the mesozoic and tertiary basins of the bohemian massif and their evolution abstract the bohemian massif is a major positive element within the structural framework of the alpine carpathian foreland its basement became consolidated during the variscan orogeny crustal thicknesses range between 32 5 km and 40 km during the late carboniferous and early permian the bohemian massif became dissected by a conjugate system of wrench faults which controlled the accumulation of a continental coal bearing series late permian red beds were deposited on intramontane topographic depressions in triassic to mid jurassic times the bohemian massif formed a high from which clastics were shed into adjacent basins during the late jurassic and late cretaceous it became transected by nw se trending sedimentary basins the sub hercynian and laramide phases of foreland compression resulted in deformation and uplift of the bohemian massif the eger graben a 350 km long volcanotectonic zone cutting across the bohemian massif in an ene wsw direction came into evidence during the oligocene and is at present inactive the crust of the bohemian massif forms the autochthonous substratum of the outer carpathians which are paralleled by the neogene carpathian foredeep the neogene intramontane neo autochthonous vienna basin is superimposed on the alpine carpathian nappe systems and developed under a tensional setting

anomalous temperature and salinity variations in the tropical atlantic possible causes and implications for the use of altimeter data near real time subsurface observations at a pirata mooring in the western equatorial atlantic show a temperature and salinity drop in boreal spring 1999 which is consistent with a 60 m upward shift of the thermocline at the same time sea level observations from topex poseidon and ers 1 2 show anomalously low values over a large part of the tropical atlantic north of the equator the sea level observations are also used to correct for errors in upper ocean heat content in a global ocean analysis which is used to initialize seasonal forecasts it is shown that the ability of altimeter data to reproduce observed temperature changes is limited in the western equatorial atlantic this may partly be because large temperature changes occur very rapidly but is mainly because strong salinity variations compensate up to 10 cm of the sea level signal from temperature

on the seasonal cycle of the equatorial atlantic ocean abstract although the seasonal cycle of the equatorial atlantic and pacific oceans have many similarities for example an annual signal is dominant at the equator even though the sun crosses the equator twice a year different processes determine the seasonal cycles of the two oceans and in the atlantic different processes are important in the east and west in the gulf of guinea in the eastern equatorial atlantic the seasonal cycle of surface winds is primarily in response to seasonal variations in land temperatures so that annual changes in sea surface temperatures are to a first approximation the passive response of the ocean to the winds the seasonal cycle of the western equatorial atlantic has similarities with that of the equatorial pacific both are strongly influenced by ocean atmosphere interactions in which the surface winds and sea surface temperature patterns depend on each other but only in the western equatorial atlantic are the seasonal variations in sea surface temperature influenced

the establishment of a pelagic sargassum population in the tropical atlantic biological consequences of a basin scale long distance dispersal event abstract starting in 2011 coastal areas of the caribbean sea and tropical atlantic ocean began to experience extraordinary yearly accumulations of pelagic sargassum brown alga historical reports place large quantities of sargassum only in the north atlantic mostly in the gulf of mexico and the sargasso sea accumulations of sargassum in the tropical atlantic have continued we used a numerical particle tracking system wind and current reanalysis data drifting buoy trajectories and satellite imagery to determine the origin of the sargassum that is now found persistently in the tropical atlantic our analyses suggest that during the extreme negative phase of the winter 2009 2010 north atlantic oscillation nao unusually strong and southward shifted westerly winds explain the transport of sargassum from the sargasso sea 20 40 n 80 20 w into the far eastern north atlantic our hindcast sargassum distributions agree with surface current simulations with the inclusion of windage windage is the additional wind induced drift of material floating at the free surface resulting from direct wind forcing on the sea surface as well as on floating or partially submerged objects in our simulations windage is included as an added vector speed and direction to the model computed surface ocean currents equivalent to 1 of surface wind velocities lagrangian analysis of the regional circulation suggests that 1 part of the sargassum subsequently drifted to the southwest in the north equatorial current nec and entered the central tropical atlantic arriving in the caribbean by the spring of 2011 with 2 another portion continuing southward along the coast of africa in the canary current eventually joining the seasonally varying system of tropical atlantic currents and thereby delivering a large sargassum population to the tropical atlantic since then sargassum patches aggregate from march to september in massive windrows along the inter tropical convergence zone itcz under the action of converging winds the windrows follow the itcz in its seasonal northward migration in the central tropical atlantic they are stretched across the central tropical atlantic as the itcz crosses the latitude of the seasonal formation of the north equatorial counter current necc these patches and windrows are exposed to high sunlight and open ocean upward flux of nutrients due to eddy and wind driven mixing in the central tropical atlantic during the northern spring and summer as the sargassum drifts farther north with the itcz large portions of the population are advected into the eastern caribbean sea some of these patches remain dispersed as the itcz migrates southward and re aggregate into new windrows as the itcz intensifies the following march april if wind mixing is strong and the mixed layer is deeper than about 50 60 m in the southern tropical atlantic at this time the sargassum will bloom and form a massive windrow otherwise the bloom will be inhibited the extreme 2009 2010 nao wind anomaly could be considered as triggering a biosphere tipping point that caused important ocean scale ecosystem changes in the tropical atlantic with significant recurrent social and economic consequences understanding whether this new expanded geographic range of massive sargassum blooms is temporary or whether it will revert to its pre 2009 distribution requires sustained monitoring and research

evolution of the lower saxony basin abstract the lower saxony basin is a 300 km long and 65 km wide late jurassic and early cretaceous trough which parallels the northern margin of the rhenish massif this basin became inverted during the senonian and paleocene the lower saxony basin is the most important oil province of germany past production amounts to 200 10 6 t of oil 1 5 10 9 bbl the lower saxony basin is superimposed on the late carboniferous variscan foredeep basin and the frontal structures of the variscan fold belt during the permian to middle jurassic the area formed part of the northwest european basin differential subsidence of the lower saxony basin was initiated during the late jurassic and persisted till albian time this involved reactivation of permo carboniferous fracture systems by divergent wrenching a major aptian deep seated laccolith is evident in the western part of the lower saxony basin during the senonian and paleocene sinistral convergent wrenching induced uplift of the basin floor and folding of its sedimentary fill the margins of the inverted lower saxony basin are thrust over the adjacent stable platform areas the differential subsidence of the lower saxony basin can be related to a period of major crustal extension in the north sea rift basin inversion coincides with important orogenic events in the alpine system and is thought to have been induced by intra plate compressional stresses

crustal fracturing and intraplate tectonics in the area between the north sea and the alps a comparison of landsat derived fractures with existing map data abstract after a short review of late permian to recent structural development in the area between the north sea and the alps known major faults and fault systems and their role in intraplate tectonics are discussed it is shown that landsat derived trends and patterns of upper crustal fracturing correlate with known regional and local fault patterns and that pre existing trends and patterns of crustal fracturing have played a major role in late permian to recent intraplate deformation

tropical atlantic seasonal dynamics in the early middle eocene from stable oxygen and carbon isotope profiles of mollusk shells there are disagreements whether the tropical sea surface temperature during the warm early to early middle eocene was equal to the present temperature or significantly lower in order to determine the sea surface temperature of the eastern tropical atlantic in the early middle eocene we have established 18o and 13c profiles along the transect of growth of excellently preserved shells of turritella gastropods and a macoma bivalve from tropical west africa this method makes possible a distinction between the winter and the summer temperature the 18o and 13c data indicate sea surface temperatures of 29 31 c which declined to 23 25 c during seasonal upwelling these conditions are similar to those of today and suggest that significant seasonal dynamics prevailed in the early middle eocene tropics the new data further contradict that the tropics cooled during the generally warm early to early middle eocene as inferred in studies on foraminifera 18o

evidence for active tilting of the nw german basin from correlations between fluvial landscape and geological subground the catchment basin of the river hunte lower saxony nw german basin was studied on a mesoscale length of 90 km to investigate the influence of the geological subground on modern morphology a geo information system gis was used to calculate linear correlation coefficients between the depth of geological strata base zechstein to base quaternary and the height of the modern landscape holocene alluvial plain lower weichselian terrace catchment basin and watershed high linear correlation coefficients between the base of tertiary and the height of the modern topography catchment basin r2 0 87 lower weichselian terrace r2 0 95 and holocene alluvial plain r2 0 95 indicate control of the modern topography by the depth of the geological subsurface via tilting of the entire basin most likely northward tilting of the nw german basin forces the river hunte to flow in a northerly direction by relative uplift of the hinterland wiehengebirge rhenish massif and subsidence of the north sea area

late cretaceous and cenozoic intra plate compressional deformations in the alpine foreland a geodynamic model abstract the mesozoic grabens and wrench induced troughs of western and central europe developed in response to triassic early cretaceous intra plate tensional stresses which affected the arctic north atlantic and the tethys borderlands during the rifting phase preceding the opening of the respective oceans this resulted in the fragmentation of the continental crust of the alpine foreland during the late cretaceous and tertiary alpine orogeny collision related compressive stresses exerted on the foreland induced the reactivation of these fracture systems causing the inversion of mesozoic grabens and the uplifting of major basement blocks at distances up to 1300 km to the north of the present alpine deformation front the structural style of these inverted basins and basement uplifts is indicative of compressional and transpressional deformations the total amount of crustal shortening associated with these deformations is unlikely to exceed a few tens of kilometres these displacements require a coupling between the foreland and the orogen at the alpine a subduction zones and within the foreland a decoupling at intra crustal levels between the crust and mantle and or at deeper lithospheric levels the example of the alpine foreland indicates that compressive stresses inducing major deformations can be transmitted from a collisional plate boundary through continental lithosphere over distances of up to 1300 km circumstantial evidence suggests that collision related compressive stresses not large enough to give rise to significant deformations can be transmitted through continental lithosphere over even greater distances

unraveling multiple thermotectonic events accommodated by crustal scale faults in northern iberia spain insights from k ar dating of clay gouges

evolution of the molasse basin germany switzerland abstract in the molasse basin 500 1000 m thick mesozoic sediments overlie the variscan basement and locally permo carboniferous grabens containing a largely unknown thickness of clastic sediments the vindelician basement high extended southwestward from the bohemian massif and separated the southern part of the german basin from the tethys shelf triassic early and middle jurassic sediments progressively transgressed over this high which became fully inundated during the late jurassic following a temporary regression sedimentation resumed in the early cretaceous and after another hiatus in the late aptian to campanian during the latest cretaceous to earliest tertiary the area of southern germany became uplifted resulting in a progressive northwestward truncation of cretaceous strata and the late jurassic carbonates at the same time the bohemian massif became upthrusted along northwest striking wrench faults similar faults controlled the upthrusting of the landshut neuoetting high over which some 1 000 m of mesozoic sediments were eroded these wrench and thrust tectonics are part of an extensive compressional deformation in central europe that is supposed to be caused by the latest cretaceous earliest tertiary collision of the adriatic african and european plates during the alpine orogeny the area subsided again during the late eocene and developed into the molasse basin proper in which oligocene to miocene elastics reach a thickness of some 5 000 m near the alpine thrust front subduction and flexuring of the foreland caused numerous essentially basin parallel synthetic and antithetic normal faults the latter form the primary traps for oil and gas accumulations in the molasse basin

the mean and annual cycle of upper layer temperature fields in relation to sverdrup dynamics within the gyres of the atlantic ocean using 28 years of expendable bathythermograph data 1967 1994 we describe the mean and annual cycle of the upper ocean temperature fields in the atlantic from 30 s to 50 n in the context of the basin scale wind driven gyres sverdrup stream function field which provide a framework for describing the oceanographic measurements we examine the circulation field implied by the temperature distributions which are used as a proxy for the field of mass similarities between the temperature and stream function fields increase with depth in the lower to subthermocline depths of the tropical and equatorial gyres the zonal currents form a closed circulation a southeastward boundary current is suggested near and below 150 m that provides closure for the tropical gyre and the equatorial gyre axis is southward of that suggested by the stream function field higher in the water column the north equatorial countercurrent necc may be a surface manifestation of the north equatorial undercurrent neuc where the latter can be interpreted as the southern limb of the tropical gyre because there are large vertical shears in the tropics the equatorial gyre is not clearly indicated in the vertically integrated temperature field but appears below about 200 m here the south equatorial undercurrent seuc can be interpreted as the eastward flowing northern limb of the equatorial gyre and is opposite in direction to the westward flowing south equatorial current above both the neuc and seuc are analagous to currents in the pacific that are governed by non sverdrup dynamics despite the shortcomings of the data the mean annual cycle appears to be relatively stable and we have discounted the possibility that in regions where it represents a significant percentage of the total variance it is changing slowly over the 28 years of record the wind forcing fields which undergo large meridional movements 5 6 of latitude during their annual cycle with some exceptions have essentially no counterpart in gyre movements between their seasonal extremes most of the variability associated with the annual cycle is confined to the upper 300 m greatest variability where ranges exceed 6 c occurs in the northwestern atlantic in late winter and early spring during this time of year south of the gulf stream and below about 100 m water temperatures exhibit a systematic phase lag with depth the next largest area of variability where ranges can also exceed 6 c resides in the tropical western basin between the equator and 10 n just below 100 m in the eastern basin ranges decrease and shoal additionally the phase fields are consistent with the intensification and relaxation of the tropical ridge trough system where the necc disappears in march in the west but the necc neuc complex is strongest in september

sensitivity of tropical atlantic climate to mixing in a coupled ocean atmosphere model the sensitivity of tropical atlantic climate to upper ocean mixing is investigated using an ocean only model and a coupled ocean atmosphere model the upper ocean thermal structure and associated atmospheric circulation prove to be strongly related to the strength of upper ocean mixing using the heat balance in the mixed layer it is shown that an excessively cold equatorial cold tongue can be attributed to entrainment flux at the base of the oceanic mixed layer that is too large enhanced entrainment efficiency acts to deepen the mixed layer and causes strong reduction in the upper ocean divergence in the central equatorial atlantic as a result the simulated sea surface temperature thermocline structure and upwelling velocities are close to the observed estimates in the coupled model the seasonal migration of the intertropical convergence zone itcz reduces when the entrainment efficiency in the oceanic mixed layer is enhanced the precipitation rates decrease in the equatorial region and increase along 10 n resulting in a more realistic atlantic marine itcz the reduced meridional surface temperature gradient in the eastern tropical atlantic prohibits the development of convective precipitation in the southeastern part of the tropical atlantic also the simulation of tropical atlantic variability as expressed in the meridional gradient mode and the eastern cold tongue mode improves when the entrainment efficiency is enhanced

the evolution of the south hunsruck and taunus borderzone abstract the main fabric development of the south hunsruck and taunus borderzone htb occurred during late variscan homoaxial backfolding of an early variscan stack of thrust sheets in a narrow wsw ene trending zone several hundred kilometres long rotation and uplift of the southern rhenohercynian zone was accompanied by the subsidence of the southward adjacent northernmost parts of the saxothuringian zone and the development of the saar nahe basin during the latest carboniferous changing stress conditions gave rise to the development of normal faults along the htb and an extensive tholeiitic and rhyolitic volcanism contemporaneous uplift of the hunsruck is reflected by coarse elastics in the saar nahe basin subsequently the htb became covered by latest carboniferous early permian and mesozoic sediments cretaceous uplift of the rhenish shield caused their erosion the faultzone separating the rhenohercynian hunsruck and taunus from the permo carboniferous saar nahe basin is characterised by reverse and normal faults conjugate shear indicated by slickensides on steep oblique fracture planes as well as slight folding and small scale thrusting in post variscan sediments may be attributed to compressional foreland deformation reactivating variscan joint fabrics and fault systems timing of these deformations is ambiguous and could partly be related to dextral shear during the cenozoic subsidence of the rhine graben cenozoic sediments of the upper rhine graben overstep the northeastern parts of the htb seismic investigations indicate that the htb is associated with a system of southeast hading listric planes extending beneath the moho occasional dip slip earthquakes occur along these fractures

seasonal propagation of sea level along the equator in the atlantic in the equatorial atlantic the sea surface height ssh anomaly field is dominated by an annual signal propagating eastward this signal has been previously interpreted in terms of propagating waves in this article it is argued that this propagating signal is not a free equatorial kelvin wave because the phase velocity observed is too small compared to first second or third baroclinic mode kelvin waves and is not the result of an equatorial forced wave because the zonal wind stress does not show a similar propagation rather it is suggested that the eastward propagation in ssh is due to the sum of two independent modes of variability one mainly driven by the wind stress curl off the equator and the other driven by the zonal wind stress along the equator these two modes are uncorrelated in time and space and therefore can be conveniently separated by an empirical orthogonal function analysis of the equatorial atlantic sea surface height the first mode explains 74 of the variance is one signed in longitude and is interpreted as the variability of the warm water volume above the thermocline the second mode explains 24 of the variance consists of an east west tilt along the equator and is driven by variations of the zonal equatorial wind stress

compressional intra plate deformations in the alpine foreland an introduction abstract the recognition of the basin inversion phenomenon dates back to the 1920 s and 1930 s the true scope of the latest cretaceous and cenozoic basin inversions became apparent only in the 1970 s it is proposed that these intra plate deformations are related to compressional stresses exerted on the foreland during the alpine orogeny

tropical instability waves at 0 n 23 w in the atlantic a case study using pilot research moored array in the tropical atlantic pirata mooring data temperature salinity velocity and wind from a mooring at 0 n 23 w are used along with satellite data for sea surface temperature and sea level to examine the contribution of tropical instability waves tiws to the energy and heat balance of the equatorial atlantic mixed layer the tiws appear as periodic 20 30 day fluctuations of currents temperature and salinity which intensify beginning in june and peak in late boreal summer the intensification occurs in phase with strengthening of the southeasterly trade winds and the seasonal appearance of the equatorial tongue of cold mixed layer temperatures in 2002 these waves which warm the mixed layer by 0 35 c during summer months are maintained by both barotropic and baroclinic conversions that are of comparable size salinity fluctuations previously neglected increase the magnitude of baroclinic energy conversion

interplay of plutonism and regional deformation in an obliquely convergent arc southern coast belt british columbia the coast plutonic complex is an extensive zone of continental growth that formed along the mesozoic convergent margin of northwestern north america the orogeny creating this belt involved terrane accretion and assembly massive upward transfer and emplacement of sial in the form of batholiths constituting a magmatic arc and transformation of broad tracts of sedimentary and volcanic rocks into crystalline continental crust all operating in more or less the same space and time the mechanisms and interplay of these orogenic processes are well displayed in the harrison lake area of the southern coast belt british columbia great structural relief across the area exhibits a present day architecture defined by thin thrust stacked terrane sheets and early concordant pluton sheets folded on a macroscopic scale all truncated by oblique dextral reverse faults and overlain by later floored plutons construction of this complex began with terrane assembly on orogen normal thrusts during a lull in plutonism in the early cretaceous low grade metamorphism during this event indicates only modest crustal thickening subsequent plutons intruded into the assembled terranes appear to be composites of sheets early pluton sheets are now steeply dipping due to folding but were likely intruded as horizontal bodies large ovoid post folding plutons are mostly subhorizontal floored bodies at least in part sheeted these plutons are underlain by barrovian mineralogic aureoles that indicate downward vertical displacement of 10 km or more during plutonism suggesting pluton emplacement by vertical inflation magmatic fabrics in these bodies and the discordant relation of plutons to regional structures preclude emplacement in active fault zones penetrative strain aureoles flanking plutons are mostly limited to zones a few hundred meters wide and regional tectonic structures are widely preserved tectonic deformation of the arc is characterized by contraction and strike slip not orogen normal extension plutons played a greater role than terrane accretion in causing crustal thickening and high grade metamorphism

plutonism oblique subduction and continental growth an example from the mesozoic of california major episodes of mesozoic plutonism in california correlate with periods of oblique subduction and trench parallel transport of western california along intrabatholithic faults major episodes of plutonism occurred in the late jurassic during left oblique convergence and in the mid cretaceous during right oblique convergence in contrast a conspicuous lull in plutonism but continuation of volcanism in the earliest cretaceous coincides with a time when the north america farallon convergence vector although large in magnitude was oriented perpendicular to the trench this correlation suggests that plutonism is facilitated by strike slip faulting within the batholithic belt one explanation which helps to solve the plutonic room problem is that plutons are passively emplaced at releasing bends in the strike slip faults and volume is conserved by thrusting at the trench if this correlation is generally applicable then it implies that mid crustal plutonism is limited beneath areas in which the convergence vector is subperpendicular to the trench continental growth in such areas may occur dominantly by volcanism

transition regions and their role in the relationship between sea surface height and subsurface temperature structure in the atlantic ocean expendable bathythermograph xbt profiles and topex poseidon altimeter data t p are compared for the years 1993 through 1997 to determine how much can be understood about water column variability from xbt s given only sea height anomalies sha from t p our focus is on the annual cycle along two well sampled xbt sections in the atlantic ocean from 10 s to 40 n regions of transition are identified that separate the mid latitudes where surface buoyancy fluxes dominate the forcing of sea level from those in the equatorial region where thermocline effects dominate zones of transition occur in the vicinity of troughs where small fluctuations in sha belie the true nature of water column variability here surface and thermocline variability tend to cancel each other thus the character of sha in transition regions emphasizes how important direct observations can be in interpreting satellite altimetric observations correctly when both surface and thermocline variability are important but are compensating in nature

compression and right lateral strike slip movement at the southern hunsruck borderfault southwest germany abstract compressional tectonic structures have been known from the southern hunsruck borderzone since the end of the last century in the western part of the borderzone the saar nahe syncline is upthrown whereas in the eastern part the hunsruck is upthrown against the saar nahe syncline folds with axes parallel and oblique to the 60 trending fault zone have been described in the past in the area between idar oberstein and kirn permian lava sheets are displaced in such a way that their recent distribution can be explained by a right lateral strike slip movement of 5 8 km the block of the saar nahe basin between the southern hunsruck borderfault and the saarbrucken anticline has been tilted to the ene since the late palaeozoic the transcurrent movement can only be related to the opening of the upper rhine graben ne sw and nne ssw trending folds in the rotliegend sediments are considered to be transpression structures related to strike slip movement in early tertiary times recent seismicity along the southern hunsruck borderzone indicates that this zone is still active

lagrangian sources of frontogenesis in the equatorial atlantic front estimating the processes that control the north equatorial sea surface temperature sst front on the northern edge of the cold tongue in the tropical atlantic is a key issue for understanding the dynamics of the oceanic equatorial atlantic and the west african monsoon diagnosis of the frontogenetic forcings on a realistic high resolution simulation was used to identify the processes involved in the formation and evolution of the equatorial sst front the turbulent forcing associated with the mixed layer turbulent heat flux was found to be systematically frontolytic while the dynamic forcing associated with currents was found to be frontogenetic for the equatorial sst front nevertheless the low frequency component of the turbulent forcing was frontogenetic and initiated the sst front which was then amplified and maintained by the leading dynamic forcing this forcing was mainly driven by the meridional convergence of the northern south equatorial current nsec and the guinea current which points out the essential role played by the circulation in the equatorial sst front evolution the quasi biweekly variability of the equatorial sst front and its forcings were found to be more strongly coupled to the wind energy flux wef than to the surface wind stress in fact the wef controlled the convergence divergence of the nsec and guinea current and thus the meridional component of the leading dynamic forcing the wef explains the equatorial sst front development better than the wind does because it is a coupled ocean atmosphere process

p t t evidence for mechanisms of vertical tectonic motion in a contractional orogen north western us and canadian cordillera the 1800 km long coast mountains north cascades orogen of the canadian cordillera and north western us developed as a continental magmatic arc metamorphic rocks in the orogen contain widespread evidence for burial of supracrustal rocks to depths of c 40 km followed by nearly isothermal decompression to depths of 10 km near many shallowly emplaced mid cretaceous plutons low pressure contact metamorphic effects were overprinted by high pressure regional metamorphic minerals and textures as evidenced by kyanite staurolite pseudomorphs after andalusite in metapelitic rocks therefore near pluton rocks record the loading history of the orogen metapelitic rocks not associated with plutons only preserve evidence for high pressure conditions and or high temperature decompression as indicated for example by sillimanite and cordierite after kyanite and garnet respectively petrological evidence for burial and decompression is therefore recorded in different rocks various regions of the orogen differ in timing of metamorphism the overall shape of p t paths and the relative timing and regional extent of the high pressure event but most of these data and observations are consistent with thrusting and or pure shear thickening as primary loading mechanisms throughout the orogen as opposed to magma dominated loading this interpretation is further supported by comparison with thermal models which demonstrate that the p t paths are consistent with simultaneous thrusting and folding at a high initial geothermal gradient 35 40 c km 1 in much of the orogen a high geothermal gradient supports tectonic models invoking intra arc contraction and suggests that magmatism played an important role in regional temperature time paths this tectonic thermal history may be typical of other contractional orogens and illustrates the importance of large vertical displacement of crust in magmatic arcs

tropical instability wave kinematics observations from the tropical instability wave experiment the kinematics of planetary waves originating from instability of the nearsurface equatorial currents are reported on using velocity measurements from an array of acoustic doppler current profilers deployed in the equatorial pacific during the tropical instability wave experiment a distinctive wave season was observed from august to december 1990 with wave energy confined primarily above the core of the equatorial undercurrent particle motions in the horizontal plane are described by eccentric ellipses oriented toward the north but tilting into the cyclonic shear of the south equatorial current the tilt is maximum near the surface just north of the equator and decreases to the south and with depth the distribution of wave variance is narrowband in both frequency and zonal wavenumber with central period zonal wavelength and westward directed phase propagation estimated to be 500 hours 1060 km and 59 cm s 1 respectively neither the meridional nor the vertical wavenumber component is statistically different from zero these results generally agree with previous findings on tropical instability waves from the atlantic and pacific oceans and in the undersampled arena of geophysical measurements they provide an example where statistical inference is supported by an ensemble of independent measurements

a description of the annual cycle in sea surface temperature and upper ocean heat in the equatorial atlantic abstract temperature and velocity time series obtained by surface moorings during the seasonal response of the equatorial atlantic experiment are used to investigate the role of ocean dynamics upon the annual cycle of equatorial sea surface temperature sst and upper ocean heat the annual cycle in sst is explained by different mechanisms each operant at different phases of the cycle the boreal springtime decrease in sst results from upwelling in response to the seasonal intensification of easterly wind stress this upwelling causes the seasonal formation of the cold tongue along the equator in the central and eastern portions of the basin an early summer increase in sst is attributed to the meridional convergence of reynolds heat flux associated with surface current instability generated waves after the instability waves abate sst and mixed layer depth remain relatively steady from late summer through fall when the advective terms are small and cancelling suggesting that surface heating is then

equatorial upwelling rates inferred from helium isotope data a novel approach 1 upwelling is one of the key processes to maintain the tropical atlantic cold tongue this feature is of special interest to climate research since its sst variability is significantly correlated with the west african monsoon direct measurements of the upwelling have been hampered by the small speeds involved instead vertical motion has to be estimated by indirect methods here we propose a novel approach to infer equatorial upwelling velocities by exploiting the helium isotope disequilibrium between atmosphere and equatorial oceanic mixed layer the data were collected during woce cruises a13 and a14 although the vertical and horizontal resolution of the helium data in the upper tropical oceans was too poor to support a detailed study it was sufficient to show the potential of the method

using multiple passive tracers to identify the importance of the north brazil undercurrent for atlantic cold tongue variability the use of multiple passive tracers in a dynamical ocean model is presented as a method to study water mass origins the multiple passive tracer method is successfully applied to determine the origin regions of the atlantic cold tongue act using 31 passive tracers at the time of the act minimum in sea surface temperature 38 3 of the surface water in the central equatorial atlantic is found to originate in the western side of the basin with only 11 2 originating in the east conversely for the act surface cooling off the west coast of africa only 2 1 is from the west of the atlantic basin with 71 7 from the east the region of the north brazil undercurrent is found to be the most important origin region for the central atlantic act region for a 6 8 month lead time using the met office en4 observational dataset of ocean temperatures correlations are found between january temperatures in the north brazil undercurrent region and both the act mean temperature and act spatial extent in july august significant at the 0 95 level this suggests that the 6 month lead time predictability of the act may be increased by improved knowledge of the north brazil undercurrent temperature results from previous studies suggest that such increased predictability of the act could potentially help improve predictions of the west african monsoon

satellite derived surface current divergence in relation to tropical atlantic sst and wind the relationships between tropical atlantic ocean surface currents and horizontal mass divergence sea surface temperature sst and winds on monthly to annual time scales are described for the time period from 1993 through 2003 surface horizontal mass divergence upwelling is calculated using surface currents estimated from satellite sea surface height surface vector wind and sst data with a quasi linear steadystate model geostrophic and ekman dynamical contributions are considered the satellite derived surface currents match climatological drifter and ship drift currents well and divergence patterns are consistent with the annual north south movement of the intertropical convergence zone itcz and equatorial cold tongue evolution while the zonal velocity component is strongest the meridional velocity component controls divergence along the equator and to the north beneath the itcz zonal velocity divergence is weaker but nonnegligible along the equator a strong divergence upwelling season in the central eastern equatorial atlantic peaks in may while equatorial sst is cooling within the cold tongue in addition a secondary weaker and shorter equatorial divergence occurs in november also coincident with a slight sst cooling the vertical transport at 30 m depth averaged across the equatorial atlantic ocean between 2 s and 2 n for the record length is 15 6 10 6 m 3 s 1 results are consistent with what is known about equatorial upwelling and cold tongue evolution and establish a new method for observing the tropical upper ocean relative to geostrophic and ekman dynamics at spatial and temporal coverage characteristic of satellite based observations

intraseasonal mixed layer heat budget in the equatorial atlantic during the cold tongue development in 2006 1 estimating the mixed layer heat budget is a key issue for understanding the cold tongue development in the eastern equatorial atlantic a high resolution ocean regional model is used to diagnose the mixed layer heat budget online during the egee 3 experiment from may to august 2006 the heat budget shows the major role of the horizontal advection and turbulent mixing in the mixed layer temperature balance in the cold tongue the surface net heat flux and entrainment processes play a minor role the equatorial cooling is mainly induced by low frequency advection which is balanced by high frequency zonal and meridional advections the high frequency advections are organized in patterns along the northern edge of the cold tongue where they are associated with strong sea surface temperature gradients and well developed tropical instability waves in the western atlantic special attention is paid to the wind energy flux which controls horizontal advection and turbulent mixing we suggest that the wind energy flux drives the vertical velocity which in turn adjusts the mixed layer depth its stratification and the vertical shear of the horizontal current although vertical advection is not essential in providing cold water in the atlantic cold tongue it is shown that the vertical velocity plays a central role in preconditioning the mixed layer and maximizes the turbulent mixing