paleoceanographic and climatic implications of a new mediterranean outflow branch in the southern gulf of cadiz abstract the presence of contourite drifts in the southern gulf of cadiz goc along the moroccan margin raises questions about the re circulation of mediterranean outflow water mow in the goc and the origin of the currents depositing them here we compare two cores representative of iberian and moroccan contourite drifts covering the last 22 kyr although the whole sequence is contouritic in character it reflects the interaction of distinctive silty contourite facies high flow velocity periods imbedded in muddy contourite facies low flow velocity periods evidence from benthic foraminifera 13c sortable silt grain size oceanographic ctd profiles and numerical simulations indicate the mediterranean water mass as the source of the southern contourite deposits our data therefore suggests an additional branch of upper mow veering southwards off the straits of gibraltar along the moroccan margin during mis marine isotope stage 2 upper mow was a sluggish current while in the holocene upper mow dominated as a fast semi steady flow throughout the deglaciation silty contourites associated with higher flow speeds were deposited in the northern and southern goc during cold events such as heinrich stadial 1 hs1 and the younger dryas forced by global millennial scale climate variability millennial variability also appears to drive the deposition of silty contourites in the holocene we estimated an average duration of 1 ka for the process of depositing a fast contourite unit the case of silty contourite i6 within hs1 allows us to illustrate with extremely high resolution a rapid sequential change in circulation with gradual slow down of dense mediterranean water while surface was freshening hs1 provoking injection of high salinity intermediate waters via contour currents into the goc and hence the north atlantic the subsequent brief collapse of dense water formation in the mediterranean sea triggered a major increase in sea surface temperatures 10 c ka in the goc developing into the next interstadial bolling allerod the impact of mediterranean intermediate waters is manifested here by triggering a substantial rearrangement of intermediate and deep circulation in the north atlantic which would have further impacted the atlantic meridional overturning circulation amoc

laboratory measurements of electrical conductivity of hydrous and dry silicic melts under pressure an interpretation of the electrical signature of molten rocks within the earth s interior in terms of nature and temperature conditions of magma requires additional laboratory data on the electrical conductivity of silicate melts this paper describes an experimental setup and presents measurements of the electrical impedance of dry and hydrous 1 3 wt h2o metaluminous obsidians determined in an internally heated pressure vessel in the range of 50 400 mpa and 350 1325 c it is shown that the temperature and pressure dependences of electrical conductivity of both hydrous and dry obsidian can be fitted by an arrhenius law applying in the melt and the glass regions this suggests that a similar transport mechanism operates in both melt and glass the determined activation energies are 70 kj mol for the dry obsidian and 65 and 61 kj mol for the 1 and 3 wt h2o melts respectively the activation volume is 20 cm3 mol combination of tracer diffusion and electrical conductivity reveals that sodium is the dominant charge carrier in the hydrous and dry obsidians the temperature and pressure effects on conductivity are therefore interpreted in terms of activation energy and activation volume for na mobility in dry and hydrous rhyolites an increase in conductivity associated with addition of water was observed and is shown to reflect the effect of water incorporation in melts on the mobility of sodium as a prospective it is anticipated that both the mobility and content of sodium could control the electrical conductivity of most terrestrial silicate melts magma under differentiation becomes more conductive due to sodium and water enrichment associated with fractional crystallization therefore its electrical signature must reveal its nature and maturity

on the seasonal variability of the canary current and the atlantic meridional overturning circulation the atlantic meridional overturning circulation amoc is continually monitored along 26 n by the rapid mocha array measurements from this array show a 6 7 sv seasonal cycle for the amoc with a 5 9 sv contribution from the upper mid ocean recent studies argue that the dynamics of the eastern atlantic is the main driver for this seasonal cycle specifically rossby waves excited south of the canary islands using inverse modelling hydrographic mooring and altimetry data we describe the seasonal cycle of the ocean mass transport around the canary islands and at the eastern boundary under the influence of the african slope where eastern component of the rapid mocha array is situated we find a seasonal cycle of 4 1 0 5 sv for the oceanic region of the canary current and 3 7 0 4 sv at the eastern boundary this seasonal cycle along the eastern boundary is in agreement with the seasonal cycle of the amoc that requires the lowest contribution to the transport in the upper mid ocean to occur in fall however we demonstrate that the linear rossby wave model used previously to explain the seasonal cycle of the amoc is not robust since it is extremely sensitive to the choice of the zonal range of the wind stress curl and produces the same results with a rossby wave speed of zero we demonstrate that the seasonal cycle of the eastern boundary is due to the recirculation of the canary current and to the seasonal cycle of the poleward flow that characterizes the eastern boundaries of the oceans

electrical conductivity in a partially molten crust from measurements on metasedimentary enclaves abstract the complex electrical impedance of a garnet biotite sillimanite residual enclave in the neogene dacite of el hoyazo se spain has been determined up to 978 c at 200 300 mpa this well studied material represents a direct sampling of the alboran domain thinned lower crust undergoing partial melting the paragenesis is garnet biotite sillimanite plagioclase graphite cordierite coexisting with widespread 10 wt rhyolitic melt occurring as inclusions and interstitial glass and developed during regional anatexis at 850 50 c and 500 700 mpa the samples were used in cyclic measurements consisting in heating cooling ramps at progressively higher maximum temperature to observe the effect of reactions on conductivity in the first cycle up to 850 c at 2 3 kbar re melting of the interstitial glass is achieved with no additional reactions and logarithmic conductivity s m is up to 1 5 at t 950 c new melt with orthopyroxene ilmenite is produced from biotite partial breakdown and the logarithmic conductivity s m is up to 0 7 application of mixing models as hashin shtrikman bounds or archie s law shows that once interconnected melt controls the electrical conductivity of the enclave the electrical conductivity of the rock can be simulated with the electrical conductivity data obtained on the starting matrix glass of the enclave and with the new melt our experimental results obtained on a graphitic metasedimentary material evidence show that graphite does not contribute to the conductivity enhancement and that the electrical anomaly observed below the betics can be explained as effect of partial melting of a residual crust comparison with previous works on mafic granulites shows that similar conductivity values can be achieved both by melting of a residual felsic crust or by melting of mafic materials and suggests that pelitic rocks can be more common at deep levels than expected

heat flow heat production and lithospheric thermal regime in the iberian peninsula abstract the first heat flow and heat production maps of the iberian peninsula and its margins using previously acquired data are presented the surface heat flow map includes 553 determinations carried out on water and mining exploration wells oil exploration wells and on the seafloor the surface heat flow varies noticeably from the iberian mainland 65 10 mw m 2 to the atlantic and the mediterranean margins where the heat flow reaches values of about 40 50 mw m 2 and 80 100 mw m 2 respectively the heat production map consists of 664 determinations carried out on rock samples from the variscan iberian massif and the betics the higher values are obtained for granitic rocks 2 5 3 5 w m 3 whereas metasediments and basic rocks reach values of 1 2 5 w m 3 and nearly zero respectively the lithospheric structure deduced for the iberian peninsula by combining heat flow heat production and elevation data indicates that most of the iberian mainland is characterized by a lithospheric thickness of 110 5 km this value is maintained across the west atlantic margin whereas towards the mediterranean margin the lithospheric thickness decreases down to 60 40 km this study also suggests that the heat production in the southern variscan iberian massif must be noticeably higher 3 7 0 5 w m 3 than in the rest of the areas in order to fit the measured heat flow crustal thickness and elevation data

recent large fold nucleation in the upper crust insight from gravity magnetic magnetotelluric and seismicity data sierra de los filabres sierra de las estancias internal zones betic cordillera abstract rheological heterogeneities in the upper crust have a close relationship with the fold position where rigid bodies could constitute initial perturbations that allow the nucleation of folds consequently establish the position and geometry of anomalous rocks located in the upper crust by geophysical studies help to understand the folded structure observed on surface new geological observations in the field along with gravity magnetic magnetotelluric and seismicity data reveal the subsurface structure in the sierra de los filabres sierra de las estancias folded region part of the alpine belt in southern spain the geometry of the upper crust is determined by geological field data 2d gravity models 2d magnetic models and 2d mt resistivity model while seismicity evidences the location of the deep active structures these results allow us to propose that a basic rock body at 4 to 9 km depth has determined the nucleation and development of the sierra de los filabres kilometric antiform n vergent large late folds are subjected to a variable present day stress field earthquake focal mechanisms suggest the presence in depth of a regional nw se compressive stress field however most of the seismogenetic structures do not extend up to the surface where nw se and wnw ese outcropping active normal faults are observed thus indicating a ne sw extension in the upper crust simultaneous to orthogonal nw se compression related to reverse faults and minor folds developed in the eastern almanzora corridor and in the nearby huercal overa basin the recent and active tectonic studies of cordilleras hinterland subjected to late folding greatly benefits from the integration of surface observations together with geophysical data

constraints on the frontal crustal structure of a continental collision from an integrated geophysical research the central western betic cordillera sw spain 1 melange rocks outcrop widely in the central and western frontal sectors of the betic cordillera as in many other collisional orogens where they form part of the accretionary wedges extrusion of triassic plastic clays and evaporites was favored by the progressive accretion of the betic external zones mixing rocks of different provenance and forming a synorogenic frontal melange unit mt data coupled with gravity data are a valid combined methodology to characterize the geometry of these melange units since the characterization of plastic rocks geometry is usually uncertain using seismic techniques the results correlate well with known geological features sedimentary basins calcareous ranges evaporitic rocks and reveal the deep geometry a resistive body slightly dipping toward the se points to the continuity of the iberian massif below the guadalquivir basin 2 and the external zones 6 8 to the south gravity models show the iberian continental crust subducting below the internal zones with a roughly 20 35 slope the main conductive bodies are related to the location of evaporitic rocks involved in the frontal melange they overlie the iberian massif and southwards the frontal jurassic and cretaceous limestone sequences of the external and median subbetics in this setting thick plastic rock units placed above the foreland could act as a lubricant facilitating continental subduction and being progressively accreted toward a frontal melange

mass fluxes in the canary basin abstract ocean studies in the 1970s provided an improved knowledge of the coastal upwelling region off nw africa while in the 1980s and 1990s they led to a good description of the open ocean flow patterns in the canary basin it was not until the late 1990s that major research addressed the open coastal ocean coupled response here we examine the mean and seasonal circulation patterns in the canary basin with data from four hydrographic cruises carried out in the region between cape ghir madeira island and the canary islands we apply an inverse box model to an ocean divided into 14 layers with several layers representing each water mass or stratum to obtain mass fluxes consistent with the thermal wind equation an optimum flow description is obtained using conservation of mass salt and heat anomaly biologically corrected oxygen and silicate and allowing for ekman transport in the surface layer and dianeutral mixing between adjacent layers the deep waters show no predominant flow direction while the intermediate waters display localized southward flowing mediterranean water far from shore and northward flowing antarctic intermediate water near the continental slope specially in the passage between the eastern canary islands and the african slope the mean upper thermocline canary current composed of north atlantic central water flows south with an open ocean branch transporting about 3 1 sv 1 sv 10 6 m 3 s 1 10 9 kg s 1 and an upwelling related branch near the continental slope carrying 1 0 3 sv the seasonal transport by the open ocean branch intensifies and moves offshore from spring to fall 2 8 1 2 sv in spring 2 9 1 1 sv in summer and 4 5 1 2 sv in fall while it carries its lowest southward mass flux in winter 1 7 1 0 sv possibly as a result of a migration offshore the sampled region upwelling related southward flow is present in spring and summer 1 9 0 1 sv and 2 4 0 1 sv respectively while in fall and winter it merges with the offshore southward branch this westward migration allows a northward mass flux between the canary islands and the african coast 1 8 0 1 sv that by winter reaches cape ghir 0 5 0 2 sv seasonal air sea heat fluxes fit well with the climatological values the net phosphate transport in the surface layer indicates that primary production was negligible in this region during january 1997 and april 1998 though in this last month production was probably starting as a result of significant nutrient supply

electrical resistivity model of the crust and upper mantle from a magnetotelluric survey through the central pyrenees summary an mt profile which roughly coincides with the south side of the ecors pyrenees deep reflection seismic profile was made from the north pyrenean zone through the central pyrenees and ebro basin the periods recorded ranged from 0 0128s to 2000 s analysis of mt data shows a 2 d conductive structure the strike direction of the structure is e w parallel to the pyrenean chain interpretation of the data includes geomagnetic transfer functions and is constrained by some relevant geometric crustal features observed in seismic data accordingly a 2 d resistivity cross section has been obtained the most striking results are 1 detection of subvertical conductors in the upper crust coinciding with major fault zones 2 detection of a deep high conductivity zohe at the contact between the iberian and the european plates 3 the fact that the european plate is thicker and more resistive than the iberian one interpretation of the deep high conductivities suggests the existence of partial melting in the pyrenees related to the subduction of the iberian plate beneath europe

rapid rise of sea level 19 000 years ago and its global implications evidence from the irish sea basin supports the existence of an abrupt rise in sea level meltwater pulse at 19 000 years before the present b p climate records indicate a large reduction in the strength of north atlantic deep water formation and attendant cooling of the north atlantic at this time indicating a source of the meltwater pulse from one or more northern hemisphere ice sheets warming of the tropical atlantic and pacific oceans and the southern hemisphere also began at 19 000 years b p these responses identify mechanisms responsible for the propagation of deglacial climate signals to the southern hemisphere and tropics while maintaining a cold climate in the northern hemisphere

an electrical resistivity lithospheric model in the carpathian orogen from romania abstract magnetotelluric mt results in the carpathian orogen and its surrounding areas the scythian and moesian platforms as well as the transylvanian depression are presented joint interpretation of mt data and other geophysical information provides an approximate lithospheric model along one profile which transverses from west to east the transylvanian depression the neogene volcanic chain the flysch nappes the foreland and the moesian and scythian platforms the model reveals the alpine palaeo plane of consumption probably caused by the collision of two lithospheric plates generating the subduction exhibited in the eastern carpathians of the flysch nappes primary socles the thickness of the flysch nappes the platform basement structure and partial melting of the asthenospheric material in two depth ranges 80 100 km to the west and more than 150 km east of the palaeo plane

lateral variation of the crust in the iberian peninsula new evidence from the betic cordillera abstract new results from a seismic refraction wide angle reflection survey carried out in the betic cordillera in autumn 1989 contribute to a better picture of its deep structure one nw se profile cuts across the iberian massif the external and internal betics the structure of the crust in the iberian massif shows characteristics similar to those found in previous experiments the lower crust is found as a distinct layer 12 km thick with an average velocity of 6 8 km s 1 the moho is found at about 35 km depth this structure extends southeastward until a 3 4 km upwelling of the moho about 30 km north of the present day surface boundary between the external and internal betic units further southeast the moho deepens to 38 km and the lower crust is no longer seismically detected the absence of differentiated lower crust beneath part of the external betics may be related with the mesozoic rifting of the south iberian passive margin instead this absence under the internal betics may be caused by rifting in conjunction with the collisional evolution of the orogen a wnw ese profile lying in the internal betics shows the presence of a prominent reflector at 10 12 km depth this seems to be a widespread feature in the internal betics and may be interpreted as a detachment surface the moho is found at 38 km depth rising strongly in the easternmost betics seismic data suggest a thin crust in the offshore area southwest of malaga probably containing a massive zone of high velocity rocks which is also supported by available geophysical and geological data

canary current and north equatorial current from an inverse box model 1 the large scale canary basin circulation is estimated from a box inverse model applied to hydrographic data from a quasi synoptic survey carried out in september 2003 the cruise consisted of 76 full depth ctd and oxygen stations circulation is required to nearly conserve mass and anomalies of salinity and heat within layers bounded by neutral surfaces it permits advective and diffusive exchange between layers and an adjustment of the ekman transport and the freshwater flux divergences the canary current at the thermocline layer transports a net mass of 4 7 0 8 sv southward north of the canary islands from the african coast to 19 w it is divided into a northward circulation at a rate of 1 1 0 5 sv between the african coast and lanzarote island and a southward transport of 5 8 0 6 sv it transports north atlantic central water and organic matters advected offshore by the filaments protruding from the upwelling system off northwest africa at 24 n the canary current feeds the north equatorial current that transports a mixture of north and south atlantic central waters westward in the intermediate layer a southwestward flow of 1 2 1 1 sv transports mediterranean water to the subtropical gyre though the highest salt flux is transported by a meddy oxygen distribution and mass transport suggest a northeastward deep flow of a water mass colder than 2 2 c consisting of diluted antarctic bottom water the heat and freshwater divergences and the average dianeutral velocity and diffusion between the sections and the african coast are negligible

crustal temperature and mantle heat flow in europe abstract the map of the surface heat flow in europe was supplemented by the crustal thickness pattern and data on crustal radioactivity and transformed to the mantle moho heat flow distribution using a model of radioactivity decreasing exponentially with depth a z a 0 exp z d with a0 2 wm 3 and d 10km we computed generalized one dimensional steady state conductive temperature depth curves for the major tectonic units of europe the available information on the heat flow tectonic age heat flow heat generation and heat flow crustal thickness relationships were summarized and discussed in terms of crustal structure the mohorovicic discontinuity is clearly not an isothermal surface neither is the outflow of heat from the upper mantle constant but both parameters may vary within broad limits the moho temperature can be as low as 280 c in the shield areas however it can exceed 900 c in some young intrarnontane depressions or rift structures regional variations of the moho heat flow can be as large as 30 40 mwm 2 the value of the moho temperature reflects primarily the tectonic stabilization of the crust as a result of the deep seated processes in the upper mantle

seasonal flow reversals of intermediate waters in the canary current system east of the canary islands two 9 yr current meter and salinity records together with climatological data reveal marked seasonal variability of the intermediate flow at a key location in the canary basin the region is characterized by a summer july september and early fall october northward progression of antarctic intermediate water followed by a fall november december intense flow reversal of mediterranean water a sverdrup type model confirms that these movements are associated with stretching or shrinking of the intermediate water strata

the source of the canary current in fall 2009 1 the source of the canary current has been inferred from an inverse box model applied to the hydrographic data of a survey carried out in 2009 in the northeast subtropical gyre 29 37 n 9 24 w the portugal current is observed between 13 5 and 14 8 w at 37 n carrying 1 8 0 4 sv southward this current presumably merges with the eastward transport of the azores current system and partly contributes to the mediterranean inflow and partly to the northward recirculation of the azores current through the gulf of cadiz the azores current system is located in the meridional range 33 50 36 25 n at 24 50 w this system transports eastward 7 2 0 5 sv in the thermocline layers and 1 1 0 8 sv at intermediate layers the azores current intermediate water mass has the highest portion of sub arctic intermediate water saiw in the region while the azores countercurrent intermediate waters mass is mainly mediterranean water the canary current extends from 22 25 to 18 50 w at 29 n the westernmost position ever observed this current transports southward 6 2 0 6 sv in the thermocline layers and 2 0 0 8 sv in the intermediate layers this intermediate flow shows a relative maximum of oxygen and a relative minimum in nutrient concentration indicating the presence of saiw the study concludes that at least in fall 2009 the canary current extends to the intermediate waters n 27 9220 approximately 1600 dbar and that azores current feeds the canary current at surface and intermediate layers

laboratory measurements of seismic p wave velocities on rocks from the betic chain southern iberian peninsula abstract ultrasonic laboratory measurements of seismic compressional velocities vp carried out on rock samples encompasing a wide range of metamorphic grades and lithologies from the betic chain are presented measurements were performed at a high confining pressure on a total of 12 representative samples of the alboran domain internal betics p wave mean velocities referred to pressure conditions of 280 10 mpa range from 5 82 to 7 13 km s 1 the maximum values corresponding to high amphibolite facies metapelites garnet gneiss under these pressure conditions vp anisotropies range from 1 2 to 16 1 with the lowest values being associated with granitic rocks and the highest values associated with metapelites from the upper structural units p wave velocities were calculated for prevailing p t conditions at depths of 10 20 30 and 40 km we discuss the significance of the analyzed rock types in terms of metamorphic grade and derived vp at different crustal levels p wave velocities and densities measured on low to middle and middle to high grade metamorphic rocks are compatible with values obtained from previous seismic and gravity studies for the upper and middle crust respectively at lower crustal levels the integration of our measurements with other geophysical data suggests the presence of partial melting of high grade metamorphic rocks the estimation of the impedance contrast from the measured physical properties suggests that the reflective character of the mid lower crust is associated with shear mylonitic zones and or fine scale lithological layering enhanced by partial melting

extension versus compression during the miocene tectonic evolution of the betic chain late folding of normal fault systems the westernmost part of the mediterranean alpine belt is represented by the betic rif orogenic belt around the gibraltar arc which in turn surrounds the alboran basin in the betic chain early and middle miocene crustal thinning of the alboran basement is well established as extensional low angle normal faults and detachment faults developed in both ductile and brittle conditions thinned a previously thickened crust in the alboran domain of the central betics two main extensional episodes are evidenced a langhian one with a north northwestward transport direction followed by a west southwestward extension serravallian in age therefore all the units heretofore considered to be thrust nappes are in reality extensional units bounded by low angle normal faults the cortical segment studied formed the basement of the miocene alboran basin in which progressively deeper basement units were covered by younger marine sediments as a result of extensional denudation processes the age of these sediments clearly dates the faulting the extensional evolution during the miocene is much more complex than the past models suggest during the upper miocene these extensional systems were folded as the result of a compressive regime which allowed them to be well exposed compression in the gibraltar arc is nearly contemporaneous with extension and the westward migration of the compression through its footwall is related with the extensional spreading

signatures of the mediterranean outflow from a north atlantic climatology 2 diagnostic velocity fields part 1 of this study is a descriptive analysis of the spreading of mediterranean water based on high resolution maps of salinity and density in the eastern basin in this second part of our study velocity fields for two representative isopycnal surfaces of the mediterranean outflow o 0 s 29 70 and o 0 s 29 90 are estimated from a diagnostic model that combines climatological hydrographic data from the national oceanic data center with long term direct measurements of water exchange through the strait of gibraltar the model is constrained by geostrophic dynamics conservation of mass no flux conditions at the continental shelf and specified flow through the strait of gibraltar our principal data source is a recently assembled database of the north atlantic that consists of climatological mean property fields averaged on isopycnal surfaces the mean fields are based on more than 80 years 1909 1990 of data and have a nominal horizontal resolution of 0 5 o to provide boundary conditions at the strait of gibraltar we use the results of a model developed from data collected during the gibraltar experiment in 1985 the estimated velocity fields show mediterranean water exiting the strait of gibraltar following the southern iberian coast and then entering the tagus basin where it turns anticyclonically to create a reservoir of this water mass the flow continues northward along the eastern boundary penetrating into the rockall channel finally the model flow fields do not show a significant westward advection of mediterranean waters into the subtropical gyre

the eastern boundary current system between the canary islands and the african coast to study the easternboundarycurrentsystem off northwest africa in detail several ctd adcp sections and long term mooring work were carried out in the channel between lanzarote and africa the observations are compared with a fine resolution model which was developed in the framework of the canigo project the water masses which are observed in this area are characterised and classified in density ranges the current field shows a high spatial and temporal variability with maximum velocities of about 35 cm s seasonal means as well as currents averaged across the channel are only a few cm s in the surface water a steady southward flow in the middle of the channel indicates the canarycurrent in this area during fall a strong northward current is observed close to the african shelf though the canarycurrent strengthens during summer and fall due to an increase of the trade winds the transport in the channel decreases or turns northward during that time due to the enhanced poleward current at the eastern side a northward undercurrent with a mean velocity of 2 3 cm s is observed at the african slope in 950 m depth the poleward transport of aaiw increases during fall and a strong influence of relatively fresh aaiw is observed during that time most of the observations fit well to the results of the canigo model but the occurrence of mw at the bottom of the channel and the corresponding southward flow cannot be resolved by the model

a high electrical conductive zone at lower crustal depth beneath the betic chain spain abstract magnetotelluric data with periods of up to 2000 s were collected and the conductivity structure of the crust and upper mantle was imaged in the central betic chain interpretation of the impedance tensor components and the geomagnetic transfer functions was made in terms of a two dimensional resistivity model along a nw se profile from the guadalquivir foreland basin and across the boundary between the external and the internal betics elongated high conductivity zones in the upper and middle crust related to fluid circulation along both sediments and faults were detected the conductors in the upper crust coincide with the areal distribution of the cenozoic and mesozoic sedimentary rocks from the guadalquivir basin and the external betics and the conductors in the middle crust with the major miocene extensional detachments affecting the basement rocks of the internal betic zone a high conductivity zone at lower crustal levels beneath the outer internal betics was also detected next to an area where earlier seismic reflection data had imaged a duplication of the reflective moho this conductor was interpreted as partial melting of a southeast dipping subducted iberian lower crust the geodynamic significance of this subduction depends mainly on whether the overthrusting lower crust belongs to the alboran domain or to the iberian plate in the former case it would correspond to a major plate boundary and in the latter to an intraplate feature

electrical conductivity of magma in the course of crystallization controlled by their residual liquid composition 1 the electrical conductivity of a magma in the course of crystallization was experimentally investigated in the temperature range of 1350 1018 c large samples of basaltic composition with a homogeneous crystal content were synthesized in a gas mixing furnace at 1 atm pressure the samples were analyzed by electron microprobe the relative proportions of the phases as a function of temperature were determined depending on temperature the phase assemblies included quenched silicate liquid plagioclase pyroxene fe ti oxides the crystal content varied from 0 to 80 wt in response to partial crystallization the residual liquid changed composition from basalt to andesite to dacite liquid the electrical conductivity of the partially crystallized basaltic samples was measured in addition above liquidus conductivity measurements were conducted on compositions matching the residual liquid at different temperature these supplemental electrical measurements allowed us to discriminate the effect of crystal content from the effect of changing liquid composition associated with partial crystallization combining with the modified archie s law a set of constraints describing the conductivity of the residual liquid versus chemical composition and temperature we propose an equation to calculate changes in conductivity associated with partial magma crystallization we showed how the composition of the residual liquid is critical on the electrical behavior of crystal liquid system the model overcomes the previous difficulties in finding a robust model for describing the electrical behavior of crystal liquid systems the effect of liquid composition on the electrical conductivity is related to diffusion mechanisms and transport properties in molten silicate combining known constraints on na tracer diffusion and our conductivity results confirms the statements that sodium is the dominant charge carrier silicate liquids from basalt to rhyolite these findings revealed that we need a comprehensive model that can predict the conductivity of molten silicate as a function of chemical composition

on the link between the two modes of the ocean thermohaline circulation and the formation of global scale water masses a close link between the formation of global scale water masses such as north atlantic deep water nadw and antarctic intermediate water aaiw and two stable modes of the thermohaline circulation thc is investigated in a coupled model in the upper 2 3 km of the atlantic the thc modes are characterized by meridional overturning circulations of opposite sign with either a dominance of the aaiw cell over the nadw cell off thc mode or vice versa on thc mode a transition between these thc modes is controlled by the relationship between the densities in the source regions of formation of aaiw and nadw water masses this is shown by applying a freshwater perturbation in the region of enhanced aaiw formation in the southern ocean to obtain a hysteresis loop of the nadw circulation transitions between the two modes of the thc occur when the densities in the source regions of aaiw and nadw become comparable to each other

british ice sheet dynamics inferred from north atlantic ice rafted debris records spanning the last 175 000 years sediment core md04 2822 from the rockall trough northeast atlantic provides lithological evidence for the expansion of the british ice sheet bis onto the hebridean margin during both the penultimate marine isotope stage mis 6 wolstonian saalian and last glaciation devensian weichselian a composite chronology is constructed using i the benthic foraminiferal oxygen isotope record matched to an orbitally tuned stacked record of global ice volume specmap ii the synchronisation of the planktonic foraminiferal neogloboquadrina pachyderma sinistral and itrax xrf ca records to the greenland ice core ngrip back to ca 123 ka and iii the synchronisation of the same n pachyderma sinistral and itrax xrf ca records to the atmospheric methane record of the antarctic ice core epica dome c beyond 123 ka the first offshore evidence for the expansion of the last bis within mis 4 is presented suggesting extensive glaciation of northwestern britain during the devensian weichselian as early as 70 ka the proximity of this long sediment core to the glaciated margin of northwestern scotland makes it ideal to capture the ice rafted debris ird signal of the bis for the last 175 ka via a continuous flux record of ird british geological survey nerc 2009 all rights reserved

a robust multisite holocene history of drift ice off northern iceland implications for north atlantic climate an important indicator of holocene climate change is provided by evidence for variations in the extent of drift ice a proxy for drift ice in iceland waters is provided by the presence of quartz q

heat flow in the alboran sea western mediterranean abstract the results of the first regional heat flow survey carried out in the alboran basin are presented the survey consists of 98 heat flow measurements obtained using a violin type probe 697 nautic miles of gravity profiles 1446 nautic miles of bathymetric survey and 22 gravity cores a remarkable difference in heat flow patterns exists between the western wab and eastern eab parts of the alboran basin the average heat flow in the wab is 69 6 mw m 2 with a generally increasing trend towards the centre and to the east in contrast the heat flow pattern in the eab shows an average value of 124 8 mw m 2 and it is maintained rather constant for the overall area superimposed on this general pattern there are some local thermal anomalies associated with hydrothermal activity which have been detected in the central wab up to 123 mw m 2 in the south alboran basin sab up to 153 mw m 2 and in the djibouti bank db up to 254 mw m 2 after corrections for thermal refraction sedimentation and cooling of volcanic bodies the resulting heat flow distribution in the wab is smoother but still shows the increasing trend towards the centre and to the east in the eab the application of these corrections did not lead to any noticeable changes a 1 d approach that combines heat flow data crustal structure and elevation shows a dramatic decrease in lithospheric thickness from the wab 50 90 km to the eab 38 40 km likewise the resulting crustal thickness is around 14 16 km in the central part of the wab increasing towards the borders of the basin whereas in the eab the crustal thickness varies between 12 5 and 14 5 km in its western part and between 10 and 11 5 km in its eastern part

seasonal variability of the canary current a numerical study 1 a high resolution numerical model study of the canary basin in the northeast subtropical atlantic ocean is presented a long term climatological solution from the regional oceanic modeling system roms reveals mesoscale variability associated with the azores and canary current systems the northwest african coastal upwelling and the canary island archipelago the primary result concerns the canary current canc which in the solution transports 3 sv southward in line with observations the simulated canc has a well defined path with pronounced seasonal variability this variability is shown to be mediated by the westward passage of two large annually excited counterrotating anomalous structures that originate at the african coast the anomalies have a sea surface expression permitting their validation using altimetry and travel at the phase speed of baroclinic planetary rossby waves the role of nearshore wind stress curl variability as a generating mechanism for the anomalies is confirmed through a sensitivity experiment forced by low resolution winds the resulting circulation is weak in comparison to the base run but the propagating anomalies are still discernible so we cannot discount a further role in their generation being played by annual reversals of the large scale boundary flow that are known to occur along the african margin an additional sensitivity experiment where the azores current is removed by closing the strait of gibraltar presents the same anomalies and canc behavior as the base run suggesting that the canc is rather insensitive to upstream variability from the azores current

a multidisciplinary geophysical study in the betic chain southern iberia peninsula abstract the combined analysis of magnetotelluric measurements tomographic velocity models and deep seismic reflection images confirms that the betics orogen consists of the juxtaposition of two crustal domains characterized by distinctive physical properties at depth these data sets show evidence for a non coincidence of the petrological and the seismic moho beneath the betics chain the data sets reveal the geophysical properties of the alboran domain internal betics and the iberian massif external betics according to this the iberian crust features a relatively high seismic velocity is seismically transparent in the seismic reflection images and is electrically resistive the alboran domain crust is characterized by a low average velocity displays high reflectivity in the seismic reflection images and is electrically conductive the outcrops of the metamorphic complexes alpujarride and nevado filabride showing relatively high velocities coupled with low v p v s values 1 67 derived from the wadati slopes suggest the existence of rocks rich in silica beneath the alboran domain crust an interpreted detachment at 12 km depth imaged by deep seismic reflection suggests that these rocks could be related to the iberian upper crust partial melts and fluids are proposed to explain the high conductivity observed at deep crustal levels these would account also for the reflectivity and the low v p v s ratios mapped beneath the alboran domain

mid crustal detachment in the betic system of southeast spain abstract the tertiary orogenic belts of eastern spain can be interpreted using the principles of thin skinned thrusting with a fundamental detachment at mid crustal level in the eastern betics the compression involves an oblique restacking of a stretched continental margin much of the shortening is transmitted on permian and triassic detachments which emerge as forward and back thrust duplexes an interpretation of the guadarrama range of central spain is presented in which significant shortening is shown on a mid crustal detachment propagating from the southeast it is suggested that this represents the external limit of a compressive system linked to the betics the pyrenees and eastern cantabrians are a separate tertiary compressive system again resulting from restacking of an extensional basin during the collision of iberia and france previous authors have proposed mid crustal detachment in the pyrenees observation of the geological map of the iberian ranges suggests a broadly similar structural origin may apply in which case the iberian ranges may represent the most external zone of a major pyrenean system again linked by a mid crustal detachment thus it is suggested that the whole of eastern spain is made up of two major compressive systems linked at mid crustal level

the canary basin contribution to the seasonal cycle of the atlantic meridional overturning circulation at 26 n this study examines the seasonal cycle of the atlantic meridional overturning circulation amoc and its eastern boundary contributions the cycle has a magnitude of 6 sv as measured by the rapid mocha wbts project array at 26 n which is driven largely by the eastern boundary the eastern boundary variations are explored in the context of the regional circulation around the canary islands there is a 3 month lag between maximum wind forcing and the largest eastern boundary transports which is explained in terms of a model for rossby wave generated at the eastern boundary two dynamic processes take place through the lanzarote passage lp in fall the recirculation of the canary current and the northward flow of the intermediate poleward undercurrent in contrast during the remaining seasons the transport through the lp is southward due to the canary upwelling current these processes are linked to the seasonal cycle of the amoc

tracing time in the ocean a brief review of chronological constraints 60 8 kyr on north atlantic marine event based stratigraphies abstract well resolved event based stratigraphies in marine sediments spanning a significant portion of the last glacial period 60 8 kyr provide a unique opportunity for time stratigraphic correlation in the north atlantic region here we review the current methods available to chronologically constrain these event based stratigraphies highlighting in particular the value of tephrochronology as an independent tool to validate correlations between records while the intimate protocols lowe et al 2008 blockley et al 2011 are equally applicable to marine and terrestrial records spatially and temporally variable marine radiocarbon reservoir age effects mres provide a challenge to using marine radiocarbon in the former as an independent chronostratigraphic tool despite the inherent uncertainties associated with tuning we conclude that the mid points of the common abrupt warming transitions associated with the well defined millennial scale climate oscillations the dansgaard oeschger d o cycles observed in the oxygen isotopes of the greenland ice cores and north atlantic sea surface temperature sst records currently provide the most robust correlation tie points from which to derive age control in this invited intimate special issue article we propose a new protocol for establishing marine event based chronostratigraphies in the north atlantic region and focus on areas of chronological potential in palaeoceanographic research

on the mediterranean water composition abstractthe mediterranean outflow water mow spills from the mediterranean sea east north atlantic basin west off the strait of gibraltar as mow outflows it entrains eastern north atlantic central waters enacw and intermediate waters to form the neutrally buoyant mediterranean water mw that can be traced over the entire north atlantic basin its high salinity content influences the thermohaline properties of the intermediate deep water column in the north atlantic and its dynamics here the composition of mw in its source region the gulf of cadiz west off strait of gibraltar is investigated on the basis of an optimum multiparameter analysis the results obtained indicate that mixing of mow 34 1 0 3 occurs mainly with overlying enacw 57 1 0 8 in a process broadly known as central water entrainment a diluted form 80 of dilution of the antarctic intermediate water aaiw reaches the region and also takes part in mw formation 8 3 0 5 finally the underlying labrador sea wat

effect of partial melting on vp and vs in crustal enclaves from mazarron se spain abstract the combination of compressional and shear wave velocity is an important tool in discriminating rock types and identifying residing melts within the continental crust here we report the laboratory measurements for vp and vs obtained in varying conditions up to those exceeding the beginning of melting 950 c at 500 mpa confining pressure on two residual garnet biotite sillimanite cordierite spinel metapelitic enclaves recovered from the neogene dacites of mazarron se spain the enclaves preserve widespread interstitial rhyolitic glass as evidence of primary melt extraction at 500 mpa the experimental vp ranges from 7 21 7 46 km s 1 at room temperature to 5 44 km s at 950 c the mean vs is 4 5 km s at room temperature with shear wave splitting of 0 25 0 3 km s measured along three mutually orthogonal directions when temperature increases the vs evidences a reversible slope change at about 650 c and the shear wave splitting reduces to zero isotropic material at 850 950 c where the sample vs is 3 0 km s the vp anisotropy is 7 10 up to 700 c increasing to 20 at 950 c while the vs anisotropy continuously decreases with temperature from 5 to 7 at room temperature to zero at 950 c no mineral reactions are observed up to 650 700 c however microstructure equilibrates due to the relaxation of the primary glass at the glass transition temperature between 850 c and 950 c a new melting reaction is observed producing biotite spinel ilmenite plagioclase melt at melting the rock becomes isotropic for vs and poisson s ratio increases to 0 30 our seismic data show that the seismic signature of high grade metapelitic rocks is similar to that of mafic materials the evolution of vp and vs at melting conditions is compatible with the geophysical data of the area supporting the hypothesis of the current existence of anatectic melts at intermediate depths of the alboran domain

the vertical structure of upper ocean variability at the porcupine abyssal plain during 2012 2013 this study presents the characterization of variability in temperature salinity and oxygen concentration including the vertical structure of the variability in the upper 1000 m of the ocean over a full year in the northeast atlantic continuously profiling ocean gliders with vertical resolution between 0 5 and 1 m provide more information on temporal variability throughout the water column than time series from moorings with sensors at a limited number of fixed depths the heat salt and dissolved oxygen content are quantified at each depth while the near surface heat content is consistent with the net surface heat flux heat content of the deeper layers is driven by gyre scale water mass changes below 150m heat and salt content display intraseasonal variability which has not been resolved by previous studies a mode 1 baroclinic internal tide is detected as a peak in the power spectra of water mass properties the depth of minimum variability is at 415m for both temperature and salinity but this is a depth of high variability for oxygen concentration the deep variability is dominated by the intermittent appearance of mediterranean water which shows evidence of filamentation susceptibility to salt fingering occurs throughout much of the water column for much of the year between about 700 900 m the water column is susceptible to diffusive layering particularly when mediterranean water is present this unique ability to resolve both high vertical and temporal variability highlights the importance of intraseasonal variability in upper ocean heat and salt content variations that may be aliased by traditional observing techniques

resistivity structure of the olympic mountains and puget lowlands magnetotellurics has been used to study of the geo electric structure of the olympic mountains and puget lowland data were collected along an west east line extending from the pacific ocean to the cascade mountains the smoothest resistivity model consistent with the data suggests that subduction of the olympic mountains accretionary complex core rocks has been prevented by a 30 km thick sequence of volcanic rocks this may effectively couple the juan de fuca and north american plates and may explain the concentration of crustal earthquakes beneath the puget lowland

crustal resistivity structure of the southwestern transect of the rif cordillera morocco a ne sw magnetotelluric 110 km long profile including 18 sites was acquired across the western rifcordillera along the eurasian african plate boundary allowing to constrain its poorly known deepstructure it extends from the internal zones close to the alboran coast crossing the external zones andup to the gharb foreland basin the periods recorded range from 0 001 s to 1000 s the combination ofmagnetotelluric data with available geological data provides new insight regarding the relationship

northward penetration of antarctic intermediate water off northwest africa abstract in this article historical and climatological datasets are used to investigate the seasonal northward propagation of antarctic intermediate waters aaiw along the eastern margin of the north atlantic subtropical gyre a cluster analysis for data north of 26 n shows the presence of a substantial number of hydrographic stations with aaiw characteristics that stretch northeast along the african slope this water mass extends north during fall as shown both through the comparison of actual and climatological data and by applying a mixing analysis to normal to shore seasonal sections at both 28 5 and 32 n the mixing analysis is further used with several fall cruises between 32 and 36 n and shows that at these latitudes the core of aaiw propagates along the 27 5 isoneutral with contributions that reach as much as 50 at 32 5 n an idealized sverdrup type model is used in combination with climatological hydrographic and wind data to examine what forces this eastern boundary propagation it is fo

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

sofar float observations of an intermediate depth eastern boundary current and mesoscale variability in the eastern tropical atlantic ocean two neutrally buoyant sofar floats vigorously looped and meandered at depths of 950 1150 m in the eastern tropical atlantic ocean the float trajectories illustrate a poleward flow along the tropical eastern boundary and significant intermediate depth mesoscale variability in the low latitude eastern basin one float caught within an energetic cyclonic eddy near the eastern boundary looped cyclonically 14 times while translating 600 km northward parallel to the african coastline a second float launched near the mid atlantic ridge meandered eastward with a lagrangian zonal wavelength of 400 km and meridional amplitude exceeding 200 km satellite infrared imagery indicates that horizontal shear associated with the system of near surface zonal equatorial currents may contribute to the observed intermediate depth variability

a deep seismic reflection survey across the betic chain southern spain first results abstract two land seismic reflection profiles across the betic chain have imaged the deep structure of the crust belonging to two different crustal domains to the north one profile samples the crust of the variscan iberian massif that underlies the sedimentary cover of both the guadalquivir foreland basin and the south iberian crustal domain the upper crust is non reflective along the profile but the lower crust is reflective in the northern half of the profile between 7 and 12 s two way travel time in this segment of the profile the mono is also well imaged the quality of the data diminishes significantly as the profile enters the neogene guadix baza basin a second profile crossing the alpine metamorphic complexes of the betics reveals a reflective lower crust and a conspicuous reflection in the upper crust that is continuous for about 10 km at 11 s a distinct reflection has been interpreted as the reflection moho deeper reflections are also seen in the central part of the profile in a segment about 10 km long comparison with available refraction and wide angle reflection data shows some differences in both the crustal configuration and in the depth to the moho

interannual variability of antarctic intermediate water in the tropical north atlantic interannual variability of antarctic intermediate water aaiw in the tropical north atlantic is investigated using the gecco2 ocean state estimate and argo data aaiw salinity variability near the western boundary is highly correlated with the transport along the western boundary on interannual timescales northward propagating anomalies are associated with the western boundary transport variability that to some extent is related to the large scale wind stress curl forcing by means of the sverdrup balance aaiw anomalies also propagate westward with the speed of baroclinic rossby waves indicating that the displacement of the meridional salinity gradient by westward propagation of baroclinic rossby waves plays a role in the variability of aaiw characteristics slower eastward spreading of aaiw anomalies is identified on decadal timescales likely associated with the advection of salinity anomalies by weak eastward current bands understanding the observed interannual and decadal variability of aaiw salinity is important to properly interpret salinity changes reported in response to changes in the hydrological cycle

quasi synoptic transport budgets and water mass transformation in the azores gibraltar strait region during summer 2009 abstract we describe the circulation patterns in the azores gibraltar strait region north eastern atlantic during the 2009 caibox cruise on the basis of hydrographic and direct current velocity measurements this study offers new data for a region where importation of central waters subpolar and subtropical modes of eastern north atlantic central water and exports of mediterranean water are strongly related to large scale dynamics in the north atlantic ocean azores current mediterranean water system the description is backed up quantitatively by the results of a box inverse model which was used to obtain absolute water mass transport values consistent with thermal wind equations and with conservation of volume salt and heat the contributions of water masses were determined in an extended optimum multiparameter analysis from a quasi synoptic point of view providing detail in addition to volume salt and heat transport the surface subsurface large scale current system in the region consists of the azores current 13 1 2 5 sverdrup sv 1 sv 10 6 m 3 s 1 the azores counter current 5 2 2 1 sv the portugal current 4 5 1 4 sv and the canary current 7 1 1 1 sv broadly speaking central waters are imported into the caibox region at a rate of 1 6 0 9 sv and mediterranean water is exported at a rate of 1 5 0 4 sv the downwelling of central waters west of gibraltar strait was quantified at 1 1 sv not all this volume participates in mw formation but 0 8 sv of entrained central waters of which 0 5 sv are from central waters of subpolar origin and 0 3 sv from subtropical central waters of the 4 9 sv of subtropical central waters advected by the azores current about 0 7 sv would reach the gulf of cadiz region either to take part in central water entrainment or to flow across the gibraltar strait as part of the atlantic inflow to the mediterranean sea

the structure of holocene climate change in mid latitude north america abstract a sequence of long term and rapid changes during the holocene appears in a network of 40 well resolved paleoclimate datasets from mid latitude north america including records of pollen inferred temperatures alkenone derived sea surface temperatures ssts lake level changes dust accumulation and lake isotopes from idaho to maine statistical analyses reveal that changes in insolation and the laurentide ice sheet explain 51 7 of the variance in the records especially multi millennial trends but peak rates of change indicate additional rapid changes at ca 10 8 9 4 8 3 7 0 5 5 5 2 4 7 2 1 and 0 9 ka step changes between 9 4 and 8 3 ka relate to ice sheet dynamics that warmed much of the region and changes at 5 5 ka were the largest since the demise of the ice sheet the shift at 5 5 ka initiated widespread cooling and increases in effective moisture which culminated in the coolest wettest millennia in most areas after 2 1 ka replicated evidence from multiple records also shows a spatially varied set of multi century fluctuations including 1 low temperatures and high effective moisture at 5 5 4 8 ka in the mid continent and 2 repeated phases of low ssts cool summers and drought superimposed upon long cooling moistening trends in eastern north american since 5 5 ka

seismic signature of intracrustal magmatic intrusions in the eastern betics internal zone se iberia 1 receiver functions at three broad band stations located in the most easterly inner betics have been analyzed to investigate the structure of its underlying crust and uppermost mantle these stations are located within a geologically distinctive block bounded by the palomares alhama de murcia faults which is characterized by high heat flow values widespread strike slip faulting and neogene volcanism our analysis shows that a low velocity zone pervades the uppermost mantle beneath the stations and that the overlying crust has a high vp vs ratio and a prominent intracrustal low velocity zone i between the palomares and alhama de murcia faults and ii east of murcia perhaps thermally perturbing the upper crust north and east of cartagena independent studies show that the seismic velocities of the intervening mantle lid are normal beneath the stations and we suggest that our observations result from rapidly ascending magma diapirs ponding at intracrustal levels within the distinctive block

meddies and decadal changes at the azores front from 1980 to 2000 twenty years of time series observations from the deep sea mooring kiel276 are used to obtain information on the frequency and propagation of meddies mediterranean water eddies on long term changes in flow properties and on a possible relation to the north atlantic oscillation the mooring was set at the nominal position 33 n 22 w at a water depth of more than 5200 m in the northern canary basin it is located near the southern boundary of the azores current ac which is part of the north atlantic subtropical gyre and also in the large scale mediterranean water mw tongue originating from the strait of gibraltar the amplitudes of time varying vertical quasi geostrophic modes and the correlation of current and temperature changes at levels in the mw and the north atlantic central water above are used to identify meddies a total of 10 meddies passed the mooring during the period 1980 2000 half of the events can be related to earlier observations directional changes in meddy related velocities are used to estimate speeds and directions of meddy propagation directions of propagation are very homogeneous with all the 10 meddies observed propagating with a southward velocity component within a sector of 90 and typical speeds are 2 3 cm s meddy occurrence was uneven in time with six meddies found during the first four years and only four meddies during the remaining 16 years decadal changes show the annual mean and the fluctuating kinetic energy levels at the site changing from lower values in the 1980s to high values in the 1990s this change appears to be correlated with variations in the north atlantic oscillation nao index with a delay in oceanic response of about 3 years a conceptual model of ac meanders is used to identify meander signals in the upper layer time series the ac axis appears to be closer to the site during the 1990s than during the preceding decade and indicates a southward or southwestward displacement of the ac with increasingly positive values of the nao index meddy frequency is lower when the ac gets closer from the north a reduction in meddy occurrence in the region just south of the ac is possibly caused by the shear induced blocking of some meddies crossing the front from the north

meridional overturning transports at 7 5n and 24 5n in the atlantic ocean during 1992 93 and 2010 11 abstract transatlantic hydrographic sections along latitudes 7 5n and 24 5n have been repeated with about 20 years difference at the beginning of the 1990s and 2010s for each period an inverse model is applied to the closed box bound by both sections the model imposes mass conservation for individual layers defined by isoneutral surfaces and the whole water column using surface ekman transport and several transport constraints for specific ranges of longitudes and depths as a result the velocities at the reference layer for each station pair and the dianeutral velocities between layers are estimated and the horizontal velocity fields and the water heat and freshwater transports are calculated in particular we find that mass transport per stratum at 24 5n in 2011 is in good agreement with the transport estimates from the rapid watch array during both realizations the dianeutral velocities downwell from the upper north atlantic deep water unadw to the lower north atlantic deep water lnadw strata resulting in the merging of the two southward flowing strata at 24 5n into one deep southward moving stratum at 7 5n at 24 5n there is an increase in southward unadw transport between 1992 and 2011 compensated by a decrease of southward lnadw transport a descent in the upper limit of the antarctic bottom water aabw from 1992 to 2011 is also inferred the atlantic meridional overturning circulation amoc is larger in 1992 93 than in 2010 11 decreasing from 24 7 1 7 to 20 1 1 4 sv at 24 5n and from 29 2 1 7 to 16 9 1 5 sv at 7 5n much of this decrease arises because of the northward flow of antarctic intermediate water aaiw which was much more intense in 1992 93 than in 2010 11 as a consequence heat transport at 24 5n is not significantly different in 1992 1 4 0 1 pw and 2011 1 2 0 1 pw the estimation of heat transport at 7 5n strongly depends on the magnitude of the north brazil current over the american continental platform the freshwater flux into the box bounded by the two transoceanic sections decreases significantly from 1992 93 0 45 0 05 sv to 2010 11 0 36 0 3 sv meaning a decrease in net evaporation over this same area

nine years of mass transport data in the eastern boundary of the north atlantic subtropical gyre 1 one of the longest current meter time series in the lanzarote passage in the eastern boundary of the north atlantic subtropical gyre has been used to determine and quantify the 9 year mean transport the inter annual and seasonal mass transport variability for the three water masses present in the area results show north atlantic central water nacw flowing southward in the upper levels with a mean mass transport of 0 81 1 48 sv antarctic intermediate water aaiw flowing northward at intermediate levels with a mean transport of 0 09 0 57 sv and mediterranean water mw flowing southward in the deep part of the passage with a mean transport of 0 05 0 17 sv harmonic and wavelet analysis show the presence of a seasonal pattern in the passage for the three water masses a maximum southward transport in winter and spring has been observed for the nacw followed by a minimum in summer and fall near zero values during winter and spring are found for aaiw with a maximum northward value in summer and a negative value in fall when this water mass reverses its flow mw has a similar seasonal pattern to nacw the vertical structure in the lanzarote passage can be approximated by four significant oscillatory modes which cumulatively explain 86 4 of the variance the strong transport fluctuation found at the seasonal and inter annual timescales demonstrates that the eastern boundary current transport has a strong impact on meridional overturning estimates thus indicating that to understand meridional overturning circulation variability these transport estimates at the eastern atlantic margin are necessary

stable isotope stratigraphy of the pliocene pleistocene climate transition in the northwestern subtropical pacific abstract from ocean drilling program odp site 1208 on shatsky rise below the kuroshio current extension we present the north pacific s first orbital scale benthic foraminiferal 18o and 13c time series to span the pliocene pleistocene climate transition excellent agreement between the site 1208 18o record and the global 18o stack of lisiecki and raymo 2005 provides orbital scale age control and confirms continuous stratigraphy from 3 7 to 1 8 ma at the single hole site cross spectral analysis of the 18o and 13c time series reveals that these are coherent to 80 confidence at the 41 kyr obliquity band prior to 3 3 ma glacial isotope stage m2 and increase to the 95 level thereafter throughout 18o cycles consistently lead 13c cycles by 3 kyr this suggests that global ocean 13c variations as produced by terrestrial marine 12c transfers were responsive to obliquity induced climate changes before the northern hemisphere glaciations nhg reached mid latitudes at 2 7 ma in contrast 41 kyr carbonate sedimentation as derived from sediment reflectance cycles maxima tightly coupled to 95 confidence and in phase with minima in the 18o record do not emerge until 2 7 ma foraminiferal fragmentation counts indicate that carbonate preservation is not the primary process behind enhanced carbonate deposition during interglacials thus we surmise that hydrography related changes in biogenic opal and carbonate production in surface water best explain glacial interglacial carbonate cycles beginning with significant nhg firm establishment of orbital scale age control on the stratigraphically complete site 1208 section now provides a platform for high resolution paleoceanographic reconstruction of the relatively understudied north pacific