evolution of strike slip duplexes and wrench related folding in the central part of al jabal al akhdar ne libya abstractthe deformation in the central part of al jabal al akhdar ne libya is dominated by e w right lateral strike slip fault zones that form a conjugate system with the n s left lateral strike slip faulting the dextral wrench dominated transpression is responsible for the formation of strike slip duplexes en echelon folds and thrusts that deform the cretaceous eocene sedimentary sequences the strike slip duplex is formed by the progressive linkage of horsetail like structures at the western tip of the al bayda strike slip fault that joined splays coming from other dextral strike slip faults the master linear fault branches into second order dextral or sinistral faults that regroup into a linear single fault faults started from arrays of en echelon extensional extensional shear fractures that then coalesced into throughgoing strike slip faults shortening was accompanied by significant n s striking left lateral strike slip displacements with the development of ne to ese and sw plunging major f

dynamics and thermodynamics of a warming event in a coupled tropical atmosphere ocean model abstract a simple coupled ocean atmosphere model similar to that of zebiak and cane is used to examine the dynamic and thermodynamic processes associated with el nino southern oscillation enso the model is run for 300 years the interannual variability which results is regular with a period of either 3 or 4 years quantized by the annual cycle the amplitude 1 5 m s 1 wind and 2 c sst anomalies period and structure of the interannual variability compare well with observations the model warm event is initiated in the spring prior to the event peak and is well described as an instability of the coupled system during instability growth the sea surface temperature sst anomaly is primarily generated by vertical upwelling processes the sst anomaly can be approximately described by the expression t t kth t where t is the sst anomaly t time h the upper layer thickness pycnocline perturbation and an effective damping time which includes heat loss to the atmosphere kt parameterizes

interannual variability in a tropical atmosphere ocean model influence of the basic state ocean geometry and nonlinearity abstract the behavior of a tropical coupled atmosphere ocean model is analyzed for a range of different background states and ocean geometries the model is essentially that of cane and zebiak for the tropical pacific except only temporally constant background states are considered here for realistic background states and ocean geometry the model solutions feature oscillations of period of 3 5 yr by comparing the full model solution with a linearized version of the model it is shown that the basic mechanism of the oscillation is contained within linear theory a simple linear analog model is derived that describes the nature of the interannual variability in the coupled tropical atmosphere ocean system the analog model highlights the properties that produce coupled atmosphere ocean instability in the eastern ocean basin and the equatorial wave dynamics in the western ocean basin that are responsible for a delayed negative feedback into this instability growth the growth rate of the local instabil

is enso a cycle or a series of events 1 after early ideas that saw el ninos as isolated events the advent of coupled models brought the conception of enso as a cycle in which each phase led to the next in a self sustained oscillation twenty two years of observations that represent the el nino and la nina peaks east pacific sst and the memory of the system zonal mean warm water volume suggest a distinct break in the cycle in which the coupled system is able to remain in a weak la nina state for up to two years so that memory of previous influences would be lost similarly while the amplitude of anomalies persists from the onset of a warm event through its termination there is no such persistence across the la nina break these observations suggest that el ninos are in fact event like disturbances to a stable basic state requiring an initiating impulse not contained in the dynamics of the cycle itself

equatorial pacific easterly wind surges and the onset of la nina events abstractthe processes responsible for the onset of la nina events have not received the same attention as those responsible for the onset of el nino events for which westerly wind events wwes in the tropical pacific have been identified as important contributors results here show that synoptic scale surface easterly wind surges ewss play an important role in the onset of la nina events akin to the role of wwes in the onset of el nino events it is found that ewss are a substantial component of zonal wind stress variance along the equatorial pacific using reanalysis wind stress fields validated against buoy measurements 340 ews events are identified between 1986 and 2012 their distributions in space time and el nino southern oscillation enso state are described about 150 ewss occur during enso neutral conditions during the months associated with la nina initiation and growth april december composites of changes in sea surface temperature anomaly ssta following these 150 events show s

westerly wind bursts and their relationship with intraseasonal variations and enso part ii energetics over the western and central pacific abstract the mechanism of synoptic scale eddy development in the generation of westerly wind bursts wwbs over the western central pacific and their relationship with the el nino southern oscillation enso and the madden julian oscillation mjo were examined in the wwb occurrences barotropic structures of equatorial eddy westerlies with cyclonic disturbances were found from the surface to the upper troposphere the dominant contributions to substantial eddy kinetic energy eke were the barotropic energy conversion kmke in the lower and middle tropospheres and the conversion from eddy available potential energy peke in the upper troposphere low frequency environmental westerlies centered near the equator preceded strong zonal convergence and meridional shear resulting in the substantial kmke the activation of synoptic convection also contributed to an increase in eke through peke these energies were redistributed to the lower equatorial troposphere through energy flux convergence gke the

recharge oscillator mechanisms in two types of enso the el ni oscillation enso tends to behave arguably as two different types or flavors in recent decades one is the canonical cold tongue type enso with major sea surface temperature anomalies ssta positionedoverthe easternpacific theotheris awarm pool typeensowith sstacenteredin the central pacific near the edge of the warm pool in this study the basic features and main feedback processes of these two types of enso are examined it is shown that the interannual variability of upper ocean heat content exhibits recharge discharge processes throughout the life cycles of both the cold tongue ct and warm pool wp enso types through a heat budget analysis with focus on the interannual frequency band the authors further demonstrate that the thermocline feedback plays a dominant role in contributing to the growth and phase transitions of both enso types whereas the zonal advective feedback contributes mainly to their phase transitions the westward shift of the ssta center of the wp enso and the presence of significant surface easterly wind anomalies over the far eastern equatorial pacific during its mature warm phase are the two main factors that lead to a reduced positive feedback for the eastern pacific ssta nevertheless both the wp and ct enso can be understood to a large extent by the recharge oscillator mechanism

absolute reconstructions of the paleozoic oceans abstract the orientation of three intraplate magmatic belts the mongolian from 130 to 280 m y south siberian from 320 to 400 m y and baltic from 365 to 400 m y belts which can be considered as hot spot tracks are used together with apparent paleomagnetic pole wander paths to reconstruct true motions of continents during paleozoic times the reconstructions obtained show that the old late precambrian pangea continued to exist in the early paleozoic with an inner arrangement of constituent continents strongly different from that of the late paleozoic pangea the continents were constantly located in the eastern hemisphere only the western hemisphere was occupied by the paleo pacific oceans four oceans existed in paleozoic times between the continents in the eastern hemisphere 1 the iapetus which originated in the late precambrian and closed before devonian times 400 m y 2 the asiatic paleo ocean which originated in the late precambrian and closed 450 m y ago 3 the uralian paleo ocean which opened around 500 m y ago and closed in the latest permian 240 230 m y 4 the paleo tethys which opened in the ordovician 480 450 m y and became the mesozoic tethys life duration of the oceans was 200 400 m y the main trend in the earth s evolution during the paleozoic was a break up of the old precambrian supercontinent and construction of the new late paleozoic pangea

age and structure of the southern rockall trough new evidence abstract the rockall trough separates the rockall plateau microcontinent from the shelf and slope west of the british isles the structure and age of the trough has been the source of considerable discussion although widely considered to be of oceanic origin postulated ages for the spreading range from permian to cretaceous new seismic profiles linked to the ipod sites in the bay of biscay and to oceanic anomalies of known age are used to present a new assessment of the age and structure of the southern rockall trough it is concluded that about 120 km of ocean crust is present in the trough and that spreading took place in the albian maastrichtian interval

slab breakoff insights from 3d thermo mechanical analogue modelling experiments abstract the detachment or breakoff of subducted lithosphere is investigated using scaled three dimensional thermo mechanical analogue experiments in which forces are measured and deformation is monitored using high speed particle imaging velocimetry piv the experiments demonstrate that the convergence rate in a subduction zone determine if and when slab detachment occurs slow subduction experiments with scaled convergence rates 1 cm yr 1 have lower peclet numbers and are characterized by lower tensile strength subducted lithosphere causing detachment to occur when the downward pull force exerted by a relatively short subducted slab is relatively low therefore when continental collision is preceded by slow oceanic subduction the hot and weak subducted lithosphere need not be very long or extremely negatively buoyant to cause detachment under such conditions detachment may occur sooner after the onset of continental subduction than previously predicted in contrast if collision is preceded by rapid subduction 10 cm yr 1 breakoff will be delayed and occur only when the convergence rate has slowed sufficiently to thermally weaken the slab and cause its eventual failure the analogue experiments further confirm that slab detachment occurs diachronously as it propagates along the plate boundary stereoscopic piv reveals a characteristic strain pattern that accompanies the detachment horizontal contraction and subsidence with scaled values up to 1200 m in the trench and forearc area precedes the passage of the detachment and is followed by horizontal extension and uplift up to 900 m high frequency monitoring captures rapid propagation of the detachment along the plate boundary at scaled rates of up to 100 cm yr 1 however this rate is not constant and interaction between the slab and lower mantle or opening of a backarc basin in the upper plate can reduce or stop slab breakoff propagation altogether

facies patterns and subsidence history of the jumilla cieza region southeastern spain abstract a detailed analysis of the facies patterns and subsidence history since the late cretaceous 100 ma of the jumilla cieza region in southeastern spain has implications for the debate on the mechanisms causing third order changes in sea level the local subsidence history shows periods characterized by specific trends in tectonic subsidence each with a typical concomitant facies pattern the successive periods are considered to illustrate the transition of the southern iberian plate boundary from a passive margin 108 40 ma through an extensional phase 40 20 ma to a thrust and fold belt 20 ma to recent timing and changes in relative sea level derived from the sedimentary record closely match with the regional tectonic events the order of magnitude of these sea level changes exceed those predicted by the global curve therefore we suggest that in the studied area third order sea level fluctuations are of relatively minor magnitude and only enhance the effect of tectonic induced vertical movements

contrasting eastern pacific and central pacific types of enso abstract surface observations and subsurface ocean assimilation datasets are examined to contrast two distinct types of el nino southern oscillation enso in the tropical pacific an eastern pacific ep type and a central pacific cp type an analysis method combining empirical orthogonal function eof analysis and linear regression is used to separate these two types correlation and composite analyses based on the principal components of the eof were performed to examine the structure evolution and teleconnection of these two enso types the ep type of enso is found to have its sst anomaly center located in the eastern equatorial pacific attached to the coast of south america this type of enso is associated with basinwide thermocline and surface wind variations and shows a strong teleconnection with the tropical indian ocean in contrast the cp type of enso has most of its surface wind sst and subsurface anomalies confined in the central pacific and tends to onset develop and decay in situ

an advective reflective conceptual model for the oscillatory nature of the enso recent findings about zonal displacements of the pacific warm pool required a notable modification of the delayed action oscillator theory the current leading theory for the el nino southern oscillation enso simulations with a linearized coupled ocean atmosphere model resulted in 3 to 6 year enso like oscillations with many of the variable model parameters found to be very close to their observed values this simple model suggests that ocean processes that are ignored or underestimated in the delayed action oscillator theory such as zonal current convergence zonal advection of sea surface temperature and equatorial wave reflection from the eastern ocean boundary are fundamental to the development of the enso in particular to its manifestations in the central equatorial pacific

phase transition of the el nino southern oscillation a stationary sst mode a stationary sst mode is proposed to understand the physical mechanisms responsible for the phase transition of the el nino southern oscillation this stationary sst mode differs from the original delayed oscillator mode and the slow sst mode in the sense that it considers both balanced and unbalanced thermocline depth variations and does not take into account the zonal propagation of sst within this mode the walker circulation acts as a positive feedback mechanism to amplify and maintain an existing interannual sst anomaly whereas the hadley circulation acts as a negative feedback mechanism that dismisses the original anomaly and causes the phase shift from a warm cold to a cold warm episode the key to the cause of interannual oscillations in the stationary sst mode lies in the zonal mean thermocline depth variation that is not in equilibrium with the winds because of the nonequilibrium this part of the thermocline depth anomaly tends to have a phase lag with the wind or sst anomaly and therefore holds a key for the interannual oscillation the zonally asymmetric part of the thermocline depth anomaly on the other hand is always in sverdrup balance with the winds such a phase relationship agrees well with observations and with gcm simulations the stationary sst mode strongly depends on the basin width on the air sea coupling strength and on the seasonal cycle basic state for a reasonable parameter regime it depicts an interannual oscillation with a period of 2 7 years this stationary sst mode is also season dependent it has a maximum growth rate during the later part of the year and a negative growth rate during the northern spring which may explain the occurrence of the mature phases of the el nino in the northern winter and a rapid drop of the lagged correlation of the southern oscillation index in the boreal spring

a north sea southern norway seismic crustal profile summary in this paper results are presented from a seismic refraction experi ment canobe carried out in southern norway ten explosions fired at sea were recorded on land by shifting 13 recording instruments along a pro file with an average station spacing of 5 km the main line runs in a north easterly direction from the south coast at lista along the western margin of the oslo graben into the norsar array with a total length of 5 15 km a separate leg runs across the graben just north of oslo for the first time allow ing a direct comparison of seismic records in the graben with those in the adjacent precambrian shield area the laterally varying crustal structure along the profile is examined by modelling of travel times and amplitudes of p wave arrivals the moho which is the major discontinuity in the lowermost crust appears to sink beneath the coast from 27 km on the seaward side to 34 km onshore the two dimensional modelling procedure adopted proves invaluable in explaining the characteristic amplitude pattern observed in this area beyond the coastal area our picture of the crust is that of a relatively homogeneous one as expected for a shield area there are no indications of significant discontinuities in the crust along the first 300 km of the profile although from the large pg amplitudes within this distance range we infer a strong velocity gradient in the lower crust two structural models are pro posed for the oslo graben where the moho appears to be elevated to between 25 and 29 km

early history of the atlantic ocean and gas hydrates on the blake outer ridge results of the deep sea drilling project leg 76 leg 76 of the deep sea drilling project achieved two major scientific objectives the first objective was met at site 533 where on the blake outer ridge gas hydrates were identified by geophysical geochemical and geological studies gas hydrate decomposition produced a volumetric expansion of 20 1 of gas volume to pore fluid volume this expansion exceeded by about a factor of four the volume of gas that could be released from solution in pore water under similar conditions the gas hydrate includes methane ethane propane and isobutane but apparently excluded normal butane and higher molecular weight hydrocarbons as predicted from gas hydrate crystallography for the first time marine gas hydrates were tested with a pressure core barrel the second objective was achieved when coring at site 534 in the blake bahama basin sampled the oldest oceanic sediments yet recovered the sequence of oceanic basement and overlying sediments documents the geologic history of the early stages of the opening of the north atlantic ocean in detail the oldest oceanic sediments are red claystones and laminated green and brown claystones of middle callovian age this finding supports the interpretation that the beginning of the modern north atlantic occurred in the early callovian 155 m y b p as much as 20 m y later in time than often previously thought

large scale strike slip displacement of the drauzug and the transdanubian mountains in early alpine history evidence from permo mesozoic facies belts abstract both the drauzug italy austria and the transdanubian mountains hungary show great differences in facies compared to the geological units that presently surround them i e proximal facies contrast with distal facies in the permo triassic lower liassic strata in the drauzug and the transdanubian mountains indicate an extensional regime causing typical structural features such as tilted blocks fault scarps and drowned carbonate platforms the permo mesozoic facies zones provide markers for the paleogeographic fitting of the drauzug and the transdanubian mountains with areas today lying some 300 400 km to the west the drauzug corresponds to the lombardian basin and the westernmost part of the northern calcareous alps while the transdanubian mountains correspond to the westernmost part of the lombardian basin the trento platform and the belluno trough the drauzug and the transdanubian mountains together with the south alpine realm were displaced to the east along strike slip faults during the middle jurassic to early cretaceous opening of the central atlantic and ligurian piemont oceans and the simultaneous subduction of the vardar ocean at the eastern margin of apulia finally in late oligocene and miocene times the southern alps were displaced back to the west along the dextral periadriatic fault system

early opening history of the north atlantic i structure and origin of the faeroe shetland escarpment summary marine geophysical surveys show that the escarpment is the buried feather edge of a thick pile of flood basalts of early eocene age overlying a thinner more widespread layer of basalts of late palaeocene age the escarpment does not therefore define the continent ocean boundary in the southern norwegian sea but instead marks the contemporary shoreline separating terrestrially erupted basalt flows in the north from a restricted shallow water shelf to the south the basalts overlie 5 6 km of mesozoic sediments which have completely buried a large conical flat topped seamount of similar dimensions to anton dohrn and rosemary bank we call this newly postulated body the brendan seamount the mesozoic sediments are at least as old as early cretaceous in age therefore precluding the possibility that the mid cretaceous seafloor spreading episode supposed by some to have created the rockall trough could have also created the thin crust inferred to underlie the faeroe shetland trough and mbre basin

volcanic belts as markers of the mesozoic cenozoic active margin of eurasia abstract from the triassic to the present linear belts of calc alkaline volcanism developed along the southern margin of eurasia in the triassic the calc alkaline belt can be traced in turan fore caucasus crimea and dobrogea its development is related to the closure of the paleo tethys when fragments of gondwana iran afghanistan etc were approaching eurasia since the early jurassic calc alkaline volcanism has been related to subduction of the oceanic crust of the mesozoic tethys five stages of calc alkaline volcanic activity can be distinguished early jurassic middle jurassic early cretaceous late cretaceous paleogene and late miocene quaternary the configuration of the volcanic belts the intensity of the volcanism and the chemistry of the erupted products change considerably from stage to stage mesozoic belts were most pronounced in the pontian transcaucasian segment of the margin starting from the late cretaceous and especially in the cenozoic the volcanic belts can be continuously traced from the balkans to afghanistan most of the belts were actually island arcs formed on the fragments of the hercynian of baikalian basement and in this respect similar to the island arc of japan only the incipient island arcs of senonian age formed close to the passive margin of gondwana are the exceptions they were built on oceanic crust and are geochemically close to the mariana arc at certain times early jurassic eocene parallel chains of island arcs existed in general the situation resembled the present day convergent boundary in the western pacific as closure of the tethys proceeded island arcs gave way to marginal continental volcanic belts with wide spread development of high potassium particularly shoshonitic series peaks of volcanic activity in the bajocian late cretaceous eocene and late miocene present alternated with quiet periods and corresponded to the times when the convergence rate between africa and eurasia increased the opening of the back arc basins is reflected in outbursts of basaltic rift type volcanism these outbursts occurred in the toarcian aalenian bathonian late jurassic aptian turonian and early middle eocene

the role of reversed equatorial zonal transport in terminating an enso event abstractthis study shows the sudden basinwide reversal of anomalous equatorial zonal transport above the thermocline at the peaking phase of enso triggers rapid termination of enso events the anomalous equatorial zonal transport is controlled by the concavity of anomalous thermocline meridional structure across the equator during the developing phase of enso opposite zonal transport anomalies form in the western central and central eastern equatorial pacific respectively both are driven by the equatorial thermocline anomalies in response to zonal wind anomalies over the western central equatorial ocean at this stage the anomalous zonal transport in the east enhances enso growth through zonal sst advection in the mature phase of enso off equatorial thermocline depth anomalies become more dominant in the eastern pacific because of the reflection of equatorial signals at the eastern boundary as a result the meridional concavity of the thermocline anomalies is reversed in the east this change reve

the newfoundland basin ocean continent boundary and mesozoic seafloor spreading history the ocean continent boundary in the newfoundland basin is defined as the seaward limit of a continental margin magnetic smooth zone east of the grand banks this boundary is marked by a prominent nne trending magnetic anomaly that is correlated with the j anomaly 115 m y south of flemish cap the smooth zone boundary strikes approximately 060 and is approximately 15 m y younger magnetic anomaly trends suggest two directions of motion during separation of iberia and north america the first phase of motion commencing at j anomaly time with a spreading center strike of 015 produced a rifted margin along the grand banks south of the newfoundland seamounts no spreading occurred north of the seamounts during this phase implying a counter clockwise rotation of iberia and no grand banks galicia bank separation the second phase began at about 102 m y with a shift of the pole of rotation to a location near paris producing a ridge orientation of approximately 060 this spreading center extended north and east into the northern newfoundland basin and bay of biscay producing a rifted margin south of flemish cap and opening of biscay this ridge geometry produced a component of extension across the newfoundland fracture zone and the southeastward migration of the resultant leaky transform fault between 102 m y and the next pole shift produced the volcanic edifice of the southeast newfoundland ridge fracture zone trends during this phase also exerted strong control on volcanism within the newfoundland seamount province this activity ceased at about 97 m y the date at which the second phase ended is not well defined by presently available data a rrr triple junction existed in the northeastern newfoundland basin western biscay region for a short time prior to anomaly33 34 80 m y which marks the inception of a continuous mid atlantic ridge spreading center between the newfoundland and charlie gibbs fracture zones

tectonic evolution of the north sea basin crustal stretching and subsidence summary the lithospheric stretching model for the formation of sedimentary basins was tested in the central north sea by a combined study of crustal thinning and basement subsidence patterns a profile of crustal structure was obtained by shooting a long range seismic experiment across the central graben the main axis of subsidence a seabed array of 12 seismometers in the graben was used to record shots fired in a line 530 km long across the basin the data collected during the experiment were interpreted by modelling synthetic seismograms from a laterally varying structure and the final model showed substantial crustal thinning beneath the graben subsidence data from 19 exploration wells were analysed to obtain subsidence patterns in the central north sea since jurassic times changes in water depth were quantified using foraminiferal assemblages where possible and observed basement subsidence paths were corrected for sediment loading compaction and changes in water depth through time the seismic model is shown to be compatible with the observed gravity field and the small size of observed gravity anomalies is used to argue that the basin is in local isostatic equilibrium both crustal thinning and basement subsidence studies indicate about 70 km of stretching across the central graben during the mid jurassic to early cretaceous extensional event this extension appears to have occurred over crust already slightly thinned beneath the graben and the seismic data suggest that total extension since the early permian may have been more than 100km the data presented here may all be explained using a simple model of uniform extension of the lithosphere

mid holocene climate and land sea interaction along the southern coast of saurashtra western india abstract the relict mudflat from the southern saurashtra coast of gujarat was investigated using geochemical and palynological analyses supported by radiocarbon dating to understand whether climate fluctuations and sea level operated in tandem during mid holocene the study revealed that the saurashtra coast experienced relatively wet climatic conditions with simultaneous occurrence of marginally high sea level between 4710 and 2825 cal yr bp subsequently a gradual onset of aridity and lowering of the sea level was observed between 2825 and 1835 cal yr bp and further a slight decrease in aridity is observed after 1835 cal yr bp the present day coastal configuration was probably achieved after around 1500 cal yr bp considering the tectonic instability of saurashtra coast land level changes the effective mid holocene sea level was estimated to be 1 m higher than the present the study demonstrates that sea level changes climate variability and land level changes were coupled during the mid holocene

observed relationships between oceanic kelvin waves and atmospheric forcing abstract the madden julian oscillation mjo has been implicated as a major source of the wind stress variability that generates basin scale kelvin waves in the equatorial pacific one source of debate concerning this relationship is the apparent difference in the frequencies of the two processes this work utilizes data from the tropical atmosphere ocean tao array of moored buoys along with outgoing longwave radiation data to show by means of a multiple linear regression model and case studies that the frequency discrepancy is due to a systematic decrease in the phase speeds of the kelvin waves and an increase in the period of the waves toward the east as conditions adjust toward el nino among the potential contributing factors to this phase speed decrease is an apparent air sea interaction that enhances the wind forcing of some of the kelvin waves allowing them to continue to amplify because the propagating wind stress anomaly decelerates to the speed of the developing kelvin wave instead of the sig

modulation of westerly wind bursts by sea surface temperature a semistochastic feedback for enso abstract westerly wind bursts wwbs in the equatorial pacific are known to play a significant role in the development of el nino events they have typically been treated as a purely stochastic external forcing of enso recent observations however show that wwb characteristics depend upon the large scale sst field the consequences of such a wwb modulation by sst are examined using an ocean general circulation model coupled to a statistical atmosphere model i e a hybrid coupled model an explicit wwb component is added to the model with guidance from a 23 yr observational record the wwb parameterization scheme is constructed such that the likelihood of wwb occurrence increases as the western pacific warm pool extends a semistochastic formulation which has both deterministic and stochastic elements the location of the wwbs is parameterized to migrate with the edge of the warm pool it is found that modulation of wwbs by sst strongly affects the characteristics of enso in particular coupled fe

combined role of high and low frequency processes of equatorial zonal transport in terminating an enso event abstractthis study investigates the sudden reversal of anomalous zonal equatorial transport above thermocline at the peak phase of enso the oceanic processes associated with zonal transport are se

the march 1997 westerly wind event and the onset of the 1997 98 el nino understanding the role of the atmospheric response in a previous study the effect of the march 1997 westerly wind event wwe on the evolution of the tropical pacific ocean was studied using an ocean general circulation model gcm the response was characterized by i a cooling of the far western pacific 0 88c ii a rapid eastward displacement of the warm pool 2000 km in a month and iii a weak warming of the central eastern pacific along the path of the oceanic kelvin wave excited by the wwe 0 58c in this study the atmospheric response to these aspects of the sea surface temperature sst response are investigated using an atmospheric gcm forced with the sst anomalies from the ocean only experiments the results have demonstrated that the three aspects of the sst anomaly field generated by the wwe

new paleomagnetic results from cretaceous sediments near lisboa portugal and implications for the rotation of iberia abstract paleomagnetic study of outer platform sediments of late jurassic early cretaceous age from portugal lisboa area leads to characteristic remanent magnetization directions for the hauterivian barremian d 317 i 58 and the aptian d 344 i 47 the absolute rotation of iberia between 125 and 110 ma is consequently of about 27 in an anticlockwise sense a later rotation of about 14 follows the first one in the same sense from 110 ma the total absolute rotation of iberia from the hauterivian age determined by paleomagnetism is thus about 41 the comparison of declinations measured with paleodeclinations calculated in lisboa from the eurasian and african poles of similar age indicates that the main phase of relative rotation of iberia with respect to eurasia occurs during the first stage of relative motion i e hauterivian to aptian the tectonic history of the bay of biscay is in good agreement with these two stages of rotation the total relative rotation with respect to europe is 34 this value is consistent with results previously established by van der voo 2 3 25 but we have established that the main phase of rotation 30 occurs in the hauterivian aptian interval the movement of iberia is clearly linked to the movement of africa in direction and age but the amount of rotation of iberia during the early cretaceous is much larger and implies that iberia was not a real part of the african plate

short term environmental changes in the cretaceous tethyan ocean micropalaeontological evidence from the early albian oceanic anoxic event 1b to better understand the linkage between climate and ocean circulation under greenhouse conditions we have studied calcareous nannofossils palynomorphs and benthic foraminifera from the early albian oceanic anoxic event 1b black shale oae 1b in the vocontian basin se france we propose that monsoonal activity resulting from precessional forcing and modulated by eccentricity driven temperature changes represents the driving factor of oae 1b formation in low latitudes with the onset of oae 1b increasingly warm and humid conditions stronger winds and enhanced terrestrial input led to higher surface water productivity therefore increased productivity is an important factor for oae 1b formation in the vocontian basin however monsoonally forced productivity changes are a regional climate signal only the supraregional occurrence of the oae 1b is probably due to a reduction of deep water formation in the low latitudes under extremely warm and humid conditions leading to enhanced preservation of organic matter

tectonic paleostress fields and structural evolution of the nw caucasus fold and thrust belt from late cretaceous to quaternary abstract the nw caucasus fold and thrust belt essentially corresponds to the inverted western flysch zone of the great caucasus mountains a deep basin that developed from late jurassic to eocene times between the scythian plate to the north and the transcaucasian terranes to the south the shatsky ridge sw of the nw caucasus zone the flysch basin was strongly affected by compression in late eocene times when the characteristic wnw trending folds and thrusts of the nw caucasus belt developed some authors regard the main compressive deformation as miocene in age by means of remote sensing analysis we elucidate the geometry of major structures in the belt wnw trending south vergent thrusts and folds and major vertical and transverse nne ssw to ne sw deep fault zones the later structures are interpreted as ancient faults that were active during the development of the flysch basin paleostress investigations reveal seven main tectonic episodes in the evolution of the nw caucasus since late cretaceous combining structural interpretation remote sensing analysis and paleostress field reconstruction we propose a model for the structural evolution of the belt during the late cretaceous paleocene the western caucasus zone was under transtensional regime with an e w to ne sw trending 3 that generated oblique normal movements along nne ssw transverse faults and wnw ese margins of the flysch basin this tectonism could correspond to rifting related to the formation of the eastern black sea basin at the paleocene eocene boundary a transpressional event with an e w to nw se trending 1 developed and the nne ssw to ne sw trending faults could have been inverted this event could correspond to an attenuation in the eastern black sea basin formation or to the incipient accretion of the transcaucasian terranes during the eocene another e w to nw se oblique extension transtensional event affected the flysch basin that could be related to a known rifting phase in the eastern black sea basin strong nne ssw to ne sw compression characterises late eocene tectonism the fold and thrust belt developed at this time as a result of the direct collision of the shatsky ridge with the scythian plate a ne sw extension followed the late eocene event related to basin development around the newly formed fold belt a wnw ese oblique contraction affected the belt during the early miocene as the result of arabian plate convergence with the caucasian system the latest inferred event is a compressional regime with nnw sse trending 1 that is affecting the nw caucasus belt from sarmatian times until the present under this oblique compression the belt has deformed as in a dextral shear zone and the thrust surfaces have acquired lenticular shapes this study highlights the occurrence of oblique movements in the nw caucasus area prior to and after the dominant late eocene compression from the late cretaceous until the eocene the structural development of the nw caucasus was closely related to the evolution of the eastern black sea basin from the late eocene until quaternary times it was rather related to the arabia eurasia plate convergence

paleomagnetic implications on the evolution of the tethys belt from the atlantic ocean to the pamirs since the triassic abstract we first re examined the apparent polar wander curves for stable eurasia and africa since the triassic these curves were then combined together with curves of north and south america according to the kinematics of the atlantic ocean and a synthetic polar wander curve was given then most of the paleomagnetic results from the tethys mobile belt from the atlantic to the pamirs were analysed several groups of plates microplates and blocks can be seen first relatively stable regions like maghreb and sicily which have not moved much then we have a group formed by iberia sardinia italy and to a lesser extent corsica and the western and central alps for these blocks movements are anticlockwise rotations chiefly driven by the anticlockwise rotation of africa but they are sometimes stronger to the east a major change takes place the north of the aegean sea and the ionian zone are clockwise rotated and these rotations are recent oligocene miocene for the first part pliocene to the present for the second part a major problem arises in turkey caucasus and iran paleomagnetic results indicate a position far to the south of eurasia and at the same time geological evidence is in favour of a position close to eurasia we discuss these discrepancies

el nino modoki and its possible teleconnection 1 using observed data sets mainly for the period 1979 2005 we find that anomalous warming events different from conventional el nino events occur in the central equatorial pacific this unique warming in the central equatorial pacific associated with a horseshoe pattern is flanked by a colder sea surface temperature anomaly ssta on both sides along the equator empirical orthogonal function eof analysis of monthly tropical pacific ssta shows that these events are represented by the second mode that explains 12 of the variance since a majority of such events are not part of el nino evolution the phenomenon is named as el nino modoki pseudo el nino modoki is a classical japanese word which means a similar but different thing the el nino modoki involves ocean atmosphere coupled processes which include a unique tripolar sea level pressure pattern during the evolution analogous to the southern oscillation in the case of el nino hence the total entity is named as el nino southern oscillation enso modoki the enso modoki events significantly influence the temperature and precipitation over many parts of the globe depending on the season the impacts over regions such as the far east including japan new zealand western coast of united states etc are opposite to those of the conventional enso the difference maps between the two periods of 1979 2004 and 1958 1978 for various oceanic atmospheric variables suggest that the recent weakening of equatorial easterlies related to weakened zonal sea surface temperature gradient led to more flattening of the thermocline this appears to be a cause of more frequent and persistent occurrence of the enso modoki event during recent decades

thinned and subsided continental crust on the rifted margin of eastern canada crustal structure thermal evolution and subsidence history summary seismic refraction measurements were carried out using ocean bottom seismometers over foundered continental crust in orphan basin and flemish pass on the continental margin north east of newfoundland tau p travel time inversion synthetic seismogram analysis and conventional layered model calculations were applied to the data the results show that these outer regions of the margin are underlain by thinned continental crust with a total depth to the m discontinuity of about 22 km there are two main crustal layers with p velocities of about 6 1 and 7 0 km s 1 which appear to be homogenous and separated by sharp interfaces these are overlain by a layer in which p velocities are about 5 5 km s 1 this is interpreted to be precambrian or palaeozoic basement mesozoic and cenozoic sediments cover the basement rocks and are over 4 km thick the results imply that crustal thinning to about 50 per cent of the original crustal thickness occurred the gravity anomaly data show that the thin crust has a maximum horizontal extent of about 450 km from the ocean continent boundary near orphan knoll landward to the outer continental shelf the subsidence history and thermal evolution of the region was computed assuming that the observed thinning is produced by horizontal extension of the lithosphere it is suggested that extension can only satisfy the observed crustal structure and elevation of the margin during the rift phase if more extension took place in the lower lithosphere than in the upper lithosphere the computed subsidence is compared to the observed subsidence and the total amounts of subsidence are similar however the shape of the observed subsidence curves measured in deep exploratory wells differs significantly from the predicted subsidence assuming cooling began when final continental breakup occurred in the late cretaceous the temperature distribution within the lithosphere due to extension may be related to the flexural rigidity of the plate as a function of both time and position across the margin therefore it is suggested that the response of the lithosphere to sediment loading and the large amplitude of the gravity shelf edge anomalies are directly related to the thermal history of the region

palaeotectonic reconstruction of the central alpine mediterranean belt for the neogene abstract the structural patterns of the central alpine mediterranean belt ranging from the eastern balearic sea to the western aegean sea have been reconstructed for 10 and 20 ma b p they have been obtained in the frame of the africa europe convergence through a step by step rigid plastic reconstruction using available geological and palaeomagnetic data all domains outlined in the present situation are shown in the palaeotectonic reconstructions while the structural pattern at 10 ma b p is similar to that of the present except for the tyrrhenian region that at 20 ma b p differs from it in most areas the well known adriatic promontory of the african plate is recognizable in both pictures and at 20 ma its original boundaries are revealed as strongly deformed flysch belts the adriatic promontory was broken up in the early or middle miocene into two microplates of comparable sizes the norther one is the adriatic microplate s s which suffered counter clockwise rotation by 20 relative to africa around the alpine apenninic whirl centre the southern one is the apulian microplate first outlined in the present work including the south apenninic and the apulian s s south of the gargano peninsula platforms which suffered no rotations relative to africa but which moved towards the northeast of it the primary reason for the break up of the adriatic promontory was most probably the opening of the balearic ligurian sea since 10 ma the adriatic and apulian microplates were again integral with africa or perhaps they moved towards the west relative to africa pushed by the turkish microplate the orogeny in the area discussed is mostly linked with collisional processes on the boundaries of the adriatic apulian unit

triggering of el nino by westerly wind events in a coupled general circulation model two ten members ensemble experiments using a coupled ocean atmosphere general circulation model are performed to study the dynamical response to a strong westerly wind event wwe when the tropical pacific has initial conditions favourable to the development of a warm event in the reference ensemble cref no wind perturbation is introduced whereas a strong westerly wind event anomaly is introduced in boreal winter over the western pacific in the perturbed ensemble cwwe our results demonstrate that an intense wwe is capable of establishing the conditions under which a strong el nino event can occur first it generates a strong downwelling kelvin wave that generates a positive sea surface temperature sst anomaly in the central eastern pacific amplified through a coupled ocean atmosphere interaction this anomaly can be as large as 2 5 c 60 days after the wwe secondly this wwe also initiates an eastward displacement of the warm pool that promotes the occurrence of subsequent wwes in the following months these events reinforce the initial warming through the generation of additional kelvin waves and generate intense surface jets at the eastern edge of the warm pool that act to further shift warm waters eastward the use of a ten members ensemble however reveals substantial differences in the coupled response to a wwe whereas four members of cwwe ensemble develop into intense el nino warming as described above four others display a moderate warming and two remains in neutral conditions this diversity between the members appears to be due to the internal atmospheric variability during and following the inserted wwe in the four moderate warm cases the warm pool is initially shifted eastward following the inserted wwe but the subsequent weak wwe activity when compared to the strong warming cases prevents to further shift the warm pool eastwards the seasonal strengthening of trade winds in june july can therefore act to shift warm waters back into the western pacific reducing the central eastern pacific warming this strong sensitivity of the coupled response to wwes may therefore limit the predictability of el nino events as the high frequency wind variability over the warm pool region remains largely unpredictable even at short time lead

kinematic evolution of the tethys belt from the atlantic ocean to the pamirs since the triassic abstract we present an updated series of kinematic reconstructions of the major plates around the tethys from the atlantic ocean to the pamirs between the early jurassic and the present this set is used elsewhere as a basis for paleogeographic maps of the entire region the problems related to the positions of the continents in the lower triassic are also discussed no direct analyses of magnetic anomalies and fracture zones in the atlantic have been made rather all available poles and rotations have been tested in order to eliminate or minimize possible kinematic errors the reconstructions are shown for nine key geological periods which correspond to well recognized magnetic anomalies except for the jurassic cretaceous boundary and the cretaceous tertiary boundary which correspond to interpolated positions paleolatitudes have been drawn using the study of westphal et al 1986 an attempt has been made to take into account the displacements caused by formation of the continental margins and basins by stretching the resulting relative vector of motions along the northern boundary of the tethys shows a significant change 80 m y ago left lateral motion with compression dominates before whereas right lateral motion with compression dominates after to the east rates of motion vary by a factor of three with time and four maxima can be clearly related to tectonic events in the late jurassic late cretaceous eocene and post middle miocene to the west north of apulia on the contrary the motion rate has not changed significantly since the early cretaceous and is close to 1 cm yr as an average these rather complex adjustments in rates and directions of relative motion are produced in great part through a complex migration of the africa eurasia pole of rotation and seem to be mostly governed by the tectonics of the tethys plate boundary

westerly wind bursts enso s tail rather than the dog westerly wind bursts wwbs in the equatorial pacific occur during the development of most el nino events and are believed to be a major factor in enso s dynamics because of their short time scale wwbs are normally considered part of a stochastic forcing of enso completely external to the interannual enso variability recent observational studies however suggest that the occurrence and characteristics of wwbs may depend to some extent on the state of enso components implying that wwbs which force enso are modulated by enso itself satellite and in situ observations are used here to show that wwbs are significantly more likely to occur when the warm pool is extended eastward based on these observations wwbs are added to an intermediate complexity coupled ocean atmosphere enso model the representation of wwbs is idealized such that their occurrence is modulated by the warm pool extent the resulting model run is compared with a run in which the wwbs are stochastically applied the modulation of wwbs by enso results in an enhancement of the slow frequency component of the wwbs this causes the amplitude of enso events forced by modulated wwbs to be twice as large as the amplitude of enso events forced by stochastic wwbs with the same amplitude and average frequency based on this result it is suggested that the modulation of wwbs by the equatorial pacific sst is a critical element of enso s dynamics and that wwbs should not be regarded as purely stochastic forcing in the paradigm proposed here wwbs are still an important aspect of enso s dynamics but they are treated as being partially stochastic and partially affected by the large scale enso dynamics rather than being completely external to enso it is further shown that wwb modulation by the large scale equatorial sst field is roughly equivalent to an increase in the ocean atmosphere coupling strength making the coupled equatorial pacific effectively self sustained

spring persistence transition and resurgence of el nino we present a systematic exploration of differences in the spatiotemporal sea surface temperature sst evolution along the equatorial pacific among observed el nino events this inter el nino variability is captured by two leading orthogonal modes which explain more than 60 of the interevent variance the first mode illustrates the extent to which warm sst anomalies sstas in the eastern tropical pacific ep persist into the boreal spring after the peak of el nino our analysis suggests that a strong el nino event tends to persist into the boreal spring in the ep whereas a weak el nino favors a rapid development of cold sstas in the ep shortly after its peak the second mode captures the transition and resurgence of el nino in the following year an early onset el nino tends to favor a transition to la nina whereas a late onset el nino tends to persist long enough to produce another el nino event the spatiotemporal evolution of several el nino events during 1949 2013 can be efficiently summarized in terms of these two modes which are not mutually exclusive but exhibit distinctive coupled atmosphere ocean dynamics

the transition from passive to active margin tectonics a case study from the zone of samedan eastern switzerland the zone of samedan is part of a fossil early mesozoic rift system originally situated in the distal lower austro alpine domain of the adriatic passive continental margin an early mesozoic configuration of asymmetrical rift basins bounded by relative structural highs compartmentalized late cretaceous active margin tectonics jurassic half grabens were folded into arcuate synclines whereas relative structural highs engendered thin imbricated thrust sheets west directed thrusting and folding initiated at the surface and continued to depths favoring mylonitization under lower greenschist facies conditions at this time liguria piemontese ophiolites were accreted to lower austro alpine units directly underlying the zone of samedan late cretaceous orogenic collapse of the adriatic active margin involved the reactivation of west directed thrusts as low angle top to the east normal faults these faults accommodated extensional uplift of liguria piemontese ophiolites and lower austro alpine units beneath and within the zone of samedan during paleogene collision some late cretaceous faults in the zone of samedan were reactivated under lower anchizonal conditions as north directed thrusts the latter stages of this early tertiary thickening were transitional to brittle high angle normal faulting associated with top to the east extension and spreading above the warm uplifting lepontine dome

structure and evolution of the passive margin of the eastern tethys abstract an extensive passive margin was formed in the triassic along the periphery of arabia including the tauric carbonate platform this event is related to the opening of the mesozoic tethys when a number of microcontinents split off from gondwana triassic extension and continental rifting resulted in the formation of a structural pattern which is uniform from the dinarides to oman it includes the following elements 1 1 shelf 2 2 continental slope 3 3 deep basin probably with a floor of attenuated sialic crust 4 4 inner carbonate platform in the jurassic cretaceous stable conditions prevailed influenced only by eustatic oscillations of the sea level turbidites accumulated on the continental rise while cherts and radiolarites were deposited in the deep basins hawasina pichakun antalya pindus below the ccd level sedimentation on the shelf was controlled by north northeast transverse tectonic elements which also continued across the passive margin dividing it into a number of segments collision with an island arc led to obduction of the oceanic crust deformation of the passive margin and overthrusting of its sedimentary cover onto the arabian shelf obduction and deformation lasted for about 10 m y and created a new tectonic pattern with concentric structural zones surrounding the arabian promontory these zones include 1 1 the flysch basin a remnant of the closing tethys 2 2 an uplift a site of periodical emergence and erosion corresponding to the frontal part of the ophiolitic nappes 3 3 the border furrow a depocenter of low energy calcareous marls 4 4 the arabian shield constantly emerged during the tertiary tectonic deformation of these zones caused by the collision of arabia with eurasia began prior to the early miocene and it is still going on data on afghanistan demonstrate that its central part the gelmend argandab and kabul blocks belonged during the paleozoic and early mesozoic to the continental shelf of india

geoid pangea and convection abstract we show that the present geoid has a simple low order configuration with an axis of symmetry in the equatorial plane we show further that it is a tennis ball pattern with an equatorial high belt and a polar low one which is clearly controlled by the rotation of the earth finally we show that the outline of pangea between at least 200 ma and 125 ma ago lay along a great circle passing through the paleo poles of rotation thus it also had an axis of symmetry in the equatorial plane this hemispheric super continent configuration ended in middle cretaceous time during a major geologic catastrophe which was accompanied by high rates of spreading hotspot outbreaks and high sea level stands we interpret this evidence in terms of separate steady state lower mantle convection responsible for the present geoid weakly coupled to the upper mantle one this weak coupling leads to the hemispheric continent configuration which ends when excessive heating of the upper mantle due to the insulating continental cap leads to continent dispersal the complete cycle from one supercontinent to the next might be of the order of 400 ma

ocean response to wind variations warm water volume and simple models of enso in the low frequency approximation abstract physical processes that control enso are relatively fast for instance it takes only several months for a kelvin wave to cross the pacific basin tk 2 months while rossby waves travel the same distance in about half a year compared to such short time scales the typical periodicity of el nino is much longer t 2 7 yr thus enso is fundamentally a low frequency phenomenon in the context of these faster processes here the author takes advantage of this fact and uses the smallness of the ratio ek tk t to expand solutions of the ocean shallow water equations into power series the actual parameter of expansion also includes the oceanic damping rate using such an expansion referred to here as the low frequency approximation the author relates thermocline depth anomalies to temperature variations in the eastern equatorial pacific via an explicit integral operator this allows a simplified formulation of enso dynamics based on an integro differential equation within this formulation

collective role of thermocline and zonal advective feedbacks in the enso mode the vertical advection of anomalous subsurface temperature by the mean upwelling and the zonal advection of mean sea surface temperature sst by anomalous current are known to be essential for the equatorial sst anomaly associated with the el nino southern oscillation enso in the coupled model these two processes are referred to as the thermocline feedback and the zonal advective feedback respectively using a version of a recharge oscillator model for enso obtained from the stripped down approximation of the cane zebiak type model it is demonstrated that these two feedbacks which are linked dynamically through the geostrophic approximation tend constructively to contribute to the growth and phase transition of enso however these two feedbacks control the leading coupled mode in different ways the thermocline feedback leads to a coupled mode through the merging of the damped sst mode and ocean adjustment mode whereas the zonal advective feedback tends to destabilize the gravest ocean basin mode with both of these feedbacks the leading modes of the coupled model still can be traced back to these different origins under moderate changes in the model setup the main consequence of these sensitivities is that the growth rate and frequency of the enso mode may be sensitive to slight changes in basic state parameters which control the strength of these feedbacks