the evolution of early oceanic lithosphere in the southern red sea abstract it seems generally agreed that the red sea has formed by the rotation of arabia from africa about a pole of rotation at 36 5 n 18 0 e but the exact way in which the oceanic lithosphere has evolved between the separating plates remains unclear this paper is concerned with the evolution of the earliest oceanic lithosphere in the southern red sea a combined study is made of gravity magnetic and seismic refraction data for a region on the southeast margin of the red sea between 16 3 n 17 3 n and 41 6 e 43 1 e a model is evolved which satisfies all the geological and geophysical data a feature of this model is that the ocean continent boundary might be 35 km inland from the coast and only 8 km from the exposed precambrian shield in this region the coastal plain being underlain by early oceanic lithosphere this implies that the break in the continental lithosphere was fairly clean

sea ice motion in response to geostrophic winds it is an old rule of thumb that sea ice moves with a speed of about 2 of the surface wind and about 45 to the right of the wind a similar relationship between the ice velocity and the geostrophic wind is examined here it is found that only about half of the long term several month average ice motion is directly related to the geostrophic wind the other half being due to the mean ocean circulation on shorter time scales and in all seasons more than 70 of the variance of the ice velocity in the central arctic ocean is explained by the geostrophic wind within about 400 km of the coasts the geostrophic wind is less successful in explaining the ice motion the spatial variations in ice velocity are also partly explained by the geostrophic wind about half of the variance in the large scale ice vorticity and shear are accounted for on the other hand none of the large scale ice divergence can be explained by the wind the long term average ocean current is estimated by subtracting the share of the ice motion caused by the wind from the total ice motion

tracking the arctic s shrinking ice cover another extreme september minimum in 2004 1 satellite passive microwave observations document an overall downward trend in arctic sea ice extent and area since 1978 while the record minimum observed in september 2002 strongly reinforced this downward trend extreme ice minima were again observed in 2003 and 2004 although having three extreme minimum years in a row is unprecedented in the satellite record attributing these recent trends and extremes to greenhouse gas loading must be tempered by recognition that the sea ice cover is variable from year to year in response to wind temperature and oceanic forcings

upwelling in the alaskan beaufort sea atmospheric forcing and local versus non local response abstract the spin up and relaxation of an autumn upwelling event on the beaufort slope is investigated using a combination of oceanic and atmospheric data and numerical models the event occurred in november 2002 and was driven by an aleutian low storm the wind field was strongly influenced by the pack ice distribution resulting in enhanced winds over the open water of the chukchi sea flow distortion due to the brooks mountain range was also evident mooring observations east of barrow canyon show that the beaufort shelfbreak jet reversed to the west under strong easterly winds followed by upwelling of atlantic water onto the shelf after the winds subsided a deep eastward jet of atlantic water developed centered at 250 m depth an idealized numerical model reproduces these results and suggests that the oceanic response to the local winds is modulated by a propagating signal from the western edge of the storm the disparity in wave speeds between the sea surface height signal traveling at the fast barotropic shelf wave speed versus the interior density signal traveling at the slow baroclinic wave speed leads to the deep eastward jet the broad scale response to the storm over the chukchi sea is investigated using a regional numerical model the strong gradient in windspeed at the ice edge results in convergence of the offshore ekman transport leading to the establishment of an anti cyclonic gyre in the northern chukchi sea accordingly the chukchi shelfbreak jet accelerates to the east into the wind during the storm and no upwelling occurs west of barrow canyon hence the storm response is fundamentally different on the beaufort slope upwelling versus the chukchi slope no upwelling the regional numerical model results are supported by additional mooring data in the chukchi sea

alaska landfast sea ice links with bathymetry and atmospheric circulation 1 using radarsat synthetic aperture radar sar imagery of northern alaska and northwestern canada we calculated a mean climatology of the annual landfast ice cycle for the period 1996 2004 we also present the monthly minimum mean and maximum landfast ice extents throughout the study area these data reveal where and when the landfast is most stable and which sections of the coast are susceptible to midseason breakout events stabilization of landfast ice is strongly related to the advance of the seaward landfast ice edge slie into waters around 18 m deep isobaths near this depth are a good approximation for midseason landfast ice extent comparison with work from the 1970s suggests a reduced presence of landfast ice in this region of the arctic due to later formation and earlier breakup this will likely lead to an increase in coastal erosion and may also have profound effects upon subsistence activities which are intimately linked to the timing of marine mammal migration patterns interannually landfast ice formation correlates with the incursion of pack ice into coastal waters suggesting that the later mean date of formation in recent years may be related to the increasingly northward location of the perennial sea ice edge the timing of breakup correlates well with onset of thawing air temperatures analysis of regional data shows a multidecadal trend toward earlier thaw onset which suggests that the observed change in breakup dates may be part of a longer term trend

a modeling study of coastal circulation and landfast ice in the nearshore beaufort and chukchi seas using ciom this study investigates sea ice and ocean circulation using a 3 d 3 8 km ciom coupled ice ocean model under daily atmospheric forcing for the period 1990 2008 the ciom was validated using both in situ observations and satellite measurements the ciom successfully reproduces some observed dynamical processes in the region including the bering inflow originated coastal current that splits into three branches alaska coastal water acw central channel branch and herald valley branch in addition the beaufort slope current bsc the beaufort gyre the east siberian current esc mesoscale eddies and seasonal landfast ice are well simulated the ciom also reproduces reasonable interannual variability in sea ice such as landfast ice and anomalous open water less sea ice during the positive dipole anomaly da years vice versa during the negative da years sensitivity experiments were conducted with regard to the impacts of the bering strait inflow heat transport onshore wind stress and sea ice advection on sea ice change in particular on the landfast ice it is found that coastal landfast ice is controlled by the following processes wind forcing bering strait inflow and sea ice dynamics

pangaean divergent margins historical perspective abstract pangaean divergent margins caused by the breakup by rifting of that supercontinent display three distinct evolutionary stages in their youth or rift stage divergent margins display a synsediment fault style that has considerable tectonic instability during the mature or drift stage seafloor spreading continental margins are relatively stable and are dominated by thermal subsidence these two stages rifting and drifting are separated in many areas by an unconformity coeval with the oldest associated oceanic crust the breakup unconformity in some areas the onset of seafloor spreading is marked by intense magmatic activity sediment facies the rifting stage range from continental clastics landward of the continental basement hinge and along the flanks of the basin to saline deposits and more open water carbonates in the axial zone of the rift lithologies emplaced during the rift or mature stage of margin development range from shallow clastics carbonates to deep water carbonate siliceous oozes turbidites and contourites some of which were deposited in an anoxic environment deposition then is controlled by changes in configuration of basins changes in sea level and plate migration through several climatic belts during the final or old age of margin development divergence gives way to convergence this stage which generally terminates with continental collision is characterized by tectonism magmatic activity and crustal shortening mesozoic divergent margins along the east west trending former tethys ocean have reached this stage in their evolution

polynya flux model solutions incorporating a parameterization for the collection thickness of consolidated new ice previous polynya flux models have specified a constant value for the collection thickness of frazil ice h at the polynya edge in certain circumstances this approach can cause the frazil ice depth h within the polynya to exceed h a result which violates assumptions made in the formulation of the ice flux balance equations at the polynya edge to overcome this problem a parameterization for h is derived in terms of the depth of frazil ice arriving at the polynya edge and the component normal to the polynya edge of the frazil ice velocity relative to the velocity of the consolidated ice pack thus h is coupled to the unknown polynya edge using the new parameterization for h an analysis of the unsteady one dimensional opening of a coastal polynya is presented analytical solutions are also derived using the new parameterization for h for steady state two dimensional polynyas adjacent to a semi infinite and finite length coastal barrier the latter case representing a prototype island in all cases the solutions show close qualitative and quantitative agreement with those derived using a constant value for h however the steady state two dimensional polynya edge can in certain circumstances exhibit a corner at the point where the offshore equilibrium width is reached precise conditions for the existence of a corner are derived in terms of the orientation of the frazil ice velocity u and the consolidated ice velocity u upper and lower bounds are also obtained for the area of the steady state island polynya and it is shown that over a large range of orientations of u and u the area exceeds that associated with the island polynya with constant h finally two simulations of the st lawrence island polynya are presented using the new parameterization for h and the results are compared with the h constant theory

seismic gravity and magnetic surveys in the central part of the red sea their interpretation and implications for the structure and evolution of the red sea abstract while there is unanimous agreement that the axial part of the red sea has witnessed seafloor spreading since the early pliocene opinions diverge considerably with regard to the situation in the main trough and shelves new high precision data comprising palaeomagnetic seismic gravity magnetic and bathymetric measurements from the central and northern parts of the red sea have been examined to discriminate between the earlier proposed hypotheses and to formulate an evolutionary model for the red sea the results show that oceanic crust extends for about 80 km at 19 n on each side of the spreading axis symmetrical seafloor spreading magnetic anomalies are recognized out to anomaly 3a 6 m y b p between 18 30 and 19 45 n anomaly 2a between 19 45 and 20 n and near 21 n anomaly 2 near 22 n and only anomaly 1 near 23 30 n although anomaly 3a is the oldest recognizable magnetic anomaly the extent and configuration of the oceanic basement as determined from seismic measurements indicate that spreading has started and continued without a hiatus since 10 12 m y b p prior to the initiation of oceanic accretion an extension of 40 55 km i e 50 70 has taken place in the proterozoic continental lithosphere whereas a separation of 70 160 km has occurred during the seafloor spreading phase several lines of evidence indicate that the shelves and the marginal parts of the main trough are of continental nature

long term ice variability in arctic marginal seas abstract examination of records of fast ice thickness 1936 2000 and ice extent 1900 2000 in the kara laptev east siberian and chukchi seas provide evidence that long term ice thickness and extent trends are small and generally not statistically significant while trends for shorter records are not indicative of the long term tendencies due to large amplitude low frequency variability the ice variability in these seas is dominated by a multidecadal low frequency oscillation lfo and to a lesser degree by higher frequency decadal fluctuations the lfo signal decays eastward from the kara sea where it is strongest in the chukchi sea ice variability is dominated by decadal fluctuations and there is no evidence of the lfo this spatial pattern is consistent with the air temperature north atlantic oscillation nao index correlation pattern with maximum correlation in the near atlantic region which decays toward the north pacific sensitivity analysis shows that dynamical forcing wind or surfac

the timing of uplift volcanism and rifting peripheral to the red sea a case for passive rifting prior to the formation of the red sea the northeastern afro arabian continent had low relief and was largely below sea level from the late cretaceous to the early oligocene the events leading to the formation of the red sea followed the sequence 1 alkaline volcanism and rifting beginning about 30 32 ma affecting a narrow linear zone in the continent 2 rotational block faulting and detachment faulting well underway by 25 ma 3 gabbro and diorite magmatism andesite to rhyolite volcanism and fine grained nonmarine sedimentation in the rift between 20 and 25 ma 4 fine grained marine sedimentation in the rift as the early shelves started to subside in the middle miocene and 5 uplift of the adjacent continents about 3 km and subsidence of the shelves about 4 km between 13 8 and 5 ma the youth of the uplift is suggested by 44 fission track dates on apatites from rocks of the proterozoic arabian shield that range in age from 13 8 to 568 ma the youngest of these ages coupled with the present high relief along the arabian escarpment and published heat flow measurements indicate that 2 5 4 km uplift has occurred in the last 13 8 m y the sequence volcanism rifting followed by uplift leads to our adoption of a passive mantle model for rift origin models that require uplift to create the rift are rejected because of the late uplift we advocate a model of lithospheric extension caused by two dimensional plate stress over those requiring tractional drag at the base of the lithosphere caused by vigorous flow in the asthenosphere it is acknowledged that traction models could explain the observed data but they imply a rigid static lithosphere and seem to require a link between the direction of flow in the asthenosphere and plate motions neither requirement is necessary in the extension model the rift starts with mechanical extension in a narrow zone of lithosphere between 25 32 ma in our model the thinned lithosphere is replaced by upwelling asthenosphere and by rocks from the adjacent deep continental lithosphere which flow into the rift ductile flow of the deep continental lithosphere is accelerated by partial melting as rocks flow upward toward the rift axis once partially melted rocks formerly part of the continental lithosphere join the upwelling asthenosphere resulting in a rapid erosion of the lithospheric mantle beneath the continent near the rift edge the resulting density decrease explains the uplift we think that the red sea began as a consequence of changing plate geometries resulting from the collision of india and eurasia after the collision the segment of the owens fracture zone north of the carlsberg ridge became locked forcing the northeast corner of afro arabia to rotate with the indian plate away from the rest of africa

seasonal and interannual variability of fast ice extent in the southeastern laptev sea between 1999 and 2013 along with changes in sea ice extent thickness and drift speed arctic sea ice regime is characterized by a decrease of fast ice season and reduction of fast ice extent the most extensive fast ice cover in the arctic develops in the southeastern laptev sea using weekly operational sea ice charts produced by arctic and antarctic research institute aari russia from 1999 to 2013 we identified five main key events that characterize the annual evolution of fast ice in the southeastern laptev sea linking the occurrence of the key events with the atmospheric forcing bathymetry freezeup and melt onset we examined the processes driving annual fast ice cycle the analysis revealed that fast ice in the region is sensitive to thermodynamic processes throughout a season while the wind has a strong influence only on the first stages of fast ice development the maximal fast ice extent is closely linked to the bathymetry and local topography and is primarily defined by the location of shoals where fast ice is likely grounded the annual fast ice cycle shows significant changes over the period of investigation with tendencies toward later fast ice formation and earlier breakup these tendencies result in an overall decrease of the fast ice season by 2 8 d yr which is significantly higher than previously reported trends

seismic study of the crust of the northern red sea and gulf of suez we report the results of fifteen expanding spread profiles esp s and a seismic wide angle reflection refraction une performed during march april 1986 in the gulf of suez and the egyptian part of the northern red sea area north of 25 n four 16 4 air guns were used as a sound source on board r v le suroit and a 96 channel 2 4 km long streamer was towed by a supply vessel the whity tide most of the profiles show good crustal reflection and refraction arrivals and often good moho arrivals obtained for a distance of 80 to 100 km we present the results of x t and p analysis obtained by a velocity inversion performed in the p plane and by ray tracing modeling of both the p and the x t sections the velocity models are computed for planar and linear gradient velocity layers the northernmost part of the red sea appears to be characterized by a continental type crust extremely thinned 4 lying at a mean depth of 7 8 km whereas the moho is at a mean 14 15 km depth the southern part shows a seismic velocity structure of an oceanic type except in the 40 km closest to the coastline in both parts seismic waves progressively get more attenuated with distance from the shore to the axial zone which is presently tectonically active the difference between the northern continental and southern oceanic zone is related to the termination of the levant fault the northern continental area appears to represent the termination of the levant fault as a zone of distributed deformation

seasonal variation of upwelling in the alaskan beaufort sea impact of sea ice cover 1 data from a mooring array deployed from august 2002 to september 2004 are used to characterize differences in upwelling near the shelf break in the alaskan beaufort sea due to varying sea ice conditions the record is divided into three ice seasons open water partial ice and full ice the basic response is the same in each of the seasons roughly 8 h after the onset of easterly winds the shelf break jet reverses followed approximately 10 h later by upwelling of saltier water which is cold near the shelf break pacific winter water and warm at depth atlantic water the secondary circulation at the outer shelf is to first order consistent with a two dimensional ekman balance of offshore flow in the upper layer and onshore flow at depth there are however important seasonal differences in the upwelling overall the response is strongest in the partial ice season and weakest in the full ice season it is believed that these differences are dictated by the degree to which wind stress is transmitted through the pack ice as the strength of the wind forcing was comparable over the three seasons an eof based upwelling index is constructed using information about the primary flow secondary flow and hydrography the ability to predict upwelling using the wind record alone is explored which demonstrates that 90 of easterly wind events exceeding 9 5 m s 1 drive significant upwelling during certain periods the ice cover on the shelf became landfast which altered the upwelling and circulation patterns near the shelf break

near earth initiation of a terrestrial substorm 1 despite the characterization of the auroral substorm more than 40 years ago controversy still surrounds the processes triggering substorm onset initiation that stretching of the earth s magnetotail following the addition of new nightside magnetic flux from dayside reconnection powers the substorm is well understood the trigger for explosive energy release at substorm expansion phase onset is not using ground based data sets with unprecedented combined spatial and temporal coverage we report the discovery of new localized and contemporaneous magnetic wave and small azimuthal scale auroral signature of substorm onset these local auroral arc undulations and magnetic field signatures rapidly evolve on second time scales for several minutes in advance of the release of the auroral surge we also present evidence from a conjugate geosynchronous satellite of the concurrent magnetic onset in space as the onset of magnetic pulsations in the ionosphere to within technique error throughout this time period the more poleward arcs that correspond to the auroral oval which maps to the central plasma sheet remain undisturbed there is good evidence that flows from the midtail crossing the plasma sheet can generate north south auroral structures yet no such auroral forms are seen in this event our observations present a severe challenge to the standard hypothesis that magnetic reconnection in stretched magnetotail fields triggers onset indicating substorm expansion phase initiation occurs on field lines that are close to the earth as bounded by observations at geosynchronous orbit and in the conjugate ionosphere

a new technique for determining substorm onsets and phases from indices of the electrojet sophie we present a new quantitative technique that determines the times and durations of substorm expansion and recovery phases and possible growth phases based on percentiles of the rate of change of auroral electrojet indices by being able to prescribe different percentile values we can determine the onset and duration of substorm phases for smaller or larger variations of the auroral index or indeed any auroral zone ground based magnetometer data we apply this technique to the supermag al sml index and compare our expansion phase onset times with previous lists of substorm onsets we find that more than 50 of events in previous lists occur within 20 min of our identified onsets we also present a comparison of superposed epoch analyses of sml based on our onsets identified by our technique and existing onset lists and find that the general characteristics of the substorm bay are comparable by prescribing user defined thresholds this automated quantitative technique represents an improvement over any visual identification of substorm onsets or indeed any fixed threshold method

crustal and uppermost mantle structure beneath the afro arabian rift system abstract this contribution presents data and results from long range seismic refraction wide angle reflection lines in the afro arabian rift system from the derived crustal structure an evolutionary model is proposed in terms of the amount of crustal thinning in this model the gulf of aden and the axial trough of the southern red sea where the continental crust was thinned so much as to allow thin oceanic crust to form are representative of one end of the spectrum progressing through the northern part of the red sea main trough on the egyptian side with a crustal thickness of 11 14 km to the northern and southern parts of the red sea main trough on the arabian side and the northern afar depression with 15 20 km thick crusts followed by the southern afar depression with a crustal thickness of 22 26 km the members of the other end of the spectrum are reached these include the jordan dead sea and east african rifts which each with a crustal thickness of 30 36 km represent the least thinned closest to normal thickness continental crust in determining the amount and nature of opening of the red sea there remain however many problems argely due to the non unique correspondence of seismic velocity to rock type this may lead to uncertainty in moho depths especially in areas close to the mid ocean ridge system e g the southeastern part of the afar depression in the region around the gulf of tadjura where velocities as low as 6 8 6 9 km s have been interpreted as representirg hot anomalous mantle it also causes uncertainty as to what percentage of the present crust is stretched and thinned original continental crust and what percentage is new crust whether it be truly oceanic or basic intrusiors into continental crust thus it is felt that there is still an urgent need for geoscientific experiments in the afro arabian rift to resolve the details of continental rifting and subsequent oceanic crust emplacement

tectonic evolution of the northwestern red sea margin as related to basement structure abstract at the northwestern egyptian margin of the red sea a crystalline basement of pan african late proterozoic age is exposed beneath a phanerozoic sedimentary cover this tectonic situation provided an opportunity to study the younger red sea tectonic evolution in relation to features that are inherited from or reactivated in an underlying basement two structural maps compiled from published sources and our data covering the eastern egyptian basement from hurghada to the south show the most important structural elements the major central and southern parts of the basement in eastern egypt ced and sed are dominated by low angle thrusts other fractures n s e w nw se are distinctly less frequent and of local importance nw se oriented strike slip faults najd system overprinted the low angle thrusts of the northern ced these fault are related to ne sw trending normal faults which characterize the northern part of the basement ned before discussing general relationships between basement structure and red sea evolution a detailed example of the post pan african phanerozoic evolution of the low angle thrust dominated domains of the ced and the sed from a traverse south of 25 n is presented there detailed structural mapping showed phanerozoic normal faults close to the red sea trending nnw sse and at the margin of the phanerozoic cover east of the nile trending nnw sse and nw se leading to a horst like position of the basement within this horst deformation is restricted to a local sinistral strike slip fault trending n s the normal faults frequently used and reactivated fractures parallel or normal to the axial surface of earlier pan african folds igneous activity is confined to the western part of the basement where mafic dykes mafic to trachytic volcanics the alkaline gabal abu khrug ring complex and trachyte plugs in that time sequence from 104 to 80 ma are exposed mafic dykes are dependent on host rock properties distributed mainly in relatively brittle granitoid rocks trachyte intrusions are generally not related to particular host rocks but may follow pre existing structures crosscutting relationships with the igneous rocks imply a late cretaceous age for the faults in the west of the traverse however in the east at the red sea coast faults cut middle miocene sediments and are thus younger tectonic activity in the traverse area is therefore confined to two distinct episodes a late cretaceous event of alkaline magmatism and normal faulting at the western margin of the basement and a miocene or younger event of normal faulting at the present red sea coast in contrast to earlier views neither transform faults nor large scale riedel shears related to red sea tectonics have been met in the area this holds also true for the ced and sed as a whole where only local faults remain for potential reactivation during red sea tectonics except perhaps the duwi shear zone at quseir the prevailing n s e w or nw se directions of these faults preclude an interpretation as possible transform faults normal to the spreading axis of the red sea therefore it is no longer possible to assume a continuation of red sea transform faults into the continental crust

the afro arabian rift system an overview abstract the afro arabian rift system is reviewed beginning with the dead sea transform and gulf of suez in the north followed by the gulf of aden and red sea and ending with a brief mention of rifting through eastern and southern africa a consistent interpretation is obtained for geophysical data from the gulf of aden and red sea and geological data for the dead sea transform suez graben and red sea and gulf of aden margins geophysical data are used to estimate the locations of the ocean continent boundaries in the northern red sea these are found to coincide when the total 107 km shear along the dead sea is restored the red sea is therefore reconstructed in stages beginning with the 45 km post miocene shear and 62 km early miocene shear along the dead sea transform followed by estimates for extension in the early red sea suez graben when this is done there is a remarkable alignment of various features revealed on landsat tm imagery for both sides of the northern red sea north south differences in the red sea and west east differences hi the gulf of aden are discussed and found to be best explained by a propagating rift model

automated determination of auroral breakup during the substorm expansion phase using all sky imager data this paper describes a novel method for quantitatively and routinely identifying auroral breakup following substorm onset using the time history of events and macroscale interactions during substorms all sky imagers substorm onset is characterized by a brightening of the aurora that is followed by auroral poleward expansion and auroral breakup this breakup can be identified by a sharp increase in the auroral intensity i t and the time derivative of auroral intensity i t utilizing both i t and i t we have developed an algorithm for identifying the time interval and spatial location of auroral breakup during the substorm expansion phase based solely on quantifiable characteristics of the optical auroral emissions we compare the time interval determined by the algorithm to independently identified auroral onset times from three previously published studies in each case the time interval determined by the algorithm is within error of the onset independently identified by the prior studies we further show the utility of the algorithm by comparing the breakup intervals determined using the automated algorithm to an independent list of substorm onset times we demonstrate that 50 of the breakup intervals characterized by the algorithm are within the uncertainty of the times identified in the list the quantitative description and routine identification of an interval of auroral brightening during the substorm expansion phase provides a foundation for unbiased statistical analysis of the aurora and to probe the physics of the auroral substorm and identify the processes leading to auroral substorm onset

new constraints on red sea rifting from correlations of arabian and nubian neoproterozoic outcrops new constraints on the mechanics of red sea opening were obtained by correlating neoproterozoic outcrops of the arabian and nubian shields along two thirds of the red sea coastlines using a mosaic of 23 landsat thematic mapper scenes 5 105 km together with field geochemical and geochronological data we identified and mapped lithologic units mobile belts and terranes within the arabian and nubian shields features best align if arabia is rotated by 6 7 around a pole at latitude 34 6 n longitude 18 1 e implications of our reconstruction include 1 the amount of continental crust underlying the red sea is small because the restored red sea coasts are typically juxtaposed 2 only a single pole is needed implying that the arabian and nubian shields were rigid plates during red sea rifting 3 coastlines reorient to align with preexisting structures suggesting the rift propagated in part along pre existing zones of weakness 4 large sinistral displacements of up to 350 km along the red sea are not supported 5 the pole is inconsistent with the pliocene pleistocene motion along the dead sea transform pole 32 8 n 22 6 e 0 5 joffe and garfunkel 1987 indicating that more than one phase of motion is required to account for the red sea opening however our pole is similar to that for the total motion along the dead sea transform pole 32 7 n 19 8 e 2 joffe and garfunkel 1987 suggesting that the motion between arabia and nubia was parallel to the total motion along the dead sea transform

variability of sea ice in the northern weddell sea during the 20th century the record of winter fast ice in the south orkney islands northern weddell sea antarctica is over a century long and provides the longest observational record of sea ice variability in the southern hemisphere here we present analyses of the series of fast ice formation and breakout dates from 1903 to 2008 we show that over the satellite era post 1979 the timing of both final autumn formation and complete spring breakout of fast ice is representative of the regional sea ice concentrations sic in the northern weddell sea and associated with atmospheric conditions in the amundsen sea region to the west of the antarctic peninsula variation in the fast ice breakout date is influenced by the intensity of the westerly north westerly winds associated with the southern annular mode sam in contrast the date of ice formation displays correlations with regional oceanic and sea ice conditions over the previous 18 months which indicate a preconditioning during the previous summer and winter and exhibits variability associated with variation in tropical pacific sea surface temperature i e the el nino sothern oscillation enso a reduction in fast ice duration at the south orkney islands around the 1950s was associated with both later formation and earlier breakout however there were marked changes in variability with periodicities of 3 5 year 7 9 year and 20 year in each of the series and in their relationships with enso and sam indicating the need for caution in interpreting changes in ice conditions based on shorter term satellite series

magnetic evidence for the nature of the crust beneath the southern red sea magnetic data over the southern red sea are used to examine various models for the evolution of the region the linear nature of the magnetic anomalies over the coastal margins and adjacent portions of the main trough together with their decrease in amplitude with elevation is shown to be compatible with deep thin sources that are strongly magnetized the general lack of correspondence between gravity anomalies and deskewed magnetic anomalies indicates that the anomalies are due to intrabasement bodies rather than basement relief associated with density contrasts across axis correlations of individual anomalies indicate a symmetrical disposition of magnetic sources about a line close to the present deep water axis the regular symmetrical pattern of linear anomalies strongly suggests a seafloor spreading origin the combined geologic and geophysical evidence therefore supports a model in which the margins are underlain by material more typically oceanic in character than continental the magnetic evidence further implies that this oceanic crust formed during an earlier phase of spreading in the red sea although the age of this crust is unknown anomaly correlations suggest spreading may have taken place during the late oligocene early miocene

the 23 january 2014 jizan earthquake and its tectonic implications in southwestern saudi arabia abstract a moderate sized earthquake of mw 4 4 occurred in southwestern saudi arabia on 23 january 2014 the event is considered as the largest observed earthquake that has occurred in the epicentral area to examine the seismogenic stress regime and resolve the fault plane ambiguity the hypocenter locations and focal mechanisms were determined using well recorded waveforms of the broadband stations operated by the saudi geological survey the current analysis included dataset consisting of mainshock and a total number of 113 well located aftershocks focal mechanism solutions of the mainshock and fifteen aftershocks were determined the focal mechanism solutions were inverted using stress tensor inversion it indicates that the maximum compressive stress 1 has a nearly shallow plunge 11 8 of ese orientation and minimum compressive stress 3 has a shallow plunge 0 3 toward nne our results obtained from precise earthquake locations focal mechanism solutions and stress tensor inversion reveal dextral strike slip faulting over the ene wsw striking plane the analysis of coulomb failure stress emphasized the causative fault of the 2014 jizan earthquake sequence the active fault implies a reactivation of a high angle fault buried in the precambrian basement which is conjugate to the red sea spreading axis and nnw sse najd fault system the present study provided an impetus toward understanding the seismogenic stress regime in a virgin area

tectonic development of passive continental margins of the southern and central red sea with a comparison to wilkes land antarctica abstract the continental margins of the southern and central red sea and most of wilkes land antarctica have bulk crustal configurations and detailed structures that are best explained by a prolonged history of magmatic expansion that followed a brief but intense period of mechanical extension extension on the red sea margins was spatially confined to a rift that was 20 30 km in width the rifting phase along the arabian margin of the central and southern red sea occurred 25 32 ma ago primarily by detachment faulting at upper crustal levels and ductile uniform stretching at depth rifting was followed by an early magmatic phase during which the margin was invaded by dikes and plutons primarily of gabbro and diorite at 20 24 ma after the crust was mechanically thinned from 40 km to 20 km we infer continued spreading after that in which broad shelves were formed by a process of magmatic expansion because the offshore crust is only 8 15 km thick including sediment and seismic reflection data do not depict horst and graben or half graben structures from which mechanical extension might be inferred the wilkes land margin is similar to the arabian example the margin is about 150 km in width the amount of upper crustal extension is too low to explain the change in sub sediment crustal thickness from 35 km on the mainland to

structure of the red sea at 20 n from gravity data and its implication for continental margins structure of the red sea at 20 n from gravity data and its implication for continental margins

sea ice thickness variability in the chukchi sea spring and summer 2002 2004 abstract measurements of sea ice thickness were obtained from drill holes an ice based electromagnetic induction instrument iem and a ship borne electromagnetic induction instrument sem during the early melt season in the southern chukchi sea in 2002 and 2004 and in late summer 2003 at the time of minimum ice extent in the northern chukchi sea an ice roughness criterion was applied to distinguish between level and rough or ridged ice ice thickness modes in the probability density functions pdfs derived from drill hole and iem measurements agreed well with modes at 1 5 1 6 and 1 8 1 9 m for all data from level ice the pdfs derived from sem measurements show that the primary modes are at 0 1 and 1 1 m in 2003 and 0 7 m in 2004 in 2002 and 2004 significant fractions between one third and one half of level ice were found to consist of rafted ice segments snow depth varied significantly between years with 2004 data showing more than half the snow cover on level ice to be at or below 0 05 m depth in late spring ice growth simulations and examination of ice drift and deformation history indicate that impacts of atmospheric and oceanic warming on level ice thickness in the region over the past few decades are masked to a large extent by variability in snow depth and the contribution of deformation processes in comparison with submarine sonar ice thickness data from previous decades a reduction in ice thickness by about 0 5 1 m is in part explained by the replacement of multi year with first year ice over the chukchi and beaufort shelves

upwelling on the continental slope of the alaskan beaufort sea storms ice and oceanographic response 1 the characteristics of pacific born storms that cause upwelling along the beaufort sea continental slope the oceanographic response and the modulation of the response due to sea ice are investigated in fall 2002 a mooring array located near 152w measured 11 significant upwelling events that brought warm and salty atlantic water to shallow depths when comparing the storms that caused these events to other aleutian lows that did not induce upwelling interesting trends emerged upwelling occurred most frequently when storms were located in a region near the eastern end of the aleutian island arc and alaskan peninsula not only were these storms deep but they generally had northward tending trajectories while the steering flow aloft aided this northward progression the occurrence of lee cyclogenesis due to the orography of alaska seems to play a role as well in expanding the meridional influence of the storms in late fall and early winter both the intensity and frequency of the upwelling diminished significantly at the array site it is argued that the reduction in amplitude was due to the onset of heavy pack ice while the decreased frequency was due to two different upper level atmospheric blocking patterns inhibiting the far field influence of the storms

a record minimum arctic sea ice extent and area in 2002 1 arctic sea ice extent and area in september 2002 reached their lowest levels recorded since 1978 these conditions likely resulted from 1 anomalous warm southerly winds in spring advecting ice poleward from the siberian coast 2 persistent low pressure and high temperatures over the arctic ocean in summer promoting ice divergence and rapid melt

magmatism of the eastern red sea margin in the northern part of yemen from oligocene to present the northern part of yemen during the last 30 ma has been the site of an intense magmatic activity which can be divided into three main episodes the first episode lasted from 30 to 18 ma and was characterized by two climaxes huge flood basalt eruptions between 30 to 26 ma were succeeded by massive ignimbrite sheet deposits and intrusion of silicic subvolcanic masses 22 to 20 ma ago contemporaneously along the present day western margin of the yemen plateau a basaltic dike swarm was emplaced additionally alkaline and peralkaline granites were intruded at the end of the first climax and throughout the second after a long quiescence magmatic activity occurred again in late miocene time about 10 ma with extrusion of lava flows in scattered areas e g al harf wadi as sirr maswar al hada jabal an nar the third magmatic episode has been concentrated in three well defined areas it began about 6 5 ma ago in the dhamar rada area and later in the san a amram and sirwah marib areas new chemical and isotopic data on the magmatic products of north yemen indicate that extensive crustal contamination together with simple crystal fractionation processes have been operating during the magmatic evolution the most primitive products of each of the three episodes share isotopic and petrological features suggesting a similar mantle source isotope geochemistry indicates an important asthenospheric component in the mantle source for the magmas of all three episodes finally a comparison between the coeval igneous rocks of the yemen and ethiopia plateaus is attempted

the red sea gulf of aden re assessment of hydrocarbon potential abstract the results and conclusions of the undp world bank red sea gulf of aden regional hydrocarbons study project june 1989 january 1992 are summarized these derive from detailed examination of pooled public sector data provided to the project by the participating bordering states in the region these included samples and logs from about 56 wells drilled in the two basins out of a total of 71 and about 30 000 line km of reflection seismic data selected from 110 000 km available well logs were digitized and correlated and basinwide biostratigraphic lithostratigraphic and palaeoenvironmental studies source rock organic richness quality and maturity studies and sedimentological analyses studies were performed by contracted specialist staff in the uk and france these were integrated with basinwide seismic structural and isopach mapping for selected regional reflectors intervals by national task forces in cairo under project supervision academically acquired crustal seismic and other geophysical data and oil industry velocity and other borehole data were also integrated for the red sea modelling utilizing recently acquired geophysical data indicates crustal asymmetry for the red sea rift with oceanic crust of pull apart basin type flooring some portions of offshore egypt and sudan on the west and stretched continental crust underlying the eastern arabian flank these interpretations furthermore suggest that sinistral strike slip processes controlled the initial break up of the arabian plate shaping the african flank as a sharp plate boundary similar processes appear to have initially shaped the somalia flank of the gulf of aden rift only later did true seafloor spreading propagate in the eastern gulf of aden 10 12 ma about a regional lithostratigraphic nomenclature scheme for the miocene recent syn and post rift red sea successions keyed to detailed biostratigraphical distribution charts and microfaunal assemblage characteristics was erected tied to the well documented and understood petroliferous gulf of suez basin scheme this allows facies variations within the basin to be compared and allows consistent interpretation and correlations across the basin to which local informal nomenclature can be related pre rift pre oligocene marine sediments are present in most of the gulf of aden jurassic eocene but only incompletely on the basin margins in the red sea jurassic in the south upper cretaceous early palaeogene in the north significant pre rift oil gas prone upper jurassic cretaceous and palaeogene source rocks occur in gulf of aden sub basins initiated by late jurassic early cretaceous tensional tectonics with maturity levels ranging from early late to post mature whereas early synrift source rocks are generally immature in the red sea good quality pre rift source rocks outcrop in the north and south but are probably overmature for oil in the basin except in the extreme south if present good syn pre and post salt and post rift source levels occur throughout the basin but in the central southern sectors only the post salt remains within the oil window because of high geothermal gradients both basins are little explored attractive pre rift jurassic eocene exploration plays in rotated fault and horst blocks in predominantly carbonate but subordinate sandstone reservoirs are present in the gulf of aden confirmed by an important undeveloped eocene light oil discovery in offshore yemen with subordinate synrift potential where maturity is established relative continental shelf narrowness is economically limiting but wider sectors occur in the red sea the principal exploration plays are in miocene synrift pre and post salt successions rotated fault blocks occur in the pre salt but maturity for oil in the deeper levels is restricted to the northern sector these levels in the central and southern sectors are overmature except in the southernmost portion but excellent potential exists in the synrift post salt and early post rift sequences with a number of attractive play types reservoirs for synrift plays are mainly sandstones and potential is confirmed by several undeveloped gas and condensate discoveries and numerous oil seepages throughout the basin relatively wide continental shelves occur in the south and along much of the eastern flank

wavelet based ulf wave diagnosis of substorm expansion phase onset 1 using a discrete wavelet transform with a meyer wavelet basis we present a new quantitative algorithm for determining the onset time of pi1 and pi2 ulf waves in the nightside ionosphere with 20 to 40 s resolution at substorm expansion phase onset we validate the algorithm by comparing both the ulf wave onset time and location to the optical onset determined by the imager for magnetopause to aurora global exploration image far ultraviolet imager fuv instrument in each of the six events analyzed five substorm onsets and one pseudobreakup the ulf onset is observed prior to the global optical onset observed by image at a station closely conjugate to the optical onset the observed ulf onset times expand both latitudinally and longitudinally away from an epicenter of ulf wave power in the ionosphere we further discuss the utility of the algorithm for diagnosing pseudobreakups and the relationship of the ulf onset epicenter to the meridians of elements of the substorm current wedge the importance of the technique for establishing the causal sequence of events at substorm onset especially in support of the multisatellite time history of events and macroscale interactions during substorms themis mission is also described

a comparison of magnetic signatures and dmsp auroral images at substorm onset three case studies the authors explore the relationship between mid latitude and synchronous orbit magnetic signatures and the location of the auroral surge at the onset of three isolated magnetospheric substorms mid latitude data come from the air force geophysics laboratory magnetometer network synchronous orbit data form the satellites goes 2 and 3 and auroral data from defense meteorological satellite program auroral images and auroral magnetograms they find that the surge forms with its western edge approximately 1 hour west of the longitude where the major axis of the mid latitude pi 2 polarization ellipse is along magnetic north and where the d component perturbation of the magnetic bay is near zero these observations are in qualitative agreement with a current wedge consisting of a localized upward current in the west and a longitudinally distributed current in the east at synchronous orbit the longitude of the surge head appears to separate a region to the west where the magnetic field becomes more taillike from one to the east where the magnetic field becomes more dipolar

tectonic configuration of the western arabian continental margin southern red sea the young continental margin of the western arabian peninsula is uplifted 3 5 to 4 km and is well exposed rift related extensional deformation is confined to a zone 150 km wide inland of the present coastline at 17 to 18 n and its intensity increases gradually from east to west extension is negligible near the crest of the arabian escarpment but it reaches a value of 8 to 10 in the western asir a highly dissected mountainous region west of the escarpment there is an abrupt increase in extensional deformation in the foothills and pediment west of the asir about 40 km inland of the shoreline where rocks in the upper plate of a system of low angle normal faults with west dips are extended by 60 to 110 the faults were active 23 to 29 ma ago and the uplift occurred after 25 ma ago tertiary mafic dike swarms and plutons of gabbro and granophyre 20 to 23 ma old are concentrated in the foothills and pediment as well the chemistry of the dikes suggests 1 fractionation at 10 to 20 kbar 2 a rapid rise through the upper mantle and lower crust and 3 differentiation and cooling at 1 atm to 5 kbar structural relations between dikes faults and dipping beds indicate that the mechanical extension and intrusional expansion were partly coeval but that most of the extension preceded the expansion a tectonic reconstruction of pre red sea afro arabia suggests that the early rift was narrow with intense extension confined to an axial belt 20 to 40 km wide steep moho slopes probably developed during rift formation as indicated by published gravity data two published seismic interpretations and the surface geology

mapping arctic landfast ice extent using l band synthetic aperture radar interferometry in recent years methods have been developed to extract the seaward landfast ice edge from series of remote sensing images with most of them relying on incoherent change detection in optical infrared or radar amplitude imagery while such approaches provide valuable results some still lack the required level of robustness and all lack the ability to fully automate the detection and mapping of landfast ice over large areas and long time spans this paper introduces an alternative approach to mapping landfast ice extent that is based on coherent processing of interferometric l band synthetic aperture radar sar data the approach is based on a combined interpretation of interferometric phase pattern and interferometric coherence images to extract the extent and stability of landfast ice due to the low complexity of the base imagery used for landfast ice extraction significant improvements in automation and reduction of required manual interactions by operators can be achieved a performance analysis shows that l band interferometric sar insar data enable the mapping of landfast ice with high robustness and accuracy for a wide range of environmental conditions

thin and thinner sea ice mass balance measurements during sheba 1 as part of a large interdisciplinary study of the surface heat budget of the arctic ocean sheba we installed more than 135 ice thickness gauges to determine the sea ice mass balance while installing these gauges during the fall of 1997 we found that much of the multiyear ice cover was only 1 m thick considerably thinner than expected over the course of the yearlong field experiment we monitored the mass balance for a wide variety of ice types including first year ice ponded ice unponded ice multiyear ice hummocks new ridges and old ridges initial ice thicknesses for these sites ranged from 0 3 to 8 m and snow depths varied from a few centimeters to more than a meter however for all of their differences and variety these thickness gauges sites shared a common trait at every site there was a net thinning of the ice during the sheba year the thin ice found in october 1997 was even thinner in october 1998 the annual cycle of ice thickness was also similar at all sites there was a steady increase in thickness through the winter that gradually tapered off in the spring this was followed by a steep drop off in thickness during summer melt and another tapering in late summer and early fall as freeze up began maximum surface melting was in july while bottom ablation peaked in august combining results from the sites we found an average winter growth of 0 51 m and a summer melt of 1 26 m which consisted of 0 64 m of surface melt and 0 62 m of bottom melt there was a weak trend for thicker ice to have less winter growth and greater net loss for the year however ice growth was also impacted by the snow depth considerable variability was observed between sites in both accretion and ablation the total accretion during the 9 month growth season ranged from zero for thick ridged ice to more than a meter for young ice ponds tended to have a large amount of surface melting while ridges had considerable bottom ablation

reflection and transmission characteristics at the edge of shore fast sea ice the reflection and transmission of ocean waves at a sea ice boundary is reconsidered the sea ice is modelled as a continuous thin elastic plate of uniform thickness floating on water of arbitrary constant depth unlike earlier solutions matching of potentials between the free surface domain and the ice covered domain is done at all depths previous solutions were incompletely matched as the potentials in each domain were deficient in the present solution a number of the infinity of evanescent modes which were hitherto ignored are included in the solution and allow matching to be carried out by minimization of an integrated error term from surface to seafloor reflection and transmission are found to be markedly influenced by the inclusion of these modes suggesting that conclusions based on the incomplete potentials may be substantially in error

ionospheric localisation and expansion of long period pi1 pulsations at substorm onset 1 we examine the initial ionospheric localisation and expansion of pi1 pulsations associated with a substorm onset observed on 1st november 2006 with the combined carisma and themis gmag network of ground based magnetometers we demonstrate how the first ionospheric pulsation disturbance lies in the long period pi1 band the long period pi1 pulsations at substorm onset are initially localised in longitude and expands away from an epicentre in the ionosphere with 16 s timing between stations we further establish a link between the location of the downward field aligned current fac element which subsequently develops within the substorm current wedge scw and the initial location of the onset of long period pi1 pulsations the arrival of the initial long period pi1 wavepacket demonstrates the importance of global networks of ground based magnetometers for probing substorm onset the pi1 expansion proceeds westward at a rate of approximately 1 mlt hour per 20 seconds representing a very rapid expansion of the pi1 signal at the ground the resolution of the pi1 localisation and the rate of expansion suggest pi1 waves can play an important role in studies of the causal sequence of energy release in substorms

attenuation of surface waves across the arabian peninsula abstract amplitude spectra of fundamental mode rayleigh and love waves are used to determine shear wave q q models for the upper crust of the arabian peninsula the observed spectra are compared to theoretical spectra computed for earthquakes with known fault plane solutions shear wave q in the upper crust can be obtained by trial and error modeling to fit the the slope of the amplitude spectra at short periods 5 30 s if the source time function is less than about 6 s and if the depth of the earthquake is known to within about 3 km shear velocity q values obtained in this way vary from about 60 along the margin of the red sea to 100 150 in the central part of the peninsula to 65 80 in the eastern folded region these values are unusually low for a stable region and suggest that observed anelasticity there is affected by tectonic and epeirogenic activity which has occurred over the past 30 m y the shear wave q models derived from surface waves at periods of 5 30 s closely predict reported values of lg q at 1 hz shear wave q therefore appears to be independent of frequency in this region at periods between about 1 and 30 s

ice erosion of a sea floor knickpoint at the inner edge of the stamukhi zone beaufort sea alaska abstract in 1981 and 1982 detailed bathymetric and side scan sonar surveys were made of an area of the sea floor north of prudhoe bay alaska to study the changing characteristics of the seabed at the inner boundary of the stamukhi zone the coast parallel zone of grounded ice ridges that occurs in water depths between 15 and 50 m in the arctic the fathograms and sonographs resolved 10 cm features and electronic navigation gave relocations accurate to about 10 m year after year an ice boundary develops at the inner edge of the stamukhi zone where major shear and pressure deformation occur in about the same location associated with this ice boundary the bathymetry shows a pronounced break in slope the knickpoint on the shelf profile at about 20 m depth the 2 3 m high knickpoint is cut in a consolidated gravelly mud of pre holocene age a well defined gravel and cobble shoal a few meters high usually occurs at the inshore edge of the knickpoint the sonograph mosaic shows that seaward of the knickpoint ice gouges saturate the sea floor and are well defined inshore the gouges are fewer in number and are poorly defined on the records few gouges can be traced from the seaward side of the knickpoint across the shoals to the inshore side of the knickpoint studies of ice gouging rates in two seabed corridors that cross the stamukhi zone reveal the highest rates of gouging seaward of the knickpoint we believe that the knickpoint results from ice erosion at the inner boundary of the stamukhi zone intensified currents associated with this boundary winnow away fine sediments ice bulldozing and currents shape the shoals which perch atop the knickpoint the knickpoint helps to limit ice forces on the seabed inshore of the stamukhi zone

intensification of preexisting auroral arc at substorm expansion phase onset wave like disruption during the first tens of seconds 1 with the deployment of the all sky imager array of the themis mission we were able to construct a preliminary database of auroral substorm expansion phase onsets from which we have established a number of common features characterizing the first tens of seconds of the substorm auroral intensification we find that the intensification occurs within 10 sec over an arc segment extending approximately 1 h mlt and featuring wave like formations distributed in longitude the longitudinal wave number ranges between 100 and 300 such that the wavelength is comparable to the ion gyroradius in the central plasma sheet the scale the intensification is about 10 30 sec this study casts important observational constraints on substorm onset theories

intermittent structural weakening and acceleration of the thwaites glacier tongue between 2000 and 2018 evolving conditions at the terminus of thwaites glacier will be important in determining the rate of its future sea level contribution over the coming decades here we use remote sensing observations to investigate recent changes 2000 2018 in the structure and velocity of thwaites glacier and its floating tongue we show that the main trunk of thwaites glacier has accelerated by 38 over this period while its previously intact floating tongue has transitioned to a weaker melange of fractured icebergs bounded by sea ice however the rate of structural weakening and acceleration was not uniform across the observational period and we identify two periods of rapid acceleration and structural weakening 2006 2012 2016 2018 separated by a period of deceleration and re advance of the structurally intact shear margin boundary 2012 2015 the timing of these accelerations decelerations strongly suggests a link to variable ocean forcing the weakened tongue now has some dependency on landfast sea ice for structural integrity and is vulnerable to changes in landfast ice persistency future reductions in landfast sea ice could manifest from changes in climate and or the imminent removal of the b 22a iceberg from the thwaites embayment such changes could have important implications for the integrity of the ice tongue and future glacier discharge

miocene magmatism of sinai related to the opening of the red sea extension associated with the initial early miocene stages of opening of the red sea resulted in intrusion of a widespread system of dikes and smaller bodies primarily along the northeastern margin of the red sea gulf of suez axis dikes some up to more than 800 km in length were emplaced dominantly parallel to the red sea gulf of suez from the sinai peninsula to yemen intrusive rocks are mainly basaltic in composition but minor granophyres are also present in the sinai this magmatic event is about 20 m y old dikes of the southern and southeastern sinai crop out in precambrian terrane in the central and northern sinai they occur in phanerozoic terrane where they may be associated with linear grabens and cryptovolcanic features basaltic dikes of the sinai underwent variable degrees of alteration alteration phases include seriate quartz smectite chlorite and serpentine x ray diffraction and petrographic analysis indicate that in spite of extensive alteration primary minerals still control the major element compositions of the rocks basalts are tholeiitic in composition with sio2 48 5 to 50 and na2o k2o 3 to 3 5 rb and sr concentrations are probably dominated by alteration and by introduction of secondary material primarily carbonate zr tio2 which is relatively unchanged during alteration substantiates that the basaltic rocks are subalkaline initial 87sr 86sr determined after leaching of samples is approximately 0 7043 0 7063 much higher than red sea axial trough basalts 0 703 we infer that these sinai basalts equilibrated at depths of 35 50 km possibly within an enriched mantle whether the main trough of the red sea is underlain by extended and modified continental crust or by oceanic crust is controversial since miocene dikes were intruded along both coasts but primarily the saudi arabian coast of the red sea gulf of suez axis in a zone up to 150 km wide they may also underlie the main trough of the red sea and result at least partially in the discontinuous magnetic and gravity anomalies observed there possibly the abundance of dikes beneath the main trough is much greater than adjacent to the red sea giving rise to properties intermediate between those of continental and oceanic crust downwarping and widespread intrusion of dikes along the red sea 18 26 m y ago probably signified crustal dilation and the initiation of a continental rift because tholeiitic basalts of the sinai are higher in 87sr 86sr than red sea axial trough basalts we infer that the conditions of their origin must also be very different we suggest that the sinai basalts may have been generated within but near the base of subcrustal continental lithosphere perhaps indicating thermal thinning of lithospheric mantle above upwelled asthenosphere associated with continental rifting this inference if correct would indicate that the lithosphere was at least 35 50 km thick during the early miocene phase of rifting but possibly not much thicker since dikes farthest from the red sea are apparently identical in composition to those closest asthenospheric upwarping must have been broad enough that all magmas were derived from approximately the same depth in the yemen ethiopia areas volcanism began earlier about 30 m y ago and was much more voluminous than elsewhere along the red sea gulf of suez axis suggesting the presence of underlying mantle upwelling accompanying rifting of the red sea in spite of differences in age and volume the presence of large volumes of tholeiites among the miocene basalts of the yemen ethiopia areas suggests that the lithosphere was similarly thinned along the entire length of the red sea

nature of the crust under afar new igneous not thinned continental abstract thinned continental crust is considered absent from beneath afar except for isolated remnants such as comprise the danakil block the ethiopian plateau sialic crust thins abruptly across the plateau afar margin to abut new igneous crust under afar generated during the early development of the red sea basin analyses of stretching and sea floor spreading amounts elsewhere in the red sea and gulf of aden basins are employed to support this concept the dual layering of the afar crust and the similarity of p wave velocities in these layers to velocities in sialic crust lead to the proposal that new continental crust can be generated at magmatic rift zones

the red sea 50 years of geological and geophysical research abstract the red sea displays lithosphere that is in transition from rifting to drifting and therefore provides enormous opportunity to understand incipient seafloor spreading development despite more than 50 years of extensive geological and geophysical research there remains significant conjecture concerning the timing of sea floor spreading initiation the extent of spreading along the axis of the red sea and the geodynamic processes responsible for the onset of crustal extension red sea tectonic models based on geological data are dominated by single stage rift models involving protracted stretching of continental crust followed by sea floor spreading at ca 5 ma and include both asymmetric and symmetrical extension models geophysical data suggest that an oceanic crust occurs beneath the red sea shelves although exactly how this crust has evolved remains undecided equally arguments have been made in favor of the sedimentary shelves forming on extended continental crust and that oceanic crust is restricted to the present day red sea axial valley however our synthesis shows that none of the models proposed so far is applicable to the entire red sea basin the distribution and timing of the red sea crustal extension and sea floor spreading may have been influenced by subduction related far field forces due to complex plate interactions along the northern edge of the arabian plate during early miocene our reassessment suggests that following the arrival of the afar plume the southern red sea underwent rapid extension culminating in the transition from rifting to seafloor spreading which stalled during the early miocene in the central red sea due to either slowing of the convergence between arabia and eurasia or the onset of the arabian plate passive margin collision with eurasia off axis magmatism is focused on the arabian margin and afar depression and has been episodically active since the miocene we consider a formation of the red sea as a hybrid process involving both active and passive rifting

probabilistic seismic hazard assessment for the arabian peninsula a seismic hazard evaluation in terms of 5 damped peak ground acceleration and spectral acceleration was carried out for the arabian peninsula using a probabilistic approach for this purpose a revised earthquake catalogue extending from 19 ad to 2015 ad was utilized including all available earthquakes with magnitude greater than 4 0 the seismic hazard assessment was conducted in the framework of the logic tree approach to take into account epistemic uncertainties associated with input parameters seismic source model recurrence parameters maximum magnitude and ground motion prediction equations gmpes a novel seismic source model consisting of 57 seismic zones is proposed as an alternative included in the modeled logic tree the recurrence parameters were computed mainly using the doubly bounded exponential distribution horizontal ground motion in terms of geometric mean acceleration was computed for different spectral periods utilizing gmpes borrowed from tectonic environments comparable to those surrounding the arabian peninsula the 5 damped seismic hazard values at bedrock conditions were calculated for return periods of 475 975 and 2475 years additionally uniform hazard spectra for important population centers in the arabian peninsula are provided the highest seismic hazard values were observed along the zagros the east anatolian fault and the gulf of aqaba dead sea fault the provided maps could be used to design the unified gulf building code

evidence for rapid thinning of sea ice in the western arctic ocean at the end of the 1980s examination of springtime ice drafts obtained from submarine profiles in a narrow band of the western arctic ocean from offshore alaska to 89 n indicates that the mean ice draft decreased 1 5 m between the mid 1980s and early 1990s no similar trend was evident in ice drafts near the north pole the 1980s drafts were composed largely of ice exceeding 3 5 m while the early 1990s drafts contained more ice in thinner categories the differences in drafts between the two periods appear to be related largely to ice dynamics effects associated with the presence and strength of the beaufort gyre which weakened considerably in the early 1990s

strain in shore fast ice due to incoming ocean waves and swell using a development from the theoretical model presented by fox and squire 1990 this paper investigates the strain field generated in shore fast ice by normally incident ocean waves and swell after a brief description of the model and its convergence normalized absolute strain relative to a 1 m incident wave is found as a function of distance from the ice edge for various wave periods ice thicknesses and water depths the squared transfer function giving the relative ability of incident waves of different periods to generate strain in the ice is calculated and its consequences are discussed the ice is then forced with a pierson moskowitz spectrum and the consequent strain spectra are plotted as a function of penetration into the ice sheet finally rms strain computed as the incoherent sum of the strains resulting from energy in the open water spectrum is found the results have implications to the breakup of shore fast ice and hence to the floe size distribution of the marginal ice zone

geomorphology of the central red sea rift determining spreading processes highlights the red sea rift overall morphology is typical for ultra slow spreading ridges distribution of various volcanic morphotypes correlates with mantle temperatures spreading perpendicular ridges indicate stable magma focusing over 8 12 my warm mantle under the rsr prohibits the occurrence of oceanic core complexes specific characteristics of the rsr morphology are related to its young age abstract continental rifting and ocean basin formation is occurring today in the red sea providing a possible modern analogue for the creation of mid ocean ridges yet many of the seafloor features observed along the axis of the red sea appear anomalous compared to ancient and modern examples of mid ocean ridges in other parts of the world making it unclear until recently whether the red sea is truly analogous recent work suggests that the main morphological differences between the red sea rift rsr and other mid ocean ridges are due to the presence and movement of giant submarine salt flows which blanket large portions of the rift valley and thereby the oceanic crust using ship based high resolution multibeam bathymetry of the central rsr between 16 5 n and 23 n we focus here on the rsr volcanic terrains not covered by salt and sediments and compare their morphologies to those observed along slow and ultra slow spreading ridges elsewhere regional variations in style and intensity of volcanism can be related to variations in volcanic activity and mantle heat flow the red sea oceanic seafloor shows typical features of mature ultra slow spreading mid ocean ridges such as 2nd order discontinuities overlapping spreading centres and magma focussing in the segment centres forming spreading perpendicular volcanic ridges of thick oceanic crust the occurrence of melt salt interaction at locations where salt glaciers blanket the neovolcanic zone and the absence of large detachment faults are unique features of the central rsr these features can be related to the young character of the red sea and may be applicable to all young oceanic rifts associated with plumes and or evaporites thus the rsr falls in line with ultra slow spreading mid ocean ridges globally which makes the red sea a unique but highly important type example for initiation of slow rifting and seafloor spreading and one of the most interesting targets for future ocean research

interannual variability of arctic landfast ice between 1976 and 2007 abstractanalysis of weekly sea ice charts produced by the u s national ice center from 1976 to 2007 indicates large interannual variations in the averaged winter landfast ice extent around the arctic basin during the 32 yr period of the record landfast ice cover was relatively extensive from the early to mid 1980s but since then has declined in many coastal regions of the arctic particularly after the early 1990s while the barents baltic and bering seas show increases in landfast ice area the overall change for the northern hemisphere is negative about 12 27 2 8 103 km2 yr 1 or 7 1 5 decade 1 relative to the long term mean except in a few coastal regions the seasonal duration of landfast ice is shorter overall particularly in the laptev east siberian and chukchi seas the decreased winter landfast ice extent is associated with some notable changes in ice growth and melt patterns in particular the slowed landfast ice expansion during fall and early winter since 1990 the observed

substorm onset observations by image fuv 1 over the first 2 5 years of operation the fuv instrument on the image spacecraft observed more than 2400 substorm onsets in the northern hemisphere the observations confirm earlier results of statistical studies in terms of a median substorm onset location at 2300 hours mlt and 66 4 degrees magnetic latitude the purpose of this report is to publish the list to allow for further investigation the list can easily be searched for onsets close to certain ground stations or at specific magnetic latitudes or local times as one example of such use we demonstrate how the probability of onset observation was determined for the ground based automatic observatories of the themis time history of events and macroscale interactions during substorms project

atmospheric driven state transfer of shore fast ice in the northeastern kara sea received 9 september 2004 revised 19 april 2005 accepted 2 june 2005 published 21 september 2005 1 frequencies of observed occurrences of shore fast ice in the northeastern kara sea for each month during 1953 1990 reveal a multimodality of shore fast ice extent in late winter and spring the fast ice extent exhibits mainly three different configurations modes associated with the regional topography of coasts and islands these modes show fast ice areas equal to approximately 98 6 122 6 and 136 8 1000 km 2 analysis of the time series of fast ice extent shows that favorable conditions for expansion of fast ice seaward in winter and spring are met if the atmospheric circulation over the northeastern kara sea is controlled by the arctic high resulting in offshore winds and a significant up to 6 c decrease of the monthly mean surface air temperature in contrast the penetration of the icelandic low into the kara sea accompanied by arctic cyclones coming from the west is responsible for the partial breakup and decrease of fast ice extent in winter or spring

neotectonics of africa and the indian ocean development of the geoidal low abstract the western trans africa lobe of the indian ocean geoidal low correlates with neogene tectonic features such as the east africa rift system and the congo river basin the opposite eastern flank of the indocean geoidal low is indented westward by the geoidal high associated with sundaland indonesia believed to have been displaced westward into its present location since mid tertiary times the indocean low thus seems to be slowly mobile and to have acquired its present shape elbowed at the equator pointing west as a result of tectonic processes continuing at present we have sought lithosphere motion accounting for the large scale tectonics and for the changes in the geoidal low the constraints suggest that africa and the western part of the indian ocean basin have been experiencing slow westward drift in neogene times this has resulted in the development of the mass deficiency to the east expressed as the indian ocean geoidal low in the africa meridional rifting and in seafloor spreading as material upwells from the asthenosphere in response to the developing hydrostatic deficiency the motion is consistent with the seafloor magnetic record and would explain the dextral displacement at the south boundary of the eurasian lithosphere segment

low angle detachment origin for the red sea rift system abstract the tectonic and magmatic history of the jizan coastal plain tihama asir southwest arabia suggests a two stage evolution a first stage of extension began during the oligocene and ended with uplift of the arabian graben shoulder which began about 14 ma ago it was followed by a period of approximately 10 ma characterized by magmatic and tectonic quiescence a second stage of extension began roughly contemporaneously with the onset of seafloor spreading in the southern red sea some 4 5 ma ago and is still active today the geometry of faulting in the jizan area supports a wernicke model of simple shear for the development of the southern red sea regional asymmetries of the red sea area such as the distribution of volcanism the marginal topography and asymmetries in the geophysical signatures are consistent with such a model available seismic profiles allow a rough estimate for values of the arabian red sea margin and were used to simulate subsidence history and heat flow of the red sea for classical two layer stretching models neither finite uniform nor finite non uniform stretching models can account for observed subsidence and heat flow data thus two model scenarios of whole lithosphere normal simple shear are presented for the geological history of the southwestern arabian margin of the red sea these models are limited because of the serravallian rearrangement in the kinematics of the red sea

crustal structure of the rifted volcanic margins and uplifted plateau of western yemen from receiver function analysis we analyse p wave receiver functions across the western gulf of aden and southern red sea continental margins in western yemen to constrain crustal thickness internal crustal structure and the bulk seismic velocity characteristics in order to address the role of magmatism faulting and mechanical crustal thinning during continental breakup we analyse teleseismic data from 21 stations forming the temporary young conjugate margins laboratory yocmal network together with gfz and yemeni permanent stations analysis of computed receiver functions shows that 1 the thickness of unextended crust on the yemen plateau is 35 km 2 this thins to 22 km in coastal areas and reaches less than 14 km on the red sea coast where presence of a high velocity lower crust is evident the average vp vs ratio for the western yemen plateau is 1 79 increasing to 1 92 near the red sea coast and decreasing to 1 68 for those stations located on or near the granitic rocks thinning of the crust and by inference extension occurs over a 130 km wide transition zone from the red sea and gulf of aden coasts to the edges of the yemen plateau thinning of continental crust is particularly localized in a 30 km wide zone near the coastline spatially co incident with addition of magmatic underplate to the lower crust above which on the surface we observe the presence of seaward dipping reflectors sdrs and thickened oligo miocene syn rift basaltic flows our results strongly suggest the presence of high velocity mafic intrusions in the lower crust which are likely either synrift magmatic intrusion into continental lower crust or alternatively depleted upper mantle underplated to the base of the crust during the eruption of the sdrs our results also point towards a regional breakup history in which the onset of rifting was synchronous along the western gulf of aden and southern red sea volcanic margins followed by a second phase of extension along the red sea margin

on the simultaneity of substorm onset between two hemispheres simultaneous observations of auroral kilometric radiation from the northern and southern hemispheres showed some cases in which the buildup of field aligned acceleration occurred only in one hemisphere at the substorm onset this indicates that a substorm does not always complete the current system by connecting the cross tail current with both northern and southern ionospheric currents conjugate auroral observations showed that in one case the auroral breakup in the northern and southern hemispheres was not simultaneous rather they occurred a few minutes apart this time difference in the breakup between two hemispheres suggests that the local auroral ionosphere controls auroral breakup in each hemisphere independently the evidence in this study may indicate that the buildup of the field aligned acceleration region at the auroral breakup does not result only from the magnetospheric process and that the auroral ionosphere finally controls and or ignites the substorm onset that is the auroral breakup

problems concerning the evolution of oceanic lithosphere in the northern red sea abstract the pole of rotation for the opening of the red sea at 36 5 n 18 0 e arabia from africa implies the fastest spreading rates are in the south and are about 50 less in the north various studies show the spreading rate in the south to be about 1 cm yr over the last 4 5 ma problems arise as to the nature of the lithosphere beneath the northernmost red sea the problem is further complicated by the fact that the red sea may have evolved in three phases the first is the gulf of suez phase mainly oligocene the second corresponds to the first 62 km movement along the aqaba dead sea shear latest oligocene early miocene and the third to the second 45 km movement along the aqaba dead sea shear plio pleistocene these motions and their implications for the northernmost red sea are assessed the northern red sea differs from the central and southern red sea in having no clear magnetic lineations only a few isolated circular anomalies are observed there are two possible explanations 1 1 there is extremely thinned continental lithosphere occasionally pierced by strongly magnetised volcanic centres or 2 2 the oceanic lithosphere is present but without magnetic anomalies it is suggested that the first explanation applies to the first gulf of suez phase and the second explanation to the two later aqaba dead sea phases it is further suggested that the lack of magnetic anomalies may be due to a combination of large thicknesses of unstable sediments salt high temperatures and low sea floor spreading rates these lead to the evolution of oceanic lithosphere with slow cooling inhibiting the acquisition of strong magnetisation and giving subdued magnetic anomalies

distribution of branched gdgts in surface sediments from the colville river alaska implications for the mbt cbt paleothermometer in arctic marine sediments significant climate fluctuations in the arctic over the recent past and additional predicted future temperature changes highlight the need for high resolution arctic paleoclimate records arctic coastal environments supplied with terrigenous sediment from arctic rivers have the potential to provide annual to subdecadal resolution records of climate variability over the last few millennia a potential tool for paleotemperature reconstructions in these marine sediments is the revised methylation index of branched tetraethers mbt cyclization ratio of branched tetraethers cbt proxy based on branched glycerol dialkyl glycerol tetraethers brgdgts in this study we examine the source of brgdgts in the colville river alaska and the adjacent simpson lagoon and reconstruct temperatures from simpson lagoon sediments to evaluate the applicability of this proxy in arctic estuarine environments the colville catchment soils fluvial sediments and estuarine sediments contain statistically similar brgdgt distributions indicating that the brgdgts throughout the system are soil derived with little alteration from in situ brgdgt production in the river or coastal waters temperatures reconstructed from the mbt cbt indices for surface samples show good agreement with regional summer june through september temperatures suggesting a seasonal bias in arctic temperature reconstructions from the colville system in addition we reconstruct paleotemperatures from an estuarine sediment core that spans the last 75 years revealing an overall warming trend in the twentieth century that is consistent with trends observed in regional instrumental records these results support the application of this brgdgt based paleotemperature proxy for subdecadal scale summer temperature reconstructions in arctic estuaries containing organic material derived from sediment laden episodic rivers

the rotation of arabia and the levant fault system abstract we establish the kinematics of the rotation of arabia with respect to africa and show that the rotation rate of africa increased by a factor of about four in late serravallian time about 12 13 ma ago we discuss evidence that oceanic accretion started simultaneously in the gulf of aden and in the red sea at this time it is also at this time that the levant and anatolian fault systems were initiated our initial reconstruction of the red sea rift in late oligocene early miocene time approximately superposes the present shore lines which coincide with the mid point of the zones of rapid crustal thinning the future continental slopes the amount of extension during the early phase of continental rifting is obtained by assuming that the total volume of continental crust is conserved during extension and by checking these estimates through closure around the sinai triple junction in the late miocene the southern evant fault zone was a zone of distributed shear deformation through counterclockwise block rotation extending soul h ward within the northernmost red sea since the early pliocene the shear motion has been localized within the gulf of aqaba changing the tectonic pattern in the northern red sea

the rifting to spreading transition in the red sea highlights the red sea rift rsr comprises the typical terrain of slow mor axes seen elsewhere submarine salt glaciers occur extensively along the rsr and blanket parts of the rsr inter trough zones are not continental but oceanic crust covered by evaporite flows we see a global mechanism for spreading initiation and no need for a multi node model we see prospects for large mineral deposits at passive margins that host evaporites abstract the transition from continental rifting to seafloor spreading is presently occurring at only a few places on earth such as the red sea or the woodlark basin competing theories for how spreading begins either by quasi instantaneous formation of a whole spreading segment or by initiation of spreading at multiple discrete nodes separated by thinned continental lithosphere have been put forward the major evidence for the nodes theory comes from the red sea and geophysical surveys carried out there in the multi deeps region during the 1970 s and 1980 s we present new high resolution multibeam bathymetric information over the same region which when combined with acoustic backscatter data seafloor sampling and magmatic geochemical information appears to provide no support for the nodes model we show that although the discrete deeps undoubtedly exist they are not separated from one another by tectonic boundaries but rather represent windows onto a continuous spreading axis which is locally inundated and masked by massive slumping of sediments and evaporites from the rift flanks the geophysical data that was previously used to support the presence of continental crust between the nodes can be equally well explained by processes related to the sedimentary blanketing and sub sedimentary hydrothermal alteration a single quasi instantaneous segment formation model would appear to be all that is required to explain observations from present day rifting spreading transitions globally

the tethys sea and the alpine himalayan orogenic belt mega elements in a new global tectonic system abstract analysis of meso cainozoic palaeomagnetic data for africa india and eurasia has led to the development of a new mobilistic alpine plate tectonic model characterized by a hierarchical system of plates in relative rotation the new model which discounts seafloor spreading implies that there have been no significant palaeogeographic changes in the overall distribution of continental and oceanic regions the mid oceanic ridges are interpreted as transpressive tectonic features caused by rotation of megaplates containing both continental and oceanic crust the isostatic uplift due to crustal lithospheric thickening giving rise to the general ridge topography as well as to the ridge parallel structural grain the new plate tectonic theory gains strong support from a variety of geophysical geological and palaeoclimatological evidence and several observations that have remained enigmatic or awkward within the context of the orthodox model can be readily accounted for in the new tectonic framework the model maintains the tethys as a relatively narrow epicontinental sea which during its maximum extent stretched latitudinally from the caribbean across the central atlantic to se asia the alpine himalayan orogenic belt developed along the boundary of two megaplates in relative rotation which provided a transpressive tectonic regime the location of the plate boundary to the north of the mediterranean has important implications for discussion of mediterranean microplates for example it now seems that italy has been subjected to 10 15 of clockwise microplate rotation previous conclusions in favour of 30 40 of anticlockwise rotation are regarded as artefacts which arise from incorrectly linking the mediterranean region to the european palaeomagnetic frame instead of to the african one the model suggests further that the indo pakistani plate was closely tied to eurasia this challenges the conventional view that the peninsula was part of an alleged gondwanaland the new pre drift configuration implies that the indo pakistani plate rotated 135 clockwise at around the cretaceous tertiary boundary before redocking with asia in approximately its present relative orientation

seismicity and tectonics of the red sea and western arabia summary search in a number of seismological sources revealed that in the period 1913 86 some 135 earthquakes 3 m s 6 9 occurred in the red sea and western arabia between latitudes 14 and 27 2 n in the same period 49 earthquakes m s 6 9 and 247 earthquakes m c 4 9 are reported to have occurred in the gulfs of suez and aqaba respectively twenty three historical earthquakes are reported to have been felt in the region with intensities iv ix and a few more with unassigned intensities during the period ad 627 1884 the epicentral distribution of both instrumental and historical data and their characteristics show a general correlation with the regional geology and tectonics sixty per cent of the total energy released from all instrumental earthquakes is released from earthquakes epicentred within the spreading zone concentrations of activity are seen where the spreading zone is intersected by the ne transform faults and where this zone shifts in direction much of the seismicity of this region is of the swarm type and volcanic related both instrumental and historical data show an apparent lower seismicity in the northern red sea region between latitudes 22 and 27 2 n but the whole region is of a noticeable seismic risk that is mostly associated with regional land faults some of which are continuations of the red sea transform faults the instrumental seismicity of the whole region conforms with the relation log n 4 23 0 53m when historical data are considered both datasets conform with the relation log n 4 1 0 47m the b constant correlates with the shield type of environment and seems to increase gradually northwards to attain a value of 0 71 in the gulfs region this may be caused by either heterogeneity in the lithosphere or most probably asymmetry of the regional stress field in the vicinity of latitude 27 5 n or both causes

crustal thinning in relationship to the evolution of the afro arabian rift system a review of seismic refraction data abstract crustal and upper mantle structure of major units of the afro arabian rift system has been progressively investigated by seismic refraction surveys in the jordan dead sea rift the red sea the afar depression and in the east african rift of kenya the two extreme structures are oceanic crust flooring the axial trough of the southern red sea rift and 30 35 km thick continental crust underneath the jordan dead sea rift and its flanks underlain by a mantle with pn velocities of 8 0 8 2 km s the remainder of the units have a crustal structure of transitional to uncertain nature in the southeastern red sea the change from 15 18 km thick transitional crust to the 40 km thick continental crust of the arabian shield is probably very abrupt and is the major lateral change in structure in this region in the northern afar depression the crust is only 15 20 km thick in the southern afar depression anomalous mantle with 7 2 7 3 km s velocities occurs at depths greater than 25 km also here an abrupt change to a 40 km thick shield crust with a velocity of 8 0 km s is evident from seismic and gravity data crustal thickness of the east african rift system amounts to 30 36 km a recent trial experiment in the eastern rift of kenya indicates a 35 36 km thick crust underlain by a low velocity upper mantle with 7 5 km s at 23 24 km depth a thin high velocity lens of 7 1 km s velocity may be present within the 22 km thick lower crustal layer averaging 6 6 km s velocity investigations of local earthquake body waves in the western rift provide information that the crust here is of continental type with a thickness of about 32 km overlying mantle material of 8 0 km s p velocity and 4 6 km s s velocity in conclusion a model of preferential rifting of continents is applied to the afro arabian rift system where rifting seems to progress into areas with thick continental crust as seen for example in the levant and the east african rift systems instead of using paths in thin crust

episodic sea floor spreading in the southern red sea abstract the red sea represents the most spectacular example of a juvenile ocean basin on the modern earth synthesis of regional aeromagnetic data gravity data seismic refraction data coupled with structural mapping from the farasan islands suggest that the opening of the red sea is complex and episodic modeling of magnetic and gravity data constrained by seismic refraction data reveals the arabian shelf is underlain by oceanic and transitional crust and that mafic diking and intrusions are focused at the continental transitional crust boundary this relationship is interpreted to indicate that early miocene diking along the arabian escarpment heralded termination of oceanic basin formation and a shift in the locus of extension focused from a central mid ocean ridge spreading center to the continental transitional crust zone uplift along the arabian escarpment caused erosion and middle to late miocene sedimentation of the farasan bank onto existing oceanic crust suggesting that the extensive sedimentary banks of the southern red sea are not passive margins re initiation of spreading occurred at ca 5 ma pliocene to pleistocene shelf reef systems farasan islands developed on the flanks of the spreading ridge are extensively overprinted by normal faults suggesting that not all crustal extension is accommodated by active spreading

shear controlled evolution of the red sea pull apart model abstract results of seismic and other geophysical investigations suggest that strike slip processes controlled the break up of the arabian plate from africa and initiated the red sea rift early oceanisation was facilitated by nucleation of pull apart basins and massive intrusives the evolution of the red sea has gone through different stages it was a zone of structural weakness already during the pan african orogeny approximately 600 ma a major reactivation however that gradually led to the present day configuration was initiated during the late oligocene with intense magmatic activity and the development of a continental rift wrench faulting played a key role in the early evolution of the red sea as it shaped most of its western flank as a sharp plate boundary and resulted in the generation and rapid oceanisation of linearly arranged pull apart basins spatial distribution of these basins reflects the geometry of the strike slip zone which was controlled by pre existing fault systems like the najd shear system the central african fault zone or the onib hamisana and baraka suture zones strike slip motion along the latter zones of weakness influenced mainly the egyptian and sudanese coastal areas arabia was therefore separated from africa by oceanisation in those regions where pull apart basins developed they were still connected in the in between segments by stretched continental crust with arabia as the moving and africa as the stable plate the eastern red sea flank was formed by pure shear through stretching thinning and diffuse extension as a consequence the eastern and western flanks of the red sea are asymmetrical the acceleration of the movement of arabia in early middle miocene could no longer be accommodated by the opening in the gulf of suez and consequently the dead sea strike slip fault developed approximately 14 ma ago since plate motion was still oblique to the major structural trends the pull apart evolution on the western flank continued and the oceanisation was accentuated while in the north the eastern flank developed en echelon fractures of aqaba orientation seafloor spreading commenced 5 ma ago at parts of the central and southern red sea this final stage is also responsible for the bathymetry with maximum depth values of 3000 m in the seafloor spread areas and a much shallower basin in the north the metalliferous red sea deeps are either associated with this infant mid ocean ridge or with the en echelon fractures in the north

coastal landfast sea ice decay and breakup in northern alaska key processes and seasonal prediction 1 seasonal breakup of landfast sea ice consists of movement and irreversible ice detachment in response to winds or oceanic forces in the late stages of ice decay the breakup process of landfast sea ice in the chukchi sea at barrow alaska was analyzed for the years 2000 through 2010 on the basis of local observations of snow and ice conditions weather records image sequences obtained from cameras coastal x band marine radar and satellite imagery we investigated the relation of breakup to winds tides and nearshore current measurements from a moored acoustic doppler current profiler two breakup modes are distinguished at barrow on the basis of the degree of ice decay mechanical breakup due to wind and oceanic forces follows ablation and weakening of the ice thermal breakup is the result of ice disintegration under melt ponds requiring little force to induce dispersion grounded pressure ridges are pivotal in determining the breakup mode the timing of thermal breakup of the nearshore ice cover was found to correlate with the measured downwelling solar radiation in june and july this linkage allows for the development of an operational forecast of landfast ice breakup results from forecasts during 2 years demonstrate that thermal breakup can be predicted to within a couple of days 2 weeks in advance the cumulative shortwave energy absorbed by the ice cover provides for a measure of the state of ice decay and potential for disintegration discriminating between the two modes of breakup bears the potential to greatly increase forecasting skill

red sea related history of extension and magmatism in the jizan area southwest saudi arabia indication for simple shear during early red sea rifting the tectonic and magmatic history of the jizan coastal plain of the red sea tihama asir in southwest saudi arabia is dominated by sw ne extension this extension manifests itself by a basic dike swarm and several generations of normal faults that trend roughly nw se the oldest synrift deposits are non marine clastics and bimodal volcanics of the jizan group which were intruded by basic dikes gabbros and granophyres of the tihama asir magmatic complex tamc radiometric ages for the tamc rocks range from 26 to 18 ma rifting in the southern part of the red sea system therefore is certainly older than 26 ma between 26 and 20 ma the southwestern arabian margin was affected by a monoclinal downwarp flexure the oldest extensional features in the jizan area are n s to nnw sse striking dikes and normal faults which were overprinted by other nw se striking extension structures an array of en echelon extensionzones is linked by complex patterns of transfer faults mainly wnw ese striking dextral strike slip or oblique slip faults the observed superposition of dikes and normal faults of different orientations was not necessarily caused by a counterclockwise rotation of the regional stress field but more likely reflects the clockwise rotation of individual faultbounded blocks between the two phases of extension uplift of the graben shoulder east of the jizan coastal plain is probably younger than 14 ma and its development coincides with a major rearrangement of the kinematics along the red sea this new kinematic pattern probably led to the onset of strike slip movement along the aqaba levant transform at the same time extension and volcanism ceased in the jizan area or shifted further to the west after a long hiatus of about 10 ma renewed extension facilitated extrusion of alkali olivine basalts since 2 ma ago