factors controlling the cenozoic sequence development in the eastern parts of the north sea the causal relationship between the cenozoic sequence development in the southeastern north sea basin and sea level changes climatic fluctuations and tectonic events is unravelled by relating variations in the relative sea level and base level based on interpretations of seismic surveys to published 18 o variations and eustatic changes the latter curve is based on the earth9s orbital forcing and here informally termed as the gsi curve the analysis shows that the cenozoic sequence development in the southeastern north sea was influenced by climatically and tectonically induced sea level changes the major cenozoic sequence stratigraphic boundaries lower order are highly influenced by tectonic events e g uplift of fennoscandia and increased subsidence rates in the basin centre reactivation of mesozoic fault zones controlled the deposition of minor sand bodies transported to the centre of the basin during the late palaeocene by mass flows the location of an oligocene mound structure which constitutes part of a sequence is controlled by the overall palaeotopography of the basin and local fault related depressions correlation between i the ages of our sequences and the 18 o variations in the oligocene succession and ii the gsi curve and the base level fluctuations of the late miocene and younger sequences show that the generation of the higher order sequence boundaries were driven by glacio eustatic sea level changes a climatic control of the sequence formation due to glacio eustatic sea level changes is therefore suggested for the oligocene and pliocene sequences and probably also for the upper miocene sequences

isostasy of fracture zones in the atlantic ocean the cross spectral method of studying the isostasy was applied to profiles of gravity and topography which run across fracture zones in the atlantic ocean between 40 sup 0 n and 40 sup 0 s 30 section in total were used each section 400 km long in wavelengths 25 to 80 km the coherence of the free air gravity anomaly and topography attains 0 8 while the phase is close to zero which indicates that the disturbances in gravity are controlled by the topography and its isostatic compensation the experimental isostatic response function admittance deduced in this study is compared with previous results which relied on different spatial distribution of data a single mechanism of isostasy can explain well the gravity anomalies across fraction zones and across the median valley of the mid atlantic ridge a basic feature of this mechanism is the elastic lithosphere 6 to 9 km in thickness we show that the topography and gravity anomalies over the mid atlantic ridge crest are essentially three dimensional nevertheless the admittance is reliable computed from a set of profiles by using the method of d mckenzie and c bowin this possibility is provided by the favorable pattern of the topography spectrum in the area under consideration

on isostasy at atlantic type continental margins cross spectral techniques have been used to analyze the relationship between free air gravity anomalies and topography of approximately 100 profiles over the continental margins of eastern north america southwest africa and the coral sea lord howe rise the resulting admittance functions for these margins have been interpreted in terms of the flexure model of isostasy the relatively young coral sea lord howe rise margin is associated with the lowest value of the effective elastic thickness te 5 km while the relatively old eastern north american margin is associated with the highest value 10 te 20 km thus te appears to increase with the age of the margin these results which are consistent with flexure studies from the major ocean basins have been interpreted in terms of a simple model in which the flexural strength of the lithosphere increases with age the model suggests that a low rigidity plate or airy type model is most applicable early in rifting history while a high rigidity plate is more applicable later in margin evolution thus sediments at a margin initially load a relatively thin and hot plate while sediments later in margin evolution load a relatively thick and cold plate the model explains a number of features of the tectonic stratigraphic evolution of margins these include a change in flexural style from a narrow and deep basin to a broad and shallow basin coastal plain onlap and uplift in the continental interior furthermore the flexure model of isostasy contributes in a major way to observed free air gravity anomalies at continental margins in particular the model explains the existance of airy isostatic gravity anomalies at margins the amplitude and wavelength of these anomalies are a function of the sediment supply the type of mechanisms controlling sediment deposition up building and or out building and the thermal structure history and age of the margin

sequence stratigraphy of the upper oligocene lower miocene of eastern jylland denmark role of structural relief and variable sediment supply in controlling sequence development the upper oligocene lower miocene succession in eastern jylland can be subdivided into three sequences a c from older to younger deposited on and around the ringkobing fyn high the development of the sequences reflects a complex interaction between eustatic sea level changes physiography and variable sediment supply superimposed on this frequent storms promoted longshore sediment transport and the development of spit systems adjacent to structural highs as a consequence sequence boundaries and flooding surfaces are not always expressed as portrayed in conventional sequence models sequence boundaries or flooding surfaces may only be marked by subtle changes in depositional environment that can only be revealed by careful integration of sedimentological observations with palynological data the influence of the topography resulted in the development of brackish water basins that were sufficiently large to permit the deposition of hummocky cross stratified sands with muds these deposits are overlain by clean hummocky and swaley cross stratified sands that were deposited in a fully marine high energy environment this evolution from mud rich storm influenced sediments to sand dominated shoreface sediments resulted from a rise in sea level and was not the result of shoreface progradation and downstepping during a sea level fall in addition to the topographic control on sequence development sediment supply to the study area changed significantly during the deposition of the three sequences initially the basin was sediment starved favouring the formation of glaucony rich sediments the sediment input gradually increased and the influence of structural highs and lows became less significant with time consequently both sequence boundaries and flooding surfaces are characterized by more conventional features in the younger part of the succession where a basinward displacement of the shoreline resulted in thick lowstand delta deposits

isostasy of the northern bay of biscay continental margin summary spectral analysis of eight marine gravity profiles and seven seasat profiles combined with corresponding bathymetric data over the northern bay of biscay origin yield identical admittance functions for wavelengths greater than 120 km the resulting admittance function has been interpreted in terms of an airy model of compensation for wavelengths greater than 250 km and in terms of an elastic plate model of compensation for shorter wavelengths the airy model corresponds to a crustal thickness variation across the margin the plate model with an elastic thickness of 8 km is associated with the regional compensation of a sedimentary load which was probably emplaced during and just after rifting

thermal isostasy in the south atlantic ocean from geoid anomalies abstract transfer functions admittances were computed for the main tectonic units of the south atlantic ocean using the detailed seasat geoid ensemble averaging in the two dimensional wavenumber domain was applied the topography of the walvis ridge and rio grande rise visually correlates with the local geoid i e the difference between the total seasat geoid and first ten harmonics of the grim 3 model the mid atlantic geoid visually correlates with the total geoid sea gravimetry was used to evaluate the contribution of mechanical isostasy to the geoid admittances computed from the geoid and from gravimetry data agree well in the short waveband wavelengths shorter than 300 km a deviation at longer wavelengths is found between the observed admittance and the one due to mechanical isostasy for the southwestern walvis ridge it is explained with a density perturbation at about 20 km deep the admittance for the mid atlantic ridge is interpreted in terms of a boundary layer model and an average thickness of 30 km for the thermal lithosphere is obtained

an index for tropical temperate troughs over southern africa strong cases of the tropical temperate troughs ttt that are responsible for the most of the summer rainfall over subtropical southern africa are analyzed an index for identifying the ttt is introduced for the first time using anomalies of outgoing longwave radiation olr and the wind the ttt is associated with a ridge trough ridge wave like structure in the lower troposphere over southern africa and the adjoining indian ocean therefore the index considers physical processes that occur over southern africa adjoining the atlantic and indian oceans to depict the variability of the ttt events unusually strong ttt events are identified when the standard deviations of the ttt indices defined by the olr and wind anomalies in the selected regions are above 1 5 and 0 5 respectively after applying this criterion and filtering out consecutive events 55 ttt events are identified during the study period of december january february seasons from 1980 1981 to 2009 2010 from the composite analyses of those 55 events it is found that the ttts evolve with suppressed enhanced convection over the southwest indian ocean adjacent to madagascar southern africa the suppressed convection is in turn found to be associated with the enhanced convection around sumatra in the southeast tropical indian ocean this may explain why more ttt events occur in la nina years as compared to el nino years time evolution of the canonical ttt event shows that it starts 3 days prior to the mature phase of the event suggesting possible predictability after reaching a matured state the system moves east toward the indian ocean and decays within the subsequent couple of days in addition the intertropical convergence zone itcz structure changes over southern africa madagascar during the ttt event and remains similar to climatology over other regions the results indicate that the continental part of the itcz intensifies prior to the ttt event and then spreads southward following the mid latitude influence during and after the event

predicting the pinchout distance of shoreline tongues sand rich shoreline tongues are common features of the stratigraphic record and many of them are important petroleum reservoirs the basinward extent of such shallow marine deposits is highly variable from a few to a few hundred kilometres although indirect information exists the question as to what parameters actually cause this variation and their relative importance has not been addressed here it is argued that the sand pinchout distance of regressive to transgressive shoreline tongues is controlled by 1 the type of depositional system e g fluvial tide or wave dominated 2 the regressive and transgressive shoreline trajectories and 3 the depth of transgressive erosion in contrast to the shoreline trajectory the angle of turnaround defined by the pathway taken by the regressive and subsequent transgressive shorelines is simple to measure and gives a first approximation of the pinchout distance for otherwise equal systems the pinchout distance is inversely related to the angle of turnaround

seasat observations of lithospheric flexure seaward of trenches lithospheric flexure seaward of deep ocean trenches is evident in seasat altimeter observations of the marine geoid in fact mechanical models of lithospheric flexure can be tested directly on the seasat altimeter data we have used a simple elastic model for the oceanic lithosphere and after least squares adjustments have recovered estimates of model parameters including outer rise or amplitude or wavelength and effective lithospheric thickness effective lithospheric thicknesses have been recovered for six regions the mariana the kuril the philippine the aleutian the izu bonin and the middle america or s these results support the proposition that effective thickness te increases with age of lithosphere in approximate accord with the relation te c age1 2 where c 4 km m y 1 2 in fact our altimetric results agree more closely with this relation than do published results based on bathymetric data the close agreement with the thickness age relation suggests that there is no longer any need to assume that significant horizontal compression acts across the kuril marianas and izu bonin trenches this thickness age relation implies that flexural strength of the oceanic lithosphere is temperature controlled

relationships between cut off lows and the semiannual and southern oscillations the characteristics of southern cut off lows cols are studied for the period 1979 2008 the systematic identification of cols is realized by applying an original automated scheme using mean daily geopotential height and air temperature at 500 hpa ncep doe ii reanalysis data from closed lows trajectories established from the equator to the polar jet stream extratropical lows are analyzed and the stage of cut off is defined as a secluded low presenting a cold core from 4 843 cases the general col features are presented and confirm several previous results such as the geographic distribution which shows that they are more frequent in the latitudinal band contained between 20 s and 45 s and in close proximity to the continents on a seasonal time scale cols are more numerous from late summer to autumn with a maximum of frequency in march april in winter june july august they are fewer but deeper than during the rest of the year in the median domain 32 5 s the annual cycle of the frequency is bimodal and present two peaks during transitional seasons in this zone the seasonal cycle varies in accordance with the semiannual oscillation thereby when the meridional gradient of temperature pressure is reinforced between mid and high latitudes cols are more frequent in the median domain over the period 1979 2008 the annual cols frequency exhibits a positive trend of about 25 this increase is associated with a widening of the latitudinal domain of occurrence equatorward as well as poleward the trend is linked with an abrupt positive shift in the number of cols generation between 1998 and 1999 the geographical distribution of cols frequency varies significantly in accordance with el nino southern oscillation with more col s at lower higher latitudes during la nina el nino events principally in the southern pacific

the angola low relationship with southern african rainfall and enso the main states of the angola low al are identified using clustering analysis applied to daily anomalous patterns of 700 hpa wind vorticity over angola and adjacent countries from november to march for the 1980 81 2014 15 period at the daily timescale we examine the extent to which the main states of the al modulate daily rainfall over southern africa at the interannual timescale we assess both the relationship between the occurrence of these al states and el nino southern oscillation enso and the role of the al in explaining enso s failure in driving southern african rainfall at times three reanalyses are considered to account for uncertainties induced by the scarcity of data available for assimilation over southern africa three preferential states of the angola low are identified al state close to its seasonal climatology with slight zonal displacements anomalously weak al state and anomalously strong al state with meridional displacements these different states all significantly modulate daily southern african rainfall near climatological al state promotes wet rainfall anomalies over eastern subtropical southern africa and dry rainfall anomalies over its western part a slight westward shift in the near climatological position of the al leads to reversed zonal gradient in rainfall the remaining regimes significantly modulate the meridional gradient in southern african rainfall anomalously weak and anomalously northward al states promote wet rainfall anomalies over tropical southern africa and dry rainfall anomalies over subtropical southern africa the reverse prevails for anomalously southward al at the interannual timescale enso significantly modulates the seasonal occurrence of most al states in the three reanalyses anomalously weak and southward al states are more strongly correlated with regional rainfall than enso in all reanalyses suggesting that accounting for al variability may improve seasonal forecasts case study analysis of the major 1982 83 and 1997 98 el nino events suggests that the weak rainfall anomalies and strong seasonal al in 1997 98 may result from counteracting effects between enso and indian ocean coupled modes of variability

variations of elastic plate thickness at continental thrust belts after examining 15 reliable estimates of the elastic thickness of the lithosphere where it underthrusts mountain belts in europe asia and the americas we conclude that the strength of continental lithosphere as a function of depth must be very different from that of oceanic lithosphere depending on the state of stress continental lithosphere may be either very much stronger or very much weaker than would be predicted for oceanic lithosphere of the same thermal age we explain this observation as the result of two competing effects a thicker thermal plate beneath the continents which allows a deeper elastic ductile transition for plates more than 100 million years old and a low activation energy for ductile creep in the continental crust which leads to massive failure of the upper elastic lithosphere at high bending stresses the 100 km values for elastic plate thickness of billion year old lithosphere require a thermal plate thickness of at least 250 km the magnitude of apparent thinning of the elastic plate at high stress is consistent with that calculated from a simple yield envelope which includes a ductile zone in the lower crust the low yield strength of continental materials leads to correlations between effective elastic plate thickness and all of the following dip of the underthrust plate radius of curvature of the thrust front in map view and total length of the mountain belt using insight derived from laboratory experiments on the buckling of spherical shells and drawing analogies with the geophysical characteristics of oceanic subduction zones we arrive at the following sequence of causes and effects the primary variable is the dip of the downgoing plate presumably prescribed by its own excess mass and pressure exerted by dynamic flow in the mantle where this dip is steep the rigidity of the plate is weakened due to inelastic yielding the weakened plate can then buckle at small wavelengths into short arcuate mountain belts thus we believe that the mantle ultimately controls the pattern of surface tectonics but that the nonelastic rheology of the lithosphere is the mechanism by which that control is imposed

admittance signatures of rifted and transform margins examples from eastern canada examination of the gravity and bathymetry data across the rifted scotian margin and the sheared grand banks margin off the canadian east coast using a spectral analysis or admittance approach yielded different results the admittance for the scotian margin best fitted a regional compensation model in contrast a local compensation mechanism reproduced the transfer function for the grand banks margin the results for the longer wavelengths were verified using satellite altimetry data the effect of a hidden or subsurface load was investigated for both margins and this was also found to differ the differences in the compensation mechanism between rifted and sheared margins was attributed to their formation mechanisms

on the evolution of rifted continental margins comparison of models and observations for the nova scotian margin summary a model for the formation and evolution of rifted continental margins based on lithospheric extension during rifting and its thermal and mechanical consequences is proposed model predictions are then compared with geological and geophysical observations from a transect of the 185 ma old rifted margin off nova scotia through the scotian basin three kinematic models of the rifting process are discussed these are 1 the uniform extension model in which the amount of extension is uniform with depth but varies with position across the margin 2 the uniform extension and melt segregation model which has similar properties but also provides an explanation for the properties of the extended continental crust and its transition to oceanic crust by postulating that basaltic melt segregates from the asthenosphere and migrates to the crust and 3 the depth dependent extension model in which the first order consequences of rapidly changing rheological properties with depth in the lithosphere are included by decoupling the lithosphere into two zones with depth each of which undergoes differing amounts of extension these rift models predict the form of crustal and lithospheric thinning subsidence and temperature change once the amount of extension has been determined this is estimated from seismic measurements of present crustal thickness on the assumption that the crust had a uniform thickness equal to that currently measured in the adjacent continental region before rifting occurred rifting is also considered to occur instantaneously a time stepping thermo mechanical model is used to predict the cooling of rifted margin additional thermal contraction subsidence and its amplification by water and sediment loading thermal aspects are calculated using a finite difference model of time dependent conductive heat transport whereas regional isostatic response to loading is calculated by a finite element model the models are coupled because the temperature distribution is used to define a rheological lithosphere an elastic region with thickness that varies in time and space as the model evolves for flexural calculations in the mechanical model secondary coupling occurs through perturbations to the temperature field by sedimentary thermal blanketing and advection of heat during isostatic adjustment the model predictions of 1 sedimentary basin stratigraphy 2 moho position 3 free air gravity anomaly 4 age depth relations for deep exploratory wells and 5 subsidence and temperature histories agree well with observations from the scotian basin additional effects due to sedimentary and crustal radiogenic heat production lateral heat transport and the possible existence of a near surface brittle listric faulted region created during rifting are also considered it is concluded that a model in which rifting occurred by depth dependent extension and which includes a finite thickness for the rheological lithosphere radiogenic heat production in the sediments and crust and a brittle listric faulted crustal layer affords an accurate description of the first order processes that occur during rifting and evolution of this margin

crustal structure and the mechanical properties of extended continental lithosphere in the valencia trough western mediterranean seismic refraction and reflection gravity and well data have been used to constrain the structure and evolution of the valencia trough a young extensional basin in the western mediterranean seismic refraction data reveal the present day crustal structure while backstripping of seismic reflection and well data reveal the structure at the time of rifting by comparing the seismically constrained crustal structure to that inferred from backstripping we have been able to evaluate whether the moho is in the expected position given the tectonic subsidence uplift and sediment loading history of the trough the best overall fit between the predicted and seismically constrained crustal structure in the trough is for a model in which the extended continental crust and lithosphere has acquired little or no strength following rifting a low strength is in accord with the observed free air gravity anomaly as well as results from other types of rift basins such as the north sea and the continental margin off the east coast of the usa there are discrepancies between the observed and predicted moho depths beneath the flanks of the valencia trough but they are attributed to either the removal of crustal material during or following rifting iberian peninsula or to orogenic loading of previously extended continental crust mallorca the largest discrepancy up to 10 km correlates with the ebro delta which has prograded into the trough by more than 60 km since the pliocene the discrepancy cannot be explained by the same large scale processes that modified the moho beneath the trough flanks and requires that the lithosphere beneath the ebro delta region is associated with a high 60 t c

water vapour transport from the tropical atlantic and summer rainfall in tropical southern africa an empirical orthogonal functions analysis of the onshore flow of moisture along the west coast of southern africa using ncep doe amip ii re analyses suggests two dominant modes of variability that are linked to a variations in the circulation linked with the south atlantic anticyclone b the intensity of the flow that penetrates from the tropical atlantic the second mode referred as the equatorial westerly mode contributes the most to moisture input from the atlantic onto the subcontinent at tropical latitudes substantial correlations in austral summer between the atlantic moisture flux in the tropics and rainfall over the upper lands surrounding the congo basin suggest the potential role played by this zonal mode of water vapour transport composites for austral summer months when this equatorial westerly mode had a particularly strong expression show an enhanced moisture input at tropical latitudes that feeds into the deep convection occurring over the congo basin sustained meridional energy fluxes result in above normal rainfall east and south of the congo belt during years of reduced equatorial westerly moisture flux a deficit of available humidity occurs in the southern tropics a concomitant eastward shift of deep convection to the southwest indian ocean and southeastern africa leads to below normal rainfall over the uplands surrounding the congo basin

lithospheric structure of a nascent spreading ridge inferred from gravity data the western gulf of aden the aden spreading ridge somalia arabia plate boundary does not connect directly to the red sea spreading ridge it propagates toward the east african rift through the afar depression where the presence of a hot spot has been postulated from seismological and geochemical evidence the spreading direction n37 e is highly oblique to the overall trend n90 e of the ridge we present and interpret new geophysical data gathered during the tadjouraden cruise r v l atalante 1995 in the gulf of aden west of 46 e these data allow us to study the propagation of the ridge toward the afar and to discuss the processes of the seafloor spreading initiation we determine the lithospheric structure of the ridge using gravity data gathered during the cruise with the constraint of available refraction data a striking bouguer anomaly gradient together with the identification of magnetic anomalies defines the geographical extent of oceanic crust the inversion of the bouguer anomaly is performed in terms of variations of crustal thickness only and then discussed with respect to the expected thermal structure of the mantle lithosphere which should depend not only on the seafloor spreading but also on the hot spot beneath east africa our results allow us to define three distinct lithospheric domains in the western gulf of aden east of 44 45 e the lithosphere displays an oceanic character thermal subsidence recorded for the last 10 ma and constant crustal thickness between 43 30 e and 44 10 e the lithosphere is of continental type but locally thinned beneath the axial valley the central domain defined between 44 10 e and 44 45 e is characterized by a transitional lithosphere which can be seen as a stretched continental crust where thick blocks are mixed with thinned crust it displays en echelon basins that are better interpreted as extension cells rather than accretion cells

a southern hemisphere wave response to enso with implications for southern africa precipitation ensemble gcm simulations with an imposed idealized warming of the eastern pacific ocean reveal two wave anomalies in the southern hemisphere one in the eastern and one in the western hemisphere both are statistically significant at the 99 confidence level application of a steady state linear model and a rossby wave source analysis is used to diagnose the causes of the waves the western hemisphere wave is forced by the advection and stretching of planetary vorticity by the divergent flow from the southern hemisphere component of the central pacific twin anticyclones that straddle the equator during warm events the eastern hemisphere wave is a result of the northeastward shift of the south indian convergence zone sicz that in turn is forced from the upper troposphere by convergence to the north an upper level convergence maximum over the equatorial indian ocean induces divergence to the south encouraging vertical motion and precipitation to the northeast of the sicz s normal position the resulting anomalous upper level convergence in the climatological position of the sicz as well as the anomalous vorticity flux convergence by the transients associated with an equatorward shift of the storm track behind the sicz force the eastern hemisphere rossby wave since a shift of the sicz is a fairly robust observed consequence of enso events these results suggest the mechanism by which drought conditions develop over southern africa at the height of many warm events seasonal prediction capabilities in this region can be improved by monitoring and understanding the details and consequences of the adjustment of the walker circulation near the equator outside of the pacific ocean basin

crustal structure of the celtic sea and western approaches from gravity data and deep seismic profiles constraints on the formation of continental basins a free air anomaly map of the celtic sea and the western approaches is presented including all available marine gravimetric data and bouguer anomalies on land n60 features are predominant in the area they correspond to the n60 so called caledonian grain which played a major role in the variscan orogeny and in the formation of the permo triassic sedimentary basins the fundamental new point which comes out from this gravimetric map is the existence of a closely spaced pattern of n105 features which we regard as late carboniferous transpressional structures in the eastern pan of the celtic sea thrusts are in the same n105 direction west of 6 w longitude however folds and thrusts trend preferentially in a n60 direction following the older grain there the n105 lineaments may be regarded as dextral shear structures with a possible compressive component the hercynian shortening of the celtic sea domain located between the variscan front and the lizard suture resulted from the displacement along the n160 direction of the two adjacent rigid domains north of the variscan front the n105 and n135 features were possibly active in more recent times then both the n60 and n105 trends controlled the formation of permo triassic basins the n105 directions being transfer faults two dimensional gravity modelling of the swat profiles in the celtic sea shows that the base of the reflective lower crust may be associated with the moho discontinuity everywhere in the celtic sea except below the saint george s channel basin the lower crust does not change significantly in depth and thickness beneath the permo triassic basins none of the available models simply satisfies such conditions they all require at least a modification of the geometry of the lower crust after the formation of the celtic sea basins nevertheless if the simple shear model can be ruled out mainly from structural arguments the uniform stretching and to a lesser degree the thermomechanical models seem to be more relevant models however two additional conditions are necessary 1 the preservation of crustal seismic features formed before the creation of basins must be explained and 2 a significant portion of the volume of the stretched lower crust about 40 of this volume for the north celtic sea basin must be added below or perhaps partly above the lower crust by lateral flow of the crust or at the expense of the upper mantle

circulation anomalies associated with tropical temperate troughs in southern africa and the south west indian ocean daily rainfall variability over southern africa sa and the southwest indian ocean swio during the austral summer months has recently been described objectively for the first time using newly derived satellite products the principle mode of variability in all months is a dipole structure with bands of rainfall orientated northwest to southeast across the region these represent the location of cloud bands associated with tropical temperate troughs ttt this study objectively identifies major ttt events during november to february and on the basis of composites off ncep reanalysis data describes the associated atmospheric structure the two phases of the rainfall dipole are associated with markedly contrasting circulation patterns there are also pronounced intra seasonal variations in early summer the position of the temperate trough and ttt cloud band alternates between the swio and southwest atlantic in late summer the major ttt axis lies preferentially over the swio associated with an eastward displacement in the indian ocean high in all months positive events in which the ttt cloud band lies primarily over the swio are associated with large scale moisture flux anomalies in which convergent fluxes form a pronounced poleward flux along the cloud band this suggests that ttt events are a major mechanism of poleward transfer of energy and momentum moisture transport occurs along three principle paths 1 the northern or central indian ocean where anomalous fluxes extend eastward to the maritime continent 2 south equatorial africa and the equatorial atlantic 3 from the south within a cyclonic flow around the tropical temperate trough the relative importance of 2 is greatest in late summer thus synoptic scale ttt events over sa swio often result from large scale planetary circulation patterns hovmoeller plots show that ttt development coincides with enhanced tropical convection between 10 30 e itself exhibiting periodicity of around 5 days and often with convergence of eastward and westward propagating convection around 40 e harmonic analysis of 200 hpa geopotential anomalies show that ttt features are forced by a specific zonally asymmetric wave pattern with wave 5 dominant or significant in all months except february when quasi stationary waves 1 2 and 3 dominate these findings illustrate the importance of tropical and extratropical dynamics in understanding ttt events finally it is suggested that in november januar ttt rainfall over sa swio may be in phase with similar rainfall dipole structures observed in the south pacific and south atlantic convergence zones

crustal structure of the continent ocean transition off the cote d ivoire ghana transform margin implications for thermal exchanges across the palaeotransform boundary summary crustal structure of the continent ocean transition off the cote d ivoire ghana transform margin is determined by 2 d modelling of wide angle seismic data and gravity data the resulting models together with geological data recently collected by drilling on the margin are compared with available thermomechanical models of transform margins in particular we test the predicted effects on the transform margin crust of continental heating by the adjacent oceanic lithosphere these effects include i ductile flow of the lower continental crust either parallel to the transform direction or perpendicular to it from the continent towards the ocean and ii thermal uplift of the transform margin in the region of the cote d ivoire ghana transform margin the seismic and gravity data indicate that the continental crust remains uniform in thickness as the continent ocean boundary is approached the interpreted models lack a transitional domain between continental and oceanic crusts and abnormally thin oceanic crust is found along the margin these results exclude large scale ductile flow of lower continental crust during the margin formation the geological data are moreover not consistent with thermal uplift of the margin during the period of contact between the transform margin and the spreading centre our geophysical and geological data thus infer only moderate heating of the transform continental margin by the adjacent oceanic lithosphere moderate heating of the cote d ivoire ghana transform margin during margin formation implies that the thermal exchange between the transform margin and the adjacent spreading centre were lower than predicted by available thermal models two main factors may have contributed to reduce thermal exchanges across the continent ocean boundary the first factor is that the oceanic edge may have been colder than assumed by thermal models an abnormally cold spreading axis along the transform margin when the oceanic crust was emplaced is supported by the atypical structure of the oceanic crust along the cote d ivoire ghana transform margin the oceanic crustal structure is similar to that found along oceanic fracture zones where oceanic crust is also emplaced near a ridge transform intersection in both cases abnormally low thermal gradients at the spreading centre along the transform margin may be explained by the cumulative effect of i a cold edge effect of the adjacent continental lithosphere ii accretion at the end of a ridge segment away from the main magma supply point along the spreading axis and iii an efficient upward cooling of the oceanic lithosphere owing to deep hydrothermal circulation within the faulted lithosphere the second factor causing moderate thermal exchanges is the possibility of large amounts of water in oceanic lithospheric faults which reduces the lateral thermal conduction in the lithosphere since water is much less conductive than rock during the margin formation the oceanic edge thus seems to have acted as a thermal buffer between the cold continental margin and the hot spreading centre we propose that this thermal buffer hypothesis may be generalized to most transform margins implying a lower amount of continental heating than assumed by the available thermomechanical models

deep seismic reflection and refraction profiling along the aquitaine shelf bay of biscay summary the 300 km ecors bay of biscay profile was carried out along the aquitaine shelf and comprised a complete set of experiments including zero offset and 7 5 km constant offset vertical seismic reflection and six expanding spread profiles large offset recordings were fundamental for the definition of the layered lower crust and the moho while esps provided decisive complementary information for the geological interpretation these data show a strong variation in crustal thickness from about 20 km beneath the rifted parentis basin a failed arm of the oceanic bay of biscay up to 35 km to the north below the armorican shelf in the hercynian domain and to the south below the cantabria shelf in the vicinity of the pyrenean deformation front the results have important implications for the behaviour of the crust during the formation of rifted sedimentary basins and during continental collision

millennial scale depositional cycles from the holocene of the po plain italy the holocene depositional history of southeastern po plain on time scales of 103 yr is reconstructed based upon integrated sedimentological and micropalaeontological analyses of nine continuously cored boreholes about 40 m deep major palaeoenvironmental changes include the rapid landward migration of a barrier estuary lagoon system during the early middle holocene transgressive systems tract tst followed by extensive delta progradation in the last 6000 yr highstand systems tract hst detailed facies analysis of cores combined with the identification of 12 microfossils benthic foraminifer and ostracod associations allow an ultra high resolution sequence stratigraphic framework to be reconstructed particularly eight small scale high frequency cycles about 3 5 m thick and spanning intervals of time of about 1000 yr can be physically traced throughout the study area interpretation of these cycles which are invariably bounded by sharp flooding surfaces and generally show internal shallowing upward trends parasequences indicates that relative sea level changes during the holocene were episodic and punctuated by rapid phases of sea level rise followed by periods of stillstand or decreasing sea level rise from seaward to landward locations parasequence boundaries document beach barrier migration bay head delta abandonment and increasing accommodation in the coastal plain the ensuing phases of sea level stillstands resulted in the progressive filling of the newly formed accommodation space through beach progradation extensive mud deposition in behind barrier lagoonal estuarine and marsh deposits and aggradation in bay head delta systems at the head of estuaries eustacy appears to be the major controlling factor of the retrogradational stacking pattern of parasequences within the tst by contrast a complex interplay of eustacy sediment supply and subsidence with an increasing influence of autocyclic mechanisms such as channel avulsion and delta lobe abandonment controlled facies architecture within the hst the maximum flooding surface cannot be assumed to be synchronous its timing being strongly dependent upon local variations in sediment influx and subsidence this study shows that the micropalaeontologic characterization of mud prone coastal plain and estuarine successions in terms of water depth and salinity can lead to very accurate sequence stratigraphic interpretations allowing identification of parasequence boundaries that may not be detected by conventional stratigraphic approach

a decadal prediction case study late twentieth century north atlantic ocean heat content an ensemble of initialized decadal prediction dp experiments using the community climate system model version 4 ccsm4 shows considerable skill at forecasting changes in north atlantic upper ocean heat content and surface temperature up to a decade in advance coupled model ensembles were integrated forward from each of 10 different start dates spanning from 1961 to 2006 with ocean and sea ice initial conditions obtained from a forced historical experiment a coordinated ocean ice reference experiment with interannual forcing core ia which exhibits good correspondence with late twentieth century ocean observations from the north atlantic subpolar gyre spg region north atlantic heat content anomalies from the dp ensemble correlate highly with those from the core ia simulation after correcting for a drift bias in particular theobservedlarge rapid rise in spgheatcontentin themid 1990sis successfullypredicted in the ensemble initialized in january of 1991 a budget of spg heat content from the core ia experiment sheds light on the origins of the 1990s regime shift and it demonstrates the extent to which low frequency changes in ocean heat advection related to the atlantic meridional overturning circulation dominate temperature tendencies in this region similar budgets from the dp ensembles reveal varying degrees of predictive skill in the individual heat budget terms with large advective heat flux anomalies from the south exhibiting the highest correlation with core ia the skill of the dp in this region is thus tied to correct initialization of ocean circulation anomalies while external forcing is found to contribute negligibly and for incorrect reasons to predictive skill in this region over this time period

a seismic refraction and reflexion study of the continent ocean transition beneath the north biscay margin the structure of the northern margin of the bay of biscay consists of a series of tilted and rotated blocks bounded by prominent listric faults whose polarity is consistently down toward the continent ocean boundary these blocks formed by rifting in late jurassic early cretaceous time and are now thinly covered by post rift sediments of aptian to recent age seismic refraction profiles were occupied on the shelf on either side of and across the continent ocean transition to the shelf using p ubs and o bs with explosives and a 4 x 1000 in 3 4 x 16400 cm 3 airgun array two ship expanding spread multichannel 48 trace seismic reflexion profiles and 30 km fixed offset reflexion profiles were located along the seismic refraction profiles on either side of the transition a two ship 30 km fixed offset multichannel profile was located across the transition as well as a 5 km fixed offset multichannel profile extending from the ocean crust to the shelf conventional 48 trace single ship multichannel profiles were located along all the refraction and two ship reflexion lines interpretation of the refraction profiles has been made by using ray tracing as well as synthetic seismograms conventional seismic processing techniques have been used to prepare the two ship multichannel seismic data for interpretation the survey is believed to be the first attempt to apply two ship multichannel seismic data to the study of the change in crustal structure of a rifted passive margin from the shelf to the ocean crust the results from the experiment led to the identification of a zone of transition between continental and oceanic crust about 8 km wide the seismic refraction data show progressive thinning of the continental crust from 33 km to about 5 km close to the transition zone however extension values calculated in the upper crust from the rotation of fault blocks are much less 1 1 1 4 and suggest that the majority of the thinning is achieved by extensive attenuation of the lower crust

modification of the southern african rainfall variability enso relationship since the late 1960s analysis of 149 raingauge series 1946 1988 shows a weak positive correlation between late summer rainfalls january march in tropical southern africa and the southern oscillation index soi the correlation coefficients have been unstable since world war ii they were close to zero before 1970 and significant thereafter before 1970 southern african late summer rainfalls were more specifically correlated with regional patterns of sea surface temperature sst mainly over the southwestern indian ocean after 1970 teleconnections with near global sst anomaly patterns i e over the central pacific and indian oceans dominate the regional connections the increase in the sensitivity of the southern african rainfall to the global so related circulation anomalies is simultaneous with the correlation between soi and more extensive sst anomalies particularly over the southern indian ocean this feature is part of longer term decadal global sst variability as inferred from statistical analyses numerical experiments using the meteo france general circulation model arpege climat are performed to test the impact of the observed sst warming in the southern indian and extratropical oceans during el nino southern oscillation enso events on southern african rainfall simulated results show that enso events which occurred in the relatively cold background of the pre 1970 period in the southern oceans had a little effect on southern africa climatic conditions and atmospheric circulation by contrast more recent enso events with warmer sst over the southern oceans lead to a climatic bipolar pattern between continental southern african and the western indian ocean which is characterized by reduced enhanced deep convection and rainfall over the subcontinent the western indian ocean a weaker subtropical high pressure belt in the southwestern indian ocean is also simulated along with a reduced penetration of the moist southern indian ocean trade winds over the southern african plateau these results are consistent with the strong droughts observed over all southern africa during enso events since 1970

thermal isostasy response of a moving lithosphere to a distributed heat source spreading ridges and hot spot swells are identified by their high surface heat flow shallow seafloor and high geopotential to understand these and other thermotectonic features the oceanic lithosphere is modeled as a thermomechanical boundary layer moving through a three dimensional time independent heat source the heat source mimics the heat advection associated with a spreading ridge or hot spot without introducing the nonlinearities of these flow processes the fourier transforms of three green s functions response functions which relate the three observable fields to their common heat source are determined analytically each of these reponse functions is highly anisotropic because the lithosphere is moving with respect to the source however the ratio of the gravity response function to the topography response function i e gravity topography transfer function is nearly isotropic and has a maximum lying between the flexural wavelength and 2 times the thickness of the thermal boundary layer the response functions are most useful for determining the surface heat flow seafloor topography and geopotential for complex lithospheric thermal structures in practice these three observables are calculated by multiplying the fourier transform of the heat source by the appropriate response function and inverse transforming the products almost any time independent thermotectonic feature can be modeled using this technique included in this report are examples of spreading ridges and thermal swells although more complex geometries such as ridges offset by transform faults and rrr type triple junctions can also be modeled because forward modeling is both linear and computationally simple the inverse of this technique could be used to infer some basic characteristics of the heat source directly from the observed fields

moisture transport between the south atlantic ocean and southern africa relationships with summer rainfall and associated dynamics moisture exchange between the south atlantic and southern africa is examined in this study through zonal moisture transport along the west coast of southern africa a multivariate analysis of the zonal flow of moisture computed from ncep doe amip ii re analyses reveals a primary mode of variability typical of variations in intensity and of the latitudinal migration of the circulation associated with the midlatitude westerlies and the south atlantic anticyclone in austral summer january february this mode referred to as the south atlantic midlatitude mode is found to be well correlated with rainfall over southern africa i e to the south of the upper lands surrounding the congo basin its positive negative phases are found to correspond with surface pressures changes over the south atlantic region in austral summer when the south atlantic anticyclone is shifted northward southward respectively such changes are accompanied by dipole like sst anomalies in the midlatitude south atlantic ocean while simultaneous sst anomalies with a similar structure are also found over south indian ocean regions in january february positive negative events linked to the south atlantic midlatitude mode are marked by meridional shifts northward southward and weakening strengthening of the itcz over the southern tropics together with modulations in intensity weakened sustained of the angola low which could act as a tropical source of moisture for tropical temperate troughs ttts in association with a strengthened weakened zonal component of the southern extension of the african easterly jet aej this could modulate the meridional transfer of moisture south of 15 s to the advantage detriment of angolan coastal regions where above below rainfall are expected variations in the latitudinal position northward southward of the south atlantic anticyclone and thus of the midlatitude westerlies are also found to reduce favour moisture advection towards southern africa subtropics allowing the southern indian trades to penetrate less more over the subcontinent south of 25 s this would create a situation where convection processes are inhibited supported within the sicz ttts region resulting in drier wetter conditions locally for positive negative events respectively

on the interpretation of frequency response functions for oceanic gravity and bathymetry summary oceanic bathymetry and gravity comprise a geophysical system which is often characterized by a linear frequency response function or admittance the actual behaviour of this system differs in important respects however from that of an ideal linear model three sources of such differences are considered in this study the presence of noise in the data non linearity due to finite amplitude and intrinsic two dimensionality of the data fields the high positive correlation between admittance amplitude and coherence estimates obtained in a number of studies indicates that the noise is not normally distributed with zero mean as generally assumed non linear modification of the admittance results from the finite amplitude of the bathymetry and the non linear elasticity of the lithosphere the former effect increases with bathymetric roughness and is most pronounced for shortwavelength uncompensated bathymetry the latter is significant only if the deflection of the lithosphere is comparable to its elastic thickness as for certain large seamounts in the pacific ocean which were emplaced on lithosphere near ridge crests the most severe problem arises for features which are markedly two dimensional features typical of observed oceanic seamounts are characterized by admittances along tracks which differ substantially from those appropriate to one dimensional bathymetry this difference occurs primarily in the long wavelength portion of the admittance rendering problematic the comparison of observed admittances or gravity anomalies with theoretical expressions

the impact of enso on southern african rainfall in cmip5 ocean atmosphere coupled climate models we study the ability of 24 ocean atmosphere global coupled models from the coupled model intercomparison project 5 cmip5 to reproduce the teleconnections between el nino southern oscillation enso and southern african rainfall in austral summer using historical forced simulations with a focus on the atmospheric dynamic associated with el nino overestimations of summer rainfall occur over southern africa in all cmip5 models abnormal westward extensions of enso patterns are a common feature of all cmip5 models while the warming of the indian ocean that happens during el nino is not correctly reproduced this could impact the teleconnection between enso and southern african rainfall which is represented with mixed success in cmip5 models large scale anomalies of suppressed deep convection over the tropical maritime continent and enhanced convection from the central to eastern pacific are correctly simulated however regional biases occur above africa and the indian ocean particularly in the position of the deep convection anomalies associated with el nino which can lead to the wrong sign in rainfall anomalies in the northwest part of south africa from the near surface to mid troposphere cmip5 models underestimate the observed anomalous pattern of pressure occurring over southern africa that leads to dry conditions during el nino years

washover fan and brackish bay sedimentation in the berriasian valanginian of bornholm denmark abstract the robbedale and jydegard formations berriasian valanginian of the danish island of bornholm represent a 100 m thick vertical sequence from shoreface foreshore and beach sands of a high energy coast through backbarrier flat bay margin pond and distal washover fan sand and clay brackish bay clay to fluvial sands the longevity of the backbarrier bay system c 10 myr thickness 100 m of the bay deposits and apparently stacked nature of the facies belts suggest a relatively stationary position of the individual subenvironments with only minor progradation this reflects strong tectonic control of the depositional system during an important phase of synsedimentary block faulting and wrenching along the tornquist zone the importance of washover fan sands in the backbarrier deposits and the lack of tidal indications in the whole sequence suggest a microtidal regime a system of migrating mud banks formed in shallow water on the landward side of the barrier the bay waters varied from almost fresh to brackish and anoxic conditions commonly occurred at the bottom adverse living conditions for most organisms in the bay caused seasonal possibly toxic dinoflagellate blooms resulting in mass mortality of infaunal bivalves bay margin ponds underwent periodic desiccation leading to mass mortality of freshwater gastropods as a general scenario it is envisaged that longshore currents redistributed bedload from a major delta and formed an extensive nw se barrier spit which partly enclosed a major bay to the ne the barrier was breached during heavy storms and the sand transported along the resulting washover channels was deposited on the backbarrier flat made up of the subaerial parts of coalescent washover fans enormous amounts of suspension load from the delta travelled further along the barrier to be deposited in the lee side bay

structural sedimentologic and sea level controls on sand distribution in a steep clinoform asymmetric wave influenced delta miocene billund sand eastern danish north sea and jylland abstract the lower miocene billund sand of jylland denmark provides an excellent opportunity to study the distribution of sands and the types of clinoform generated by a wave dominated delta prograding into a deep shelf environment in particular seismic sections the sand rich parts correlate with parallel clinoformal seismic facies in which the clinoforms dip 7 to 10 the stacking pattern of this seismic facies also indicates whether the progradation occurred during rising or falling sea level by displaying an ascending or descending shoreline trajectory respectively the billund delta was deposited in the eastern north sea basin during the early miocene and is on the available data recognized as a nw to se trending feature it forms a wave dominated delta with thick sand bodies deposited in relatively deep waters 100 m at the river mouth and in the up drift area of newly formed delta lobes sands and muds associated with a spit complex or a lagoonal complex dominated the down drift area in the distal delta front area alternating sands and muds were laid down the sands associated mainly with storm events progradation of the studied part of the delta occurred during high sea level and a subsequent fall in sea level that was caused by a eustatic fall during the mid aquitanian early miocene although sand intervals 10 to 20 m thick are common throughout the delta complex the thickest up to 100 m and cleanest sand is found in units deposited in narrow bands within structural lows and during periods of forced regression the billund delta may be an excellent analogue for hydrocarbon bearing wave dominated deltas and seems to exhibit similarities to jurassic deposits in the north sea area

a new analysis of gravity and topography data over the mid atlantic ridge non compensation of the axial valley abstract topographic and associated gravity signals often result from the interference of several phenomena in the present paper an admittance function for the superposition of several physical mechanisms acting in the same waveband is derived if the processes are not phase related the resulting admittance function is the average of the individual admittance functions weighted by the squared amplitude of the topography for each process we use this concept of superposition of different processes to understand the compensation of the atlantic ridge valley classical transfer function studies applied to slow spreading ridges have concluded that the topography was emplaced on an elastic plate about 10 km thick these analyses of gravity and topography seem to contradict the physical models explaining the median rift valley which is thought to be due to dynamical effects and thus to be uncompensated we obtain an average axial valley gravity and topography profile by stacking several profiles perpendicular to the mid atlantic ridge and subtracting a long wavelength thermal effect we find that the gravity over topography spectral ratio of the average axial valley signal is consistent with an uncompensated process our study thus confirms that the mode of formation of the axial valley of a slow spreading ridge involves an uncompensated mechanism the presence of an additional process characterized by low admittance values uncorrelated from one profile to the other is also suggested in order to explain the observed admittance function the study of the long wavelength 300 km gravity and topography signal leads us to invoke the cooling of the upper portion of the crust by water circulation and to exclude the presence of a large amount of partial melt at depth more than 5 over a 20 km thick layer at a mean depth of 60 km

the south indian convergence zone and interannual rainfall variability over southern africa abstract the south indian convergence zone sicz is identified in this paper as a region of enhanced precipitation extending off the southeast coast of southern africa during austral summer unlike the south pacific convergence zone the sicz is a land based convergence zone lbcz with position and intensity at least partially determined by surface conditions over southern africa an idealized gcm simulation is used to explore the basic dynamics of lbczs in the tropics and subtropics output from a realistic gcm simulation and the national centers for environmental prediction national center for atmospheric research 40 year reanalysis are analyzed to apply this basic dynamical framework to the case of the sicz in contrast to the intertropical convergence zone where column moisture convergence is primarily due to meridional wind convergence in the moist environment precipitation within the sicz and the lbczs in general is also supported by zonal wind convergence moisture convergence by transient eddy

a stability analysis of tropical ocean atmosphere interactions bridging measurements and theory for el nino abstract interactions between the tropical oceans and atmosphere permit a spectrum of natural modes of oscillation whose properties period intensity spatial structure and direction of propagation depend on the background climatic state i e the mean state this mean state can be described by parameters that include the following the time averaged intensity of the pacific trade winds the mean depth h of the thermocline and the temperature difference across the thermocline t a stability analysis by means of a simple coupled ocean atmosphere model indicates two distinct families of unstable modes one has long periods of several years involves sea surface temperature variations determined by vertical movements of the thermocline that are part of the adjustment of the ocean basin to the fluctuating winds requires a relatively deep thermocline and corresponds to the delayed oscillator the other family requires a shallow thermocline has short periods of a year or two has sea surface tempe

the horn graben and its relationship to the oslo graben and the danish basin abstract the tectonic development of the horn graben the danish basin and the oslo graben are compared with special emphasis on the timing of their initiation the comparison is based on seismic interpretation and is supported by analysis of tectonic subsidence devonian and carboniferous sedimentary strata and rotliegende volcanics constitutes the pre rift succession in the horn graben in the central part of the graben it rests unconformably on precambrian possibly dalslandian basement to the south on caledonian metamorphic basement whereas lower palaeozoics occur to the north the distribution of these pre devonian assemblages suggests initial early devonian uplift of the ringkobing fyn high as the lower palaeozoic sediments are believed to have covered the high originally further uplift appears to have taken place in the early permian a subdivision of the horn graben into a northern and a southern segment are recognized the rifting was apparently heralded only in the southern segment in the rotliegende and the main rifting phase did not start before the triassic subsidence modelling shows that the thermal anomaly created by rifting of the horn graben was less significant than in the danish basin and resulted in much less post rift thermal subsidence the reduced thermal anomaly may account for an earlier consolidation of the crust thereby rendering the area resistant to late cretaceous early tertiary inversion tectonism the oslo graben was tectonically active during late carboniferous to early permian times and essentially became inactive during triassic times when the main tectonism of the horn graben occurred subsidence modelling shows that the danish basin south of the fjerritslev trough was tectonically active mainly during the zechstein whereas the rapid triassic subsidence is modelled to be caused by phase transformations as indicated by the minor amount of basement attached faulting based on the differing subsidence patterns it is concluded that the three basins did not develop simultaneously and that they are not genetically related

origin and tectonic evolution of the caroline ridge and the sorol trough western tropical pacific from admittance and a tectonic modeling analysis abstract an independent caroline sea plate surrounded by prominent seismotectonic features is said to exist in the western tropical pacific the caroline sea plate is a transient feature existing only when the caroline philippine sea plate boundary is jumping to the caroline pacific boundary the origin and the tectonic evolution of the caroline ridge sorol trough region which forms the northern part of the caroline pacific plate boundary are examined using a standard admittance analysis a tectonic modeling study and additional direct gravity and magnetic analyses the observed admittance function is fitted well by shallow airy model in the 250 125 km 0 025 k 1 wavelength region whose average crustal thickness t c is 20 km and also by thin plate flexure model of isostasy within the diagnostic waveband of 250 80 km 0 025 k 1 with an effective elastic thickness t e of 5 7 km a simple interpretation of the observed admittance function is that the local airy model of isostasy is the main support mechanism in the study region for the longer wavelength more fundamental topography corresponding to that of the caroline ridge the caroline ridge is inferred to have formed in a near ridge tectonic setting on top of oceanic lithosphere which was young thin and weak at the time of emplacement the tectonic model study after an explanation for rifting along the mendana fracture zone in the nazca plate suggests that the sorol trough formed in the 17 7 ma interval splitting the caroline ridge into two longitudinal halves the rifting along the sorol trough which took place in the manner described in weissel and karner 1989 flexural uplift of rift flanks due to mechanical unloading of the lithosphere during extension j geophys res 94 13 919 13 950 necking of unbroken lithosphere post dated the formation of the caroline ridge by 10 15 m y during which time t e in the region increased to 5 10 km the rifting necking along the sorol trough represents a second loading event in the region the combined gravity effects of the rifting as well as the increase in the t e in the region from essentially nil to 5 10 km is reflected in the agreement between the observed admittance and the regional model with a 5 7 km t e in the wavelength region 80 km these results are consistent with the findings and the suggestions of the previous investigators in the region in that 1 the caroline ridge was constructed in the late oligocene by hot spot volcanism on top of oligocene seafloor of the caroline sea back arc basin 2 the eauripik rise genetically related to the caroline ridge formed on young and weak caroline basin lithosphere and is supported by airy manner crustal thickening and that 3 the lithosphere of the caroline ridge was young at the time of rifting necking along the sorol trough on the basis of the current results and the findings of the previous workers a tentative hypothetical rheological model for the crustal density structure of the caroline ridge sorol trough is also given the caroline sea plate appears to be bounded in the north and south by e w trending boundaries that deform diffusely while more normal narrow n s trending boundaries exhibiting more localized albeit slow deformation bound the plate in the east and west

remote effects of el nino and modoki events on the austral summer precipitation of southern africa abstractremote effects modulating the austral summer precipitation over southern africa during el nino el nino modoki events are investigated by analyzing the observed events during december february of the years from 1982 83 to 2010 11 based on the composite analyses it is found that southern africa experiences significantly below normal precipitation during el nino events compared to el nino modoki events during these latter events precipitation anomalies are not so significant although southern africa as a whole receives below normal precipitations the differences in the spatial distribution of precipitation over southern africa are seen to be related to the sea surface temperature sst anomalies of the equatorial pacific through atmospheric teleconnections the low level 850 hpa matsuno gill response to anomalously high precipitation over the pacific during el nino events results in an anomalous anticyclone extending from the equatorial to the subtropical south indian ocean these anomalous ant

interactions between synoptic intraseasonal and interannual convective variability over southern africa after removing the annual cycle a principal component analysis is applied to the daily outgoing longwave radiation anomaly field used here as a proxy for atmospheric convection the analysis is carried out over the southern african region 7 5 e 70 e 10 s 40 s for austral summer november through february for the period 1979 1980 to 2006 2007 the first five principal components pc are retained the first two pcs describe spatial patterns oriented north west to south east from tropical southern africa sa to the mid latitudes they are interpreted to be different possible locations for synoptic scale tropical temperate troughs ttt one dominant rainfall producing synoptic system in the region the phase relationship between these two pcs describes a tendency for these ttt to propagate eastwards from sa to the mozambique channel and southern madagascar the next three pcs describe convective fluctuations respectively located over the north west the south and the centre of sa their time series are significantly associated with madden julian oscillation mjo activity in the tropics however we find that ttt systems are statistically independent of the mjo i e they are equally liable to occur during any phase of the mjo three pcs out of five also show a significant association with el nino southern oscillation confirming that el nino years mostly coincide with suppressed convection at the intraseasonal time scales a result consistent with its impact on seasonal averages diagnosed in previous studies

tropical extratropical interactions over southern africa three cases of heavy summer season rainfall abstract the synoptic evolution of three tropical extratropical te interactions each responsible for extreme rainfall events over southern africa is discussed in detail along with the consideration of previously studied events common features of these heavy rainfall producing tropical temperate troughs ttts over southern africa are discussed it is found that 2 days prior to an event northeasterly moisture transports across botswana set up by the angola low are diverted farther south into the semiarid region of subtropical southern africa the ttts reach full maturity as a te cloud band rooted in the central subcontinent which is triggered by upper level divergence along the leading edge of an upper tropospheric westerly wave trough convection and rainfall within the cloud band is supported by poleward moisture transports with subtropical air rising as it leaves the continent and joins the midlatitude westerly flow it is shown that these systems fit within a theoretical framework describing

recurrent daily olr patterns in the southern africa southwest indian ocean region implications for south african rainfall and teleconnections a cluster analysis of daily outgoing longwave radiation olr anomalies from 1979 to 2002 over the southern africa southwest indian ocean swio region for the november to february season reveals seven robust and statistically well separated recurrent patterns of large scale organized convection among them are three regimes indicative of well defined tropical temperate interactions linking the hinterland parts of southern africa to the mid latitudes of the swio preferred transitions show a tendency for an eastward propagation of these systems analysis of daily rainfall records for south africa shows that six of the olr regimes are associated with spatially coherent and significant patterns of enhanced or reduced daily rainfall over the country atmospheric anomalies from the ncep doe ii reanalysis dataset show that the olr regimes are associated with either regional or near global adjustments of the atmospheric circulation the three regimes representative of tropical temperate interactions being in particular related to a well defined wave structure encompassing the subtropical and temperate latitudes featuring strong vertical anomalies and strong poleward export of momentum in the lee of the location of the cloud band the time series of olr regimes seasonal frequency are correlated to distinctive anomaly patterns in the global sea surface temperature field among which are shown to be those corresponding to el nino and la nina conditions the spatial signature of el nino southern oscillation s enso influence is related to the combination of an increased decreased frequency of these regimes it is shown in particular that the well known dipole in convection anomalies contrasting southern africa and the swio during enso events arises as an effect of seasonal averaging and is therefore not valid at the synoptic scale this study also provides a framework to better understand the observed non linearities between enso and the seasonal convection and rainfall anomalies over the region

african monsoon teleconnections with tropical ssts validation and evolution in a set of ipcc4 simulations a set of 12 state of the art coupled ocean atmosphere general circulation models oagcms is explored to assess their ability to simulate the main teleconnections between the west african monsoon wam and the tropical sea surface temperatures ssts at the interannual to multi decadal time scales such teleconnections are indeed responsible for the main modes of precipitation variability observed over west africa and represent an interesting benchmark for the models that have contributed to the fourth assessment report of the intergovernmental panel on climate change ipcc4 the evaluation is based on a maximum covariance analysis mca applied on tropical ssts and wam rainfall to distinguish between interannual and multi decadal variability all datasets are partitioned into low frequency lf and high frequency hf components prior to analysis first applied to hf observations the mca reveals two major teleconnections the first mode highlights the strong influence of the el nino southern oscillation enso the second mode reveals a relationship between the sst in the gulf of guinea and the northward migration of the monsoon rainbelt over the west african continent when applied to hf outputs of the twentieth century ipcc4 simulations the mca provides heterogeneous results most simulations show a single dominant pacific teleconnection which is however of the wrong sign for half of the models only one model shows a significant second mode emphasizing the oagcms difficulty in simulating the response of the african rainbelt to atlantic sst anomalies that are not synchronous with pacific anomalies the lf modulation of these hf teleconnections is then explored through running correlations between expansion coefficients ecs for ssts and precipitation the observed time series indicate that both pacific and atlantic teleconnections get stronger during the twentieth century the ipcc4 simulations of the twentieth and twenty first centuries do not show any significant change in the pattern of the teleconnections but the dominant enso teleconnection also exhibits a significant strengthening thereby suggesting that the observed trend could be partly a response to the anthropogenic forcing finally the mca is also applied to the lf data the first observed mode reveals a well known inter hemispheric sst pattern that is strongly related to the multi decadal variability of the wam rainfall dominated by the severe drying trend from the 1950s to the 1980s whereas recent studies suggest that this drying could be partly caused by anthropogenic forcings only 5 among the 12 ipcc4 models capture some features of this lf coupled mode this result suggests the need for a more detailed validation of the wam variability including a dynamical interpretation of the sst rainfall relationships

new constraints on the formation of the non volcanic continental galicia flemish cap conjugate margins numerous multichannel seismic data acquired on the starved continental margin off galicia show that the prominent intra crustal s reflector is observed only below the oceanward portion of the continental margin close to the ocean continent boundary superficial extension has been computed from the geometry of the well imaged tilted fault blocks of the entire margin by using a series of parallel seismic lines specifically designed for this purpose the pure shear model clearly accounts for the lithospheric extension of the continentward portion of the continental margin but not for the oceanward portion of the continental margin where the s reflector is present the s reflector is a detachment zone which presents a decreasing offset in the direction of the continent and this detachment zone has been active since the beginning of rifting recent kinematic reconstructions show that the conjugate margin to galicia is the southeastern flemish cap margin from the few seismic profiles available on this canadian margin a major master fault is observed beneath the continental slope and is interpreted as the outcropping portion of a main detachment zone identified on the galicia margin as the s reflector the proposed mechanism of extension for these two conjugate margins is pure shear which affects the whole lithosphere but in the upper part of the crust the rifting mechanism is either pure shear for the continentward portion of the galicia margin or simple shear for the oceanward portion of the galicia and the whole southeastern flemish cap margins where the detachment zone is active i consider that pure shear is the basic lithospheric mechanism and that simple shear is a mechanism which affects only the upper crust

cenozoic sequence stratigraphy of the central and northern north sea basin tectonic development sediment distribution and provenance areas the cenozoic succession in the central and northern north sea has been investigated to establish a regional sequence stratigraphic framework changes in sediment distribution indicate a complex pattern of regional vertical movements along older palaeozoic and mesozoic structures in cenozoic times these vertical movements mainly related to tectonic processes along the continental margin to the north and north west were responsible for the generation and removal of provenance areas for sediments delivered to the north sea basin through cenozoic time during the early through middle palaeogene sediments were mainly sourced from areas in the west and from the atlantic margin in the north uplift in the northern north sea in the late eocene was in the earliest oligocene followed by marked basin subsidence and tectonic uplift of southern norway a similar pattern of tectonic movements resulted in subaerial exposure of the northern north sea in the early miocene followed by significant tectonic subsidence in the basin and along the atlantic margin in late miocene pliocene times at the same time southern norway was uplifted and became a major sediment source after the miocene pliocene subsidence uplift events glacial processes in southern norway and fluvial processes in a large drainage area east and south east of the north sea were responsible for the main sediment influx to the north sea the cenozoic depositional sequences in the north sea developed in close interaction with regional tectonic movements and changes in provenance areas tectonic movements in north west europe overprinted global sea level changes so that the generation of depositional sequences and sequence boundaries apparently occurred independently of the rate of eustatic sea level change

cenozoic evolution of the eastern danish north sea this paper provides a review of recent high resolution and conventional seismic investigations in the eastern danish north sea and describes their implications for the development of the eastern north sea basin the results comprise detailed time structure maps of four major unconformities in the eastern danish north sea the top chalk surface mid paleocene near top oligocene the mid miocene unconformity and base quaternary the maps show that the eastern danish north sea has been affected by faulting and salt diapirism throughout the cenozoic carbonate mounds erosional valleys and pockmark or karst like structures were identified at the top of the upper cretaceous danian chalk group strike parallel erosional features and depositional geometries observed at near top oligocene and at the mid miocene unconformity indicate that these major sequence boundaries can be attributed to large scale lateral changes in sediment supply directions increases in sediment flux to the southeastern north sea at the eocene oligocene transition and in the post middle miocene appear to correlate with similar events world wide and with long term 18o increases indicating forcing by global factors i e eustasy and climate stratal geometries observed on the seismic data indicate that the so called neogene uplift of the eastern danish north sea may have been hundreds of metres less than previously suggested it is argued that late cenozoic uplift of the basin margin and of mountain peaks in southern norway may have been caused entirely by isostatic uplift of the crust in response to accelerated late cenozoic denudation and dissection of topography created in the paleogene the late cenozoic periods of accelerated denudation and incision rates were most likely driven by climatic deterioration and long term eustatic lowering rather than active late cenozoic tectonics the cause of which is conjectural a series of shallow thrust structures and an associated system of deep buried valleys were mapped thrust faulting most likely occurred in response to gravitational loading at the margin of an advancing ice sheet and it was followed by deep incision due to subglacial melt water erosion probably during the elsterian glaciation