the northern apennines and the southern alps progressively converging one towards the other b the inherited structures mainly derived from the mesozoic extensional tectonics are oriented at high angle to the advancing belts the coexistence of these two factors and their various implications make the po valley basin a complex case study that deserves attention taking advantage of the recent building of a 3d structural model across the region we reconstructed the possible geometry and migration pattern of the tertiary basins that developed at the front of the northern apennines and the southern alps as part of the po valley tectonic evolution in addition a number of sections sliced from the 3d model across selected domains have then been used to restore the present day structural units to their pre compressional setting while highlighting the key stages of their geological history results from the model analysis show that the mesozoic extension related tectonics and the associated carbonate facies geometry and distribution localized and constrained the alpine structures inside around the basin their control on the cenozoic deformation and sedimentation is evident during the paleogene and the miocene whereas it becomes more subtle during the plio pleistocene when lithospheric scale mechanisms need to be invoked notwithstanding the model uncertainties and its explicit regional significance our results may be taken as reference for any foreland foredeep setting worldwide especially in complex systems where tectono sedimentary inhomogeneity is spatially and temporally dominant

the role of pre existing faults in the structural evolution of thrust systems insights from the ligurian alps italy abstract new structural and stratigraphic data for a selected area of the ligurian alps are combined in order to assess and discuss the role played by extensional structures in the southernmost segment of the western alps during thrusting restored cross sections and field data suggest that the structural style in the external sector of the chain may depend upon the presence of pre orogenic normal faults ascribed to three extensional events linked to different geodynamic contexts i permian post variscan plate reorganisation ii mesozoic rifting drifting phases leading to the opening of the alpine tethys and iii eocenic development of the european foreland basins during positive inversion in eocene times a thin skinned thrust system developed in this area followed by a thick skinned phase in both situations the inherited extensional structures played fundamental roles during the thin skinned phase they conditioned the thrusting sequence also producing large scale buckle folds and partial reactivations during the thick skinned phase the strain was compartmentalized and partitioned by pre existing faults the kinematic model of the external sectors of the ligurian chain also allows the re assessment of the alpine evolution of the front foreland transition including i indirect confirmation that in the eocene the ligurian brianconnais and dauphinois domains were not separated by the valais pyrenean oceanic basin ii that the thin skinned phase progressively changed into thick skinned iii the assertion that there were no significant deformations from the oligocene to the present day and the corsica sardinia block rotation only produced a change in orientation of previously formed structures and normal fault system development

kinematics of the alpine arc and the motion history of adria the alps have been interpreted traditionally in terms of north or northwest directed convergence between africa and europe1 with adria the continental underpinnings of the adriatic sea and northern italy acting as a promontory of the african continent2 this has been supported by recent analyses of africa europe relative plate motions3 5 which indicate dominantly north south directed convergence during the tertiary phase of intracontinental shortening we show here however that kinematic indicators from alpine tectonites are difficult to reconcile with this motion history figs 1 and 2 and are explained best by roughly west northwest directed adria europe motion since about 70 million years ago combined with an arc normal pattern of motion driven by local body forces this implies that adria has moved independently of both africa and europe since at least the late cretaceous

decollement depth versus accretionary prism dimension in the apennines and the barbados 1 along representative cross sections of the apennines and the northern barbados accretionary prisms we measured the area the decollement depth the angle a of the upper envelope and the angle b of the dip of the regional monocline the continental sections of the apennines accretionary prism have a deeper decollement than the oceanic sections of the northern barbados 6 10 km depth and 1 km depth respectively because the sediment pile is thinner on the incoming barbados plate and its denser oceanic structure is more easily subducted considering the frontal 50 km the apennines have an average cross sectional area of 500 km 2 and the northern barbados ridge of 100 km 2 the total area is a function of the depth of the decollement plane therefore at a given amount of subduction the deeper the decollement depth is the bigger the area of the wedge will result assuming negligible compaction and erosion as a consequence the larger area volume and higher elevation of the apennines with respect to the barbados is determined by the apenninic deeper decollement despite these differences the geometry of both decollements is in some cases comparable in particular close to the boundary between the crystalline crust and the sediment pile where the main density and strength contrasts are concentrated variations in depth of the decollement occur moving along strike in both accretionary prisms the geometry of the prisms is further controlled by the different values of a and b their sum and the distance of the accretionary prism relative to the subduction hinge index terms 8099 structural geology general or miscellaneous 8150 tectonophysics evolution of the earth plate boundary general 3040 8122 tectonophysics dynamics gravity and tectonics keywords decollement depth accretionary prism apennines barbados citation bigi s f lenci c doglioni j c moore e carminati and d scrocca decollement depth versus

beaufort gyre freshwater reservoir state and variability from observations 1 we investigate basin scale mechanisms regulating anomalies in freshwater content fwc in the beaufort gyre bg of the arctic ocean using historical observations and data collected in 2003 2007 specifically the mean annual cycle and interannual and decadal fwc variability are explored the major cause of the large fwc in the bg is the process of ekman pumping ep due to the arctic high anticyclonic circulation centered in the bg the mean seasonal cycle of liquid fwc is a result of interplay between the mechanical ep and thermal ice transformations factors and has two peaks one peak occurs around june july when the sea ice thickness reaches its minimum maximum ice melt the second maximum is observed in november january when wind curl is strongest maximum ep and the salt input from the growing ice has not yet reached its maximum interannual changes in fwc during 2003 2007 are characterized by a strong positive trend in the region varying by location with a maximum of approximately 170 cm a 1 in the center of ep influenced region decadal fwc variability in the period 1950 2000 is dominated by a significant change in the 1990s forced by an atmospheric circulation regime change the center of maximum fwc shifted to the southeast and appeared to contract in area relative to the pre 1990s climatology in spite of the areal reduction the spatially integrated fwc increased by over 1000 km 3 relative to climatology