a geomagnetic excursion in the brunhes epoch recorded in new zealand basalts abstract anomalous geomagnetic directions are recorded in the thermoremanent magnetisation trm of alkali basalt lavas from the auckland volcanic field new zealand the concordance of paleomagnetic directions both in different sites from individual eruptive centres and in sites from several different centres as well as their relatively short age span compared with that of the field as a whole indicates that these anomalous directions have a geomagnetic origin the directions which are dated between approximately 25 ka and 50 ka do not represent full reversals of the geomagnetic field and are interpreted as excursions very few excursions have been reported from the southern hemisphere this is the first such record known from igneous rocks and further supports the notion that excursions are global phenomena the excursions here are tentatively correlated with those reported from lake mungo mono lake and laschamp

an observational study of a coastal barrier jet induced by a landfalling typhoon abstractin this study the structure and evolution of a coastal barrier jet cbj along the east coast of taiwan is documented using operational doppler radars the formation of the cbj was control

plate convergence foreland development and fault reactivation primary controls on brine migration thermal histories and trap breach in the timor sea australia during the latest miocene and early pliocene 5 5 mabp the collision of the australian and eurasian plates resulted in proto foreland development and significant structural reactivation in the timor sea north western australia flexural extension resulting from the down warping of the australian plate into the developing timor trough resulted in the dilatation of the major jurassic and older extensional faults and the formation of shallow mio pliocene fault arrays an integrated multidisciplinary study of hydrocarbon traps from this region using 2 d and 3 d seismic data stable isotope geochemistry fluid inclusion measurements and apatite fission track data has revealed that this fault reactivation produced three categories of traps high hit moderate mit and low lit integrity traps these have characteristic hydrocarbon fill spill fluid flow and thermal histories in mits and lits the dilatation was moderate to intense respectively and allowed hot 90 130 c highly saline 200 000 ppm salinity brines from deep palaeozoic evaporites to migrate up the reactivated faults and chemically and thermally affect the reservoir and shallower intervals apatite fission track data suggest that fluid migration lasted for between 100 000 and one million years in the case of the mits but for only 10 000 100 000 years in the lits this major fluid flow event resulted in the development of a prominent localised late tertiary heating spike in the mits which can significantly affect the accuracy of modelled thermal histories in the lits the thermal effect is less marked due to the more transient nature of the fluid flow event hits were largely unreactivated and hence conduits for brine migration from depth were absent consequently these traps are the most representative of the thermal histories of the source rock depocentres where mits or lits were charged the associated loss of fault seal integrity facilitated hydrocarbon loss from the mesozoic reservoirs which co migrated with the brines up through the mio pliocene fault network upon entering a shallow clastic aquifer system the eocene grebe formation bacterial oxidation of the hydrocarbons liberated co2 which in turn resulted in significant and very isotopically light carbonate cementation this cementation produces sufficient acoustic impedance with the surrounding uncemented sands that it allows these hydrocarbon related diagenetic zones hrdzs to be mapped seismically since both the size and acoustic response of the hrdzs are directly proportional to the amount of hydrocarbons that have leaked from the traps their presence or absence provides a powerful indicator predrill of both trap integrity and the likely thermal regime that that traps have experienced an important observation is that the leaky fault segments over partially breached traps typically only extended for 200 1000 m whereas over the breached traps leaky segments extended for 3000 5000 m consequently exploration programs acquiring remote sensing geochemical data such as geochemical sniffer and airborne laser fluorosensor alf techniques should have closely spaced line spacings if leaky potentially commercial fields are to be detected reliably potential analogues exist between the processes documented during hrdz formation namely the mixing at shallow depths of basinal brines hydrocarbons and connate waters and processes occurring during the formation of pb zn and other low temperature ore deposits

climatology of barrier jets along the alaskan coast part i spatial and temporal distributions abstract this paper investigates the temporal and spatial climatology of coastal barrier jets in the gulf of alaska the jets are divided into two categories based upon the origin of the air involved classic barrier jets fed primarily by onshore flow and hybrid jets fed primarily by gap flow from the continental interior the analyses are compiled from five years 1998 2003 of synthetic aperture radar images from the radarsat 1 satellite totaling 3000 images thermodynamic and kinematic data from the ncep reanalysis is used in the interpretation of the results the majority of coastal barrier jets occur during the cool season with the coastline near mount fairweather and the valdez cordova mountains experiencing the greatest number of barrier jets hybrid jets are even more strongly restricted to the cool season and are commonly found to the west of cross sound yakutat bay and icy bay some interannual variability in the total number of jets is observed coastal barrier jet formation is associate

seismic and stratigraphic evidence for reef expansion and onset of aridity on the northwest shelf of australia during the pleistocene abstract modern reef the great barrier reef and ryukyu reef distribution in the indo pacific region is strongly controlled by warm currents east australian and kuroshio currents that radiate from the indo pacific warm pool the modern distribution of reefs south of 15 s on the western australian shelf is related to the presence of the warm leeuwin current however the age of the reefs south of 15 s and hence their temporal relationship to the leeuwin current has been largely unknown seismic and subsurface stratigraphic data show that reef growth and expansion on the northwest shelf of australia began in the middle pleistocene 0 5 ma the oldest ooids in the region are approximately synchronous with reef growth we suggest a two stage process for the spread of reefs to higher latitudes on the western australian coast first an increase in leeuwin current activity at approximately 1 ma brought warm waters and a tropical biota to the region and second increased aridity after 0 6 ma led to a decline in clastic input and increased alkalinity triggering ooid formation and reef expansion to higher latitudes associated with the switch to higher amplitude glacio eustatic cycles at the end of the middle pleistocene transition the timing and mechanisms for reef expansion south along the western australian coast has implications for the origin of the eastern australian middle pleistocene great barrier reef the new caledonia barrier reef and japanese ryukyu reef systems

methane derived authigenic carbonates mdac in northern central adriatic sea relationships between reservoir and methane seepages abstract in the adriatic basin gas venting characterized by pockmarks gas bubbling and other fluid escape related features is diffused and has been linked or to shallow gases trapped in the late pleistocene and below the holocene maximum flooding surface or to leakage from more deeply buried pliocene to pleistocene foredeep succession some seepages are associated with carbonate crusts but a possible correlation between methane leakage and carbonate precipitation in this basin never reached a clear definition carbonate concretions recovered by different areas of the adriatic sea northern central and southern at different depths from ca 30 to ca 300 m have been analysed different fabrics petrography and mineralogy can be evidenced for the different sets of samples all of them show a carbonate content mainly represented by high mg calcite up to 66 in weight of total carbonates for the samples from central adriatic close to bonaccia gas field offshore ancona and 79 to 96 of the total carbonate weight for the other samples that are mainly biogenic these differences are also reflected by the 13 c values ranging between 19 and 29 vpdb for the samples collected in the bonaccia area and moderately positive values for all the other samples bonaccia samples contain carbonate cements that record the contribution of methane derived carbon and have been interpreted as formed below the sea floor in correspondence of the sulphate methane transition zone carbonates recovered from the southern and northern adriatic basin do not show clear evidence of methane derived carbon and are mainly made up by organisms typically recovered in the adriatic coralligenous assemblage nonetheless micro morphological evidences suggest influence of bacterial sulphate reduction and methanogenesis in precipitation of some of these carbonates

the nature and hydrogeologic significance of mud diapirs and diatremes for accretionary systems in accretionary wedges often morphologically similar sedimentary intrusions when observed by remote geophysical means may have one of two quite different driving mechanisms and a highly variable significance for the regional hydrogeologic picture for example mud diapirs are driven by buoyancy forces that arise from bulk density contrasts in them mud and pore fluid upwell en masse and fluid migration is a related sometimes important but generally subsidiary process in contrast diatremes contain sediments fluidized during rapid fluid advection and are forcibly and directly driven by the hydrogeologic system the nature of fluid input from local and exotic source regions can therefore strongly affect sedimentary intrusive processes and vice versa this complicates the process of defining the main features of the hydrogeological systems operating in accretionary wedges focused vertical advection through steep sided piercement mud diapirs requires conduit systems otherwise flow will be diffuse and directed more horizontally out of the low permeability mud mass however where the permeability of the overburden is less than that of the diapir the whole diapir may act as a conduit apart from this special case conduits will be associated with highly anisotropic scaly fabrics that can sometimes develop in the marginal shear zone of diapirs scaly fabrics form during deformation and compaction of a mud matrix under conditions of constant or increasing effective stress however the effective stress path can be complex as it is both controlled by the relative rates of upward intrusion and burial by sedimentation and or structural thickening and the hydrogeologic system due to this it appears likely that even in a geographically related group of diapirs effective stress histories will vary widely between intrusions so that some can form advective pathways for fluids and some cannot mixed systems of behavior may also be present with local diatremes developing within diapirs above the terminations of conduit systems and rapidly expanding methane gas pockets the potentially heterogeneous near surface behavior may be why the surface manifestations of sedimentary intrusions are so variable when observed in the field diatremes can also form separately as large primary features above any structural or stratigraphic conduit that rapidly expels water or gas into the base of an unlithified sediment column when active large diatremes require enormous quantities of fluid water or gas to drive them particularly if they are long lived features and hence are a direct indication of at least an episodically vigorous hydrogeologic system

a multiwinter analysis of channeled flow through a prominent gap along the northern california coast during caljet and pacjet abstract experimental observations from coastal and island wind profilers aircraft and other sensors deployed during the california land falling jets experiment of 1997 98 and the pacific land falling jets experiment of 2000 01 2003 04 were combined with observations from operational networks to document the regular occurrence and characteristic structure of shallow 400 500 m deep cold airstreams flowing westward through california s petaluma gap from the central valley to the coast during the winter months the petaluma gap which is the only major air shed outlet from the central valley is 35 50 km wide and has walls extending at most a modest 600 900 m above the valley floor based on this geometry together with winter meteorological conditions typical of the region e g cold air pooled in the central valley and approaching extratropical cyclones this gap is predisposed to generating westward directed ageostrophic flows driven by along gap pressure differences two case studies and a fiv

magnetostratigraphic data from late quaternary sediments from the yermak plateau arctic ocean evidence for four geomagnetic polarity events within the last 170 ka of the brunhes chron summary palaeomagnetic investigations of two sediment cores recovered from rv polarstern near the eastern slope of the yermak plateau sites ps 1533 and ps 2212 reveal convincing evidence for four polarity events of the earth s magnetic field during the last 170 ka a comprehensive rock magnetic study of the sediments proved that fine grained magnetite is the principal carrier of the remanent magnetization no changes in magneto mineralogy across the polarity transitions in the sediments investigated were found calcareous nannofossil biostratigraphy ams 14c accelerated mass spectrometry and oxygen isotope data and 10be and 230th stratigraphies yielded age ranges of 24 29 ka for the mono lake event 34 43 ka for the laschamp event 72 86 ka for the norwegian greenland sea event and 118 128 ka for the blake event two reverse polarity samples at the base of core ps 2212 3 kal are interpreted as the termination of the biwa i event 171 181 ka the events exhibit full inversion of inclination in both cores the data suggest that the transition process of the earth s magnetic field during such polarity events requires some 1 ka

a numerical study on the effects of taiwan topography on a convective line during the mei yu season abstract during the morning hours on 23 may 2002 a convective line associated with a mei yu front brought heavy rainfall along the coast of central taiwan under favorable synoptic conditions of warm air advection and large convective available potential energy cape of over 3000 m2 s 2 doppler radar observations indicated that deep convection was organized into a linear shape with a northeast southwest orientation along the front about 70 km offshore from taiwan over the northern taiwan strait the system then moved toward taiwan at a slow speed of about 4 m s 1 in the present study the effects of taiwan topography on this convective line and subsequent rainfall distribution were investigated through numerical modeling using the nagoya university cloud resolving storm simulator cress at a 2 km horizontal grid size experiments with different terrain heights of taiwan including full terrain ftrn half terrain htrn and no terrain ntrn were performed the control run using full terrain and co

a genetic model of hydrocarbon derived carbonate chimneys in shelfal fine grained sediments the enza river field northern apennines italy abstract methane derived authigenic carbonate mdac concretions have been recently exposed in the pleistocene argille azzurre fm outcropping along the enza riverbanks northern apennines foothills italy the relations between the sediment deposition the coeval tectonic deformation and the mdac concretions have been investigated to unravel the mechanism of methane migration through the sediments and the processes leading to mdac occurrence the biogenic methane responsible for the formation of mdac chimneys and slabs has been generated in the organic rich pliocene sediments located in the po plain subsurface the gas migrated up dip towards the northern apennines foothills the mdac cements are mainly composed of dolomite whose precipitation requires thousand years and the absence of so 4 in the pore fluids according with the sedimentation rates of the mdac hosting pleistocene succession the sulphate methane transition zone migrated upwards faster than time required for dolomite precipitation therefore the connate water migrating together with the methane could have acted as second dic source allowing the mdac formation also in the methane rich zone

carbonate mounds from paradox to world heritage the recent marine carbonate world comprises two major compartments 1 the surface domain of the photozoan carbonates confined in space by water depth and by the penetration of light and 2 a deep domain where heterozoan mound builder guilds directly forage on fluxes of nutrients which primarily percolate from the photic zone and or are generated by in situ benthic processes locally giant cold water coral mounds tower up to heights of 150 to 250 m above the sea floor in general between 500 and 1300 m water depth and within sharply delineated provinces some 15 years of research on these giant mound provinces conveys a picture of their distribution in space and possibly sheds light on controls acting in concert globally there is no counterpart for the prolific north atlantic mound basin namb a chemical control is seen by an overlay of the mound provinces on a map of the aragonite saturation horizon ash an external physical control is inferred fromthe position of themound provinces girdling a vigorous north atlantic subtropical gyre systemand clustering close to the roof of the intermediate to deep water masses of a dynamically stratified ocean on the eastern boundary of the namb nutrient fluxes are enhanced by mixing processes driven either by internal waves between galicia and the shetlands or by the vast and heterogeneous eastern boundary upwelling system along the iberian african margins down to 10 n early diagenesis by carbonate dissolution and re precipitation driven by convecting or advecting internal fluids can contribute to stabilize such constructions facilitating an exuberant vertical accretion it is speculated that in thenorth atlantic ocean the deep water carbonate factory outclasses in size the shallow water coral reefs giant mound formation is a recurrent play of life since the dawn of the metazoans nama group upper neoproterozoic however with actors and plots varying from act to act remarkably literature reports only three occurrences of deep water mounds in the phanerozoic the modern ocean possibly the danian and the carboniferous some striking parallelisms in the development of the atlantic and the paleo tethys oceans combined with the developing insights in the controls on deep watermounds in the present ocean invite for a comparative study this has the potential to eventually shed light on the full circulation pattern of the paleo tethys ocean surface and deep comparative studies will build upon 1 modeling of ocean circulation constrained by the record of deep water carbonate systems and supported by advances in tracer and proxy tools and 2 field studies on representative and accessible continental locations the mound route that develops in morocco under the auspices of ioc unesco will provide tomulti disciplinary teams with marine and continental experience opportunities for confronting observations from the modern ocean and on key records of past oceanic basins it has the potential to eventually qualify for a unesco recognition as world heritage

10be records of sediment cores from high northern latitudes implications for environmental and climatic changes the 10be records of four sediment cores forming a transect from the norwegian sea at 70 n core 23059 via the fram strait core 23235 to the arctic ocean at 86 n cores 1533 and 1524 were measured at a high depth resolution although the material in all the cores was controlled by different sedimentological regimes the 10be records of these cores were superimposed by glacial interglacial changes in the sedimentary environment core sections with high 10be concentrations 1 109 at g are related to interglacial stages and core sections with low10be concentrations 0 5 109 at g are related to glacial stages climatic transitions e g termination ii 5 6 are marked by drastic changes in the 10be concentrations of up to one order of magnitude the average 10be concentrations for each climatic stage show an inverse relationship to their corresponding sedimentation rates indicating that the 10be records are the result of dilution with more or less terrigenous ice rafted material however there are strong changes in the 10be fluxes e g termination ii into the sediments which may also account for the observed oscillations most likely both processes affected the 10be records equally amplifying the contrast between lower glacials and higher interglacials 10be concentrations the sharp contrast of high and low 10be concentrations at climatic stage boundaries are an independent proxy for climatic and sedimentary change in the nordic seas and can be applied for stratigraphic dating 10be stratigraphy of sediment cores from the northern north atlantic and the arctic ocean

geographical distribution of transitional vgps evidence for non zonal equatorial symmetry during the matuyama brunhes geomagnetic reversal abstract paleomagnetic records of the matuyama brunhes polarity reversal obtained recently from the northern equatorial and southern latitudes of the atlantic sector display a distinct symmetry with respect to the equator the virtual geomagnetic pole vgp paths from the mid latitude sites in the northern and southern hemispheres dsdp site 609 and core v16 58 are nearly coincident tracking northward through the americas the vgp path from the equatorial site odp site 664 tracks northward through eastern asia nearly antipodal to the other two paths modeling results indicate that superimposing an h 1 3 geometry onto a reversing axial dipole explains the sense of equatorial symmetry exhibited by these three records these results are consistent with the bulk of the data available from other records of this polarity transition suggesting that the transitional vgps during this reversal tend to fall along two distinct longitudinal bands the grouping of transitional vgps suggests that there is a strong geographical control over the reversal process an apparent correlation between the longitudinal bands of transitional vgps and the location of the major flux concentrations in the radial component of the historical geomagnetic field at the core mantle boundary 1 suggests that the processes which cause these flux concentrations may have influenced the geometry of the matuyama brunhes transitional field

on the origin of atmospheric frontal lines off the east coast of taiwan observed on spaceborne synthetic aperture radar images abstract frontal lines having offshore distances typically between 40 and 80 km are often visible on synthetic aperture radar sar images acquired over the east coast of taiwan by the european remote sensing satellites 1 and 2 ers 1 and ers 2 and envisat in a previous paper the authors showed that they are of atmospheric and not of oceanic origin however in that paper they did not give a definite answer to the question of which physical mechanism causes them in this paper the authors present simulations carried out with the fifth generation pennsylvania state university national center for atmospheric research mesoscale model which shows that the frontal lines are associated with a quasi stationary low level convergence zone generated by the dynamic interaction of onshore airflow of the synoptic scale wind with the coastal mountain range of the island of taiwan reversed airflow collides with the onshore flowing air leading to an uplift of air which is often accompanied by the formation of bands

the effects of a mountain on the propagation of a preexisting convective system for blocked and unblocked flow regimes abstract observations and previous research of squall lines impinging on mountain ranges have revealed that the squall lines sometimes stall upstream of the mountains for several hours leading to copious accumulations of precipitation it has been hypothesized that squall line stagnation may be more prone to occur in flows where the froude number f u nh where u is the basic state wind n is the brunt vaisala frequency and h is the mountain height is low this hypothesis is tested herein through a series of idealized two dimensional experiments where a convective system was triggered upstream of a mesoscale mountain in conditionally unstable flow for simulations with relatively low froude numbers stagnation of the preexisting convective system was not observed in the simulations with high values of f squall lines were noted to stagnate between 100 and 200 km upstream of the mountain this result indicates that squall line stagnation may be more favored for moderate to large values of f for condi

formation of a coastal barrier jet in the gulf of mexico due to the interaction of cold fronts with the sierra madre oriental mountain range the passage of tree cold fronts cfs over the gulf of mexico were simulated with the weather research and forecasting model to study the mechanisms associated with the formation of a jet parallel to the sierra madre oriental smor mountain range near the port of veracruz dew point temperature td 20 c and available convective potential energy best simulated the horizontal propagation of the intense cfs over the gulf and equivalent potential temperature helped identify the vertical position of the fronts additional simulations with reduced topography showed that mountain heights exceeding 2 5 km where the smor is closest to the coast were crucial for the formation of a coastal barrier jet the froude number fr 18 ms 1 and occurred near the surface 1 km amsl consistent with observations and similar to other barrier jets in the world for the first time the jet near the port of veracruz is documented as a coastal barrier jet the cfs also produced strong tehuano gap winds

orographic precipitation isotopic ratios in stratified atmospheric flows implications for paleoelevation studies an idealized fully nonlinear atmospheric model was used to evaluate the effects of stratified atmospheric flows on orographic precipitation isotopic ratios with the aim of improving the foundation for interpreting proxy records used for paleoelevation studies orographic precipitation isotopic ratios can be understood in terms of two nondimensional parameters the flow parameter nh u where n is the moist brunt vaisala frequency a measure of atmospheric stratification h is the large scale relief and u is the upstream horizontal wind speed perpendicular to the orogen and the horizontal aspect ratio the ratio of the along strike length of the orogen to its across strike width existing rayleigh condensation models for paleoaltimetry studies are only strictly applicable when nh u 0 much of the time high values of both nh u and favor precipitation upstream of the terrain leading to isotopic ratios that are more depleted than predicted by the rayleigh model high nh u and low favor low level deflection of winds around the terrain which substantially reduces lifting and condensation leading to precipitation isotopic ratios in that are less depleted than predicted by the simple rayleigh model changes in climate or the horizontal terrain aspect ratio can change precipitation isotopic ratios at least as much as changes in surface elevation and surface uplift need not always affect precipitation isotopic ratios suggesting that proxy records must be interpreted within a broad context of climate variability and landscape evolution

observations and scale analysis of coastal wind jets abstract blocking of onshore flow by coastal mountains was observed south of vancouver island british columbia by the noaa p 3 aircraft on 1 december 1993 winds increased from 10 m s 1 offshore to 15 m s 1 nearshore and became more parallel to shore in the blocked region which had a vertical scale of 500 m and an offshore scale of 40 50 km these length scale and velocity increases are comparable to theory the flow was semigeostrophic with the coast being hydrodynamically steep that is the coast acts like a wall and the alongshore momentum balance is ageostrophic this is shown by the nondimensional slope parameter the burger number b hmn flm being greater than 1 where hm and lm are the height and half width of the mountain n is the stability frequency and f is the coriolis parameter the height scale is given by setting the local froude number equal to 1 that is hl u n 500 m where u is the onshore component of velocity this scale is appropriate when hl is less than the mountain height

synoptic and topographic variability of northern california precipitation characteristics in landfalling winter storms observed during caljet abstract observations from northern california during the california landfalling jets caljet experiment are used to examine the mean characteristics of precipitation and their variances as functions of synoptic and topographic regimes ten cases involving the landfall of extratropical cyclones are analyzed with radar and rain gauge data collected at two sites one in the coastal mountains north of san francisco czd and the other in the central valley just west of sacramento kdax aside from the melting layer bright band the most striking feature in the 10 case composite vertical profile of radar reflectivity at czd was a distinct change in slope about 2 5 km above the bright band this shoulder is thought to represent a change in the growth rate of hydrometeors although the bright band was quite distinct about one third of the profiles in the composite did not exhibit this feature these nonbrightband nbb profiles had a low level slope where reflectivity increased with decreasing altitude a

evolution of the hourglass structures in the laminaria high timor sea implications for hydrocarbon traps abstract in cross section an hourglass structure can be visualized as an older horst block and superimposed younger graben bounding faults of the horst and graben blocks represent separate conjugate fault systems formed by two distinct episodes of extension in the timor sea during late jurassic early cretaceous 1st phase and middle miocene pliocene 2nd phase with an 120 my hiatus of limited or no fault activity in between horst blocks were formed by the 1st phase of extension and buried post deformation with the onset of the 2nd phase of extension the hourglass geometry began to form by nucleation of the graben bounding faults in the shallow sedimentary section in isolation from the horst bounding faults location of the graben is biased by the buried horst block and graben bounding faults grew down dip from the shallow locus of nucleation toward the underlying horst block on which only minor reactivation occurred detachment of the two systems in this way was predominantly controlled by the first order mechanical layering a thick shale rich ductile layer separates the horst and graben bounding fault systems and acts as a barrier to vertical fault propagation confinement of the graben bounding faults into the shallow section was also facilitated by outer arc style extension due to lithospheric flexure controlling the 2nd phase strain in the region the complex evolution history and the composite nature of the hourglass structures resulted in systematic along dip variation of displacement this variation predominantly relates to syn kinematic deposition and location of fault tips that are controlled by the ductile layer the presented evolution model of the hourglass structures concentrates fault tips and related stress perturbation onto the top seal and is likely to be detrimental to top seal integrity

high resolution record of the upper olduvai transition from po valley italy sediments support for dipolar transition geometry abstract a detailed record of the upper olduvai polarity transition composed of 100 transitional directions has been obtained from the crostolo section in northern italy a careful examination of the rock magnetic properties of the sediments using standard paleomagnetic techniques thermomagnetic scanning electron microscopy microprobe x ray diffraction and mossbauer analysis shows that greigite is the main magnetic carrier of the remanence the correlation of a shift in the magnetic record to a small scale sedimentary feature observed in the section indicates that the magnetization was acquired at deposition or very shortly after the virtual geomagnetic pole vgp path is largely confined along a great circle over north and south america 90 west of the site and consists of three stages first the vgp moves to southern mid latitudes then after a period of standstill it comes back to almost true north and finally the south pole is reached in a third step although different from a record from the southern indian ocean this path is virtually identical to those obtained for the same transition from north pacific deep sea cores and partly coincides with a north atlantic record which suggests that a dipolar component may be present in the transitional field during the upper olduvai reversal a review of the recently obtained records of various transitions shows that in more than two thirds of the cases the vgp paths are similarly confined along a meridian over the americas or antipodal to them irrespective of the sampling site and of the sense of the transition although not deterministic this tendency suggests that a similar dipolar component might be present in the transitional fields of other reversals of different ages

a comparison of different magnetic methods for determining the relative grain size of magnetite in natural materials some results from lake sediments abstract a new rapid method for identifying relative grain size variations in magnetic involves the parameter anhysteretic susceptibility arm i e specific arm obtained in a 1 oe steady field which is particularly sensitive to the single domain sd and small pseudo single domain psd grains of the finer magnetite fraction a second parameter low field susceptibility is relatively more sensitive to the coarser magnetite fraction larger psd and smaller multidomain md grains we can then obtain a measure of the ratio of coarse to fine grain magnetite for large numbers of samples by plotting arversus a simple idealized model based on sized magnetite samples is proposed to explain the use of the armversus plot for detecting relative grain size changes in the magnetic content of natural materials the sediments of three lakes that contain magnetite or a similar magnetic carrier and have a wide range of values of arm and are used to test the model the model is used to interpret the magnetic variations observed and the interpretations are supported by high field hysteresis measurements of the same sediments the combination of the high field hysteresis method of day et al 1 and the arm vs method is a powerful technique allowing the rapid identification of both the relative grain size and domain state for large numbers of samples containing magnetite the armvs method should be used as an intial means of identifying distinct groups of samples the high field hysteresis method should then be applied to a few representative samples from each group to confirm the initial interpretation

a comparison of two coastal barrier jet events along the southeast alaskan coast during the sarjet field experiment abstract the southeastern alaskan regional jets experiment investigated the structures and physical processes of barrier jets along the coastal fairweather mountains near juneau alaska from 24 september to 21 october 2004 this paper compares in situ aircraft data and high resolution simulations from the first intensive observation period iop1 which featured a nearly terrain parallel barrier jet classical jet with another coastal jet event iop7 that was influenced by offshore directed gap flows at the coast hybrid jet iop1 featured southerly onshore flow preceding a landfalling trough which was blocked by the coastal terrain and accelerated down the pressure gradient to produce a 5 10 m s 1 wind enhancement in the alongshore direction in the lowest 1 km msl in contrast iop7 featured higher surface pressure and colder low level temperatures to the east inland of the study area than did iop1 which resulted in offshore directed coastal gap flow exiting cross sound below 500 m that turned a

numerical simulations of a landfalling cold front observed during coast rapid evolution and responsible mechanisms abstract this paper identifies mechanisms that led to the observed rapid evolution of a landfalling weak cold front along the steep mountainous northern california coast on 1 december 1995 this event was simulated down to 3 km horizontal grid spacing using the pennsylvania state university ncar mesoscale model version 5 mm5 the mm5 simulation reproduced the basic features such as the timing location and orientation of the cold front and associated precipitation evolution as well as the tendency for enhanced precipitation to extend 50 100 km upwind of the coastal barrier with the heaviest amounts occurring over the windward slopes 0 20 km inland locally however the model underestimated the magnitude of the prefrontal terrain enhanced flow by as much as 30 since the simulated low level static stability was weaker than observed the mm5 simulations illustrate the complex thermal wind and precipitation structures in the coastal zone upstream flow blocking by the steep coastal terrain led to

moist dynamics and orographic precipitation in northern and central california during the new year s flood of 1997 abstract the dynamics of moist orographic flows during the january 1997 floods in northern and central california are investigated using numerical simulations computed with the fifth generation pennsylvania state university national center for atmospheric research psu ncar mesoscale model mm5 early in the event 31 december 1996 1 january 1997 the low level winds offshore of california s central coast were blocked by the topography of the santa lucia range and the low level winds in the central valley were blocked by the topography of the central sierra nevada range in contrast moisture laden winds along the northern coast ranges and the northern sierra nevada flowed over topographic barriers as the core of humid air migrated to the south over 24 h the low level barrier jets weakened as the atmospheric stability decreased bringing heavy rainfall to the central and southern sierra nevada at the end of the event the heavy precipitation during this event was largely controlled by the interactio

first observations of high temperature submarine hydrothermal vents and massive anhydrite deposits off the north coast of iceland high temperature 250 c hydrothermal vents and massive anhydrite deposits have been found in a shallow water sediment filled graben near 66 36 n in the tjornes fracture zone north of iceland the site is located about 30 km offshore near the small island of grimsey the main vent field occurs at a depth of 400 m and consists of about 20 large diameter up to 10 m mounds and 1 3 m chimneys and spires of anhydrite and talc a north south alignment of the mounds over a 1 km strike length of the valley floor suggests that their distribution is controlled by a buried fault widespread shimmering water and extensive white patches of anhydrite in the sediment between the mounds indicates that the entire 1 km2 area occupied by the vents is thermally active a 2 man research submersible jago was used to map the area and to sample vent waters gases and chimneys actively boiling hydrothermal vents occur on most of the mounds and extensive two phase venting indicates that the field is underlain by a large boiling zone 200 300 m the presence of boiling fluids in shallow aquifers beneath the deposits was confirmed by sediment coring the highest temperature pore fluids were encountered in talc and anhydrite rich sedimentary layers that occur up to 7 m below the mounds baked muds underlie the talc and anhydrite layers and pyrite is common in stockwork like fractures and veins in the hydrothermally altered sediments however massive sulfides pyrite marcasite crusts were found in only one relict mound subseafloor boiling has likely affected the metal carrying capacity of the hydrothermal fluids and deposition of sulfides may be occurring at greater depth although the mounds and chimneys at grimsey resemble other deposits at sedimented ridges e g middle valley escanaba trough guaymas basin the shallow water setting and extensive boiling of the hydrothermal fluids represent a distinctive new type of seafloor hydrothermal system

fault related biogenic mounds in the ceduna sub basin australia implications for hydrocarbon migration abstract the early cenozoic in the bight basin represents a transitional period from the slow to fast oceanic crust spreading of the southern ocean between australia and antarctica this period is characterised by widespread igneous activity and the occurrence of biogenic mound complexes in the proximal part of the ceduna sub basin these mound complexes thrive on local topographic highs exploiting the shut down in siliciclastic sediment supply during the eocene new interpretation of 2d and 3d seismic data from the central ceduna sub basin shows additional undrilled paleocene eocene biogenic mound complexes they display rugose morphology progradational and aggradational internal organisation and high impedance contrast with the surrounding sediments these mounds typically show a clear relationship with underlying reactivated fault segments these faults intersect potential oil mature cretaceous source rock intervals and therefore one plausible mechanism for the development of fault related mound complexes in the central ceduna sub basin relies on natural hydrocarbon seeps along faults supplying nutrients for a benthic chemosynthetic organisms and localised biogenic mound growth the presence of a sub bottom profile anomaly overlaid by a vertical water column acoustic contact in close vicinity of a mound complex support this model the occurrence of seep related biogenic mounds would validate the presence of mature source rock s and hydrocarbon charge in the central ceduna sub basin if confirmed the biogenic mounds would imply fluid migration occurrence until at least the eocene

where did ancient carbonate mounds grow in bathyal depths or in shallow shelf waters abstract carbonate mounds are important and ubiquitous components of the sedimentary rock record throughout the phanerozoic nevertheless factors controlling their occurrence and growth remain enigmatic in particular because the depositional depths of such mounds are poorly constrained and it is assumed that fossil examples lack modern analogues factors currently used to constrain the water depth that ancient mounds grew in include water energy occurrence of specific organisms that perform photosynthesis particularly calcareous algae and distinct non biogenic components in reviewing the main criteria used to delineate water depth of formation of fossil carbonate mounds most if not all criteria traditionally used to assume shallow water settings appear to be no longer substantiated in the light of current knowledge gained from modern carbonate mounds high energy assumed to indicate shallow water conditions is ongoing in water as deep as 1000 m the occurrence of peloids and processes such as micritization is not diagnostic of water depth furthermore virtually none of the calcareous algae assumed to indicate the photic zone have a taxonomically granted affiliation over the last years research in the deep ocean in particular thanks to the deployment of new devices and techniques provided a good database revealing a wide distribution of modern carbonate mounds reviewing the characteristics of ancient carbonate mounds with emphasis on depositional settings and confronting the criteria used with current knowledge from sub recent and modern carbonate mounds we conclude that for many ancient mounds a bathyal origin is at least as likely as a shallow water origin this conclusion is well supported by the sedimentary records left by these modern mounds that are astonishingly similar to those seen in palaeozoic and mesozoic carbonate mounds

short period geomagnetic excursion recorded in pleistocene sediments of baffin bay and davis strait ten cores from the baffin bay area were sampled for paleomagnetic studies an excursion of earth9s geomagnetic field was recorded in five of the ten cores extrapolated ages assuming a nearly constant sedimentation rate place the geomagnetic excursion between 129 000 and 161 000 yr b p with a duration of 5 000 10 000 yr the oldest sediments represented in the cores are probably 400 000 yr old

role of deep sourced fluids on the initiation and growth of isolated carbonate build ups abstract the relative role of the various mechanisms responsible for the formation of isolated carbonate build ups occurring on the seafloor along continental margins is still uncertain the interpretation of an extensive seismic dataset in the central vulcan sub basin nw australia allowed to evaluate the possible role of migration and seepage of deep sourced fluids during the initial growth of isolated carbonate build ups the neogene tectonic activity along the margin generated extensional fault systems that commonly displaced the seafloor thus apparently creating a substratum to the initiation of various carbonate build ups during the pleistocene the seismic data show reflections with enhanced amplitude respect to background values which are associated with both isolated carbonate build ups and normal faults the seismic character of these reflections supports the presence of fluids that migrated within the sedimentary pile throughout the investigated area the interpreted occurrence of methane derived authigenic carbonates mdac on the seismic surface upon which the carbonate build ups lay suggests that seepage of hydrocarbons likely occurred at the time of their initial formation the fluid migration appears focused in the areas above extensional faults which breached the seals of the mesozoic reservoirs combined tectonic activity and seepage are suggested to support the initial growth of the carbonate build ups various smaller buried carbonate build ups developed contemporaneously to those on the present day seafloor in sites that lack evidence of past hydrocarbon seepage their shorter life compared to those on the present day seafloor suggests their inability to keep up with the frequent relative sea level variations during the quaternary and the importance of deep sourced fluids for the carbonate build ups growth in the central vulcan sub basin the initiation of the numerous carbonate build ups documented along continental margins worldwide must be explained considering the complex and dynamic interplay of all factors potentially involved such as geological and oceanographic settings and an active petroleum system in particular the migration and seepage of deep sourced fluid can have an important role in controlling the genesis and growth of isolated carbonate build ups

miocene shallow marine cold seep carbonate in fold and thrust western foothills sw taiwan a mound shaped authigenic carbonate buildup 50 m wide and 5 m high occurred in the middle part of the late miocene shallow marine succession the hunghuatzu formation exposed along the nantzuhsien river sw taiwan the carbonate concretions are classified into four types based on morphology which appeared to develop in upward sequence with vague boundaries 1 flat pipe shaped nodules highly dolomitic small pipes or nodules subparallel to the host strata 2 bulb shaped nodules discrete or combined small mesoclots with subspherical to irregular shapes 3 mushroom shaped concretions large mushroom like or irregular shaped blocks with chimney or vent structures and 4 carbonated layers with sedimentary structures these concretions are mainly composed of dolomite micrites quartz feldspar muscovite and clay minerals ubiquitously interweaved with blackish brown colored low magnesium calcite lmc veins low delta c 13 vpdb values 51 8 parts per thousand to 29 8 parts per thousand of all types of the carbonates reveal that the carbonates were mainly derived from anaerobic oxidation of hydrocarbons many samples are also o 18 depleted delta o 18 vpdb 11 5 parts per thousand to 1 00 parts per thousand due to the mixture with isotopically light lmc veins likely precipitated from meteoric waters there are numerous chemosymbiotic bivalve fossils genus monitilora diameter 3 4 cm in growth position just above the carbonate buildup according to the geological and isotopic signatures the hunghuatzu carbonates are related to a cold seep pseudobioherm which formed in a very shallow marine environment like tidal flat in a passive margin setting exposures of the hunghuatzu pseudobioherm may provide clues for tracking and comparing the evolution history of gas reservoir systems and hints of active tectonics of the sw taiwan region c 2012 elsevier ltd all rights reserved

fault associated seabed mounds carbonate knolls off western ireland and north west australia abstract groups of seabed mounds suspected to be modern carbonate knolls or bioherms have been located on reflection seismic data in the porcupine basin off western ireland and in the vulcan sub basin off north west australia the size of these mounds is impressive often being over 1 km across and over 100 m high in the porcupine basin they occur in water depths of 650 1000 m whereas in the vulcan sub basin they occur in water depths of 200 350 m shallow seabed coring in the porcupine basin has provided data on the age lithological composition and hydrocarbon concentrations in the upper 3 m layer of sediment both on and off the mounds in both basins the mounds occur close to faults which may provide conduits for upward migrating hydrocarbons the seepage of hydrocarbons is suspected to have caused local eutrophication or fertilization by providing nutrients to bacteria which in turn are part of the food chain for higher organisms the dominant organism in the porcupine basin examples appears to be the deep water coral lophelia sp whereas in the vulcan sub basin the mounds appear to be halimeda dominated

do carbonate reefs form due to fluid seepage buried carbonate reefs are favoured hydrocarbon prospecting targets mainly due to their high porosity and potential for containing large quantities of petroleum the question of the true relationship between reef structure and the internally trapped fluids hydrocarbons is here raised as one of cause and effect in other words which came first the hydrocarbons or the carbonate reef itself modern bioherms and seabed carbonate reefs in amongst other locations the north sea and the gulf of mexico are shown to form in close association with active hydrocarbon seepages mainly based on results from ecological studies at deep ocean vent communities a new model for carbonate reef formation is promoted that such reefs form at locations containing high concentrations of bacteria and other microorganisms suspended in the water column as a result of seeping fluids solutions and gases that provide some of the energy basis and carbon source for ecosystems independently of photosynthesis therefore on burial and effective sealing capping these carbonate reefs become hydrocarbon reservoirs trapping and accumulating the very minerals on which they in the first place were dependent

anatomy and origin of carbonate structures in a miocene cold seep field miocene calcite concretions resembling modern carbonate structures that form at cold seeps are present in fractured opal ct porcelanites that are interbedded with mudstones in coastal cliffs at santa cruz california the morphologies of the carbonate structures differ markedly from conventional concretions and are spatially aligned with orthogonal joints in the porcelanites the structures contain tubular holes that are identical to fluid and gas conduits in modern carbonate seep structures the orientations of these tubes suggest that fluid and gas flow was both vertical and horizontal the latter along extensional joints that formed preferentially in the brittle silica rich layers that had enhanced bedding parallel permeability petrographic and isotopic characteristics of the carbonate structures indicate that calcite precipitation occurred in a shallow subseafloor environment in either the zone of microbial sulfate reduction or of methanogenesis prior to or possibly simultaneously with the silica phase transformation of opal a in diatom shells to opal ct

airborne doppler observations of a cold front in the vicinity of vancouver island abstract this study uses airborne doppler radar and flight level measurements from the coastal observations and simulations with topography experiment to examine the detailed mesoscale structure of an oceanic cold front upstream of vancouver island on 13 december 1993 these aircraft observations show that there were dramatic differences in frontal structure and movement between nearshore and offshore regions presumably due to the effects of blocking by the terrain the aircraft observations are considered in two parts since the behavior of the front evolved over the flight period during the early and middle portion of the flight the low level flow east of the front was out of the south southeast in the nearshore region rather than southerly as found farther offshore the nearshore segment of the front was oriented south north and appeared to be stationary the zone of orographic influence was found to extend to a region 20 km offshore and confined primarily to the lowest 1 5 km msl in distinct c

formation of the convective lines off the mountainous coast of southeastern taiwan a case study of 3 january 2004 abstract convective lines frequently occurring off the mountainous coast of southeastern taiwan under weakly synoptically forced weather conditions are one of the most well known mesoscale phenomena in taiwan these lines usually develop close to the coast but frequently can also be observed well offshore while nearshore lines are better understood the formative processes of the offshore lines remain unclear the main objective of this study is to use various available observations e g doppler radar surface and sounding observations quikscat and ncep data collected over southeastern taiwan to investigate a specially chosen case on 3 january 2004 in an attempt to identify possible mechanisms leading to the formation of the offshore lines the studied line was formed 50 60 km away from the southeastern coast of taiwan and oriented south southwest to north northeast and approximately parallel to the coast detailed analyses of the event indicated that the formation of the line did not appear direc

methods for identification of isolated carbonate buildups from seismic reflection data isolated carbonate buildups icbs are commonly attractive exploration targets however identifying icbs based only on seismic data can be difficult for a variety of reasons these include poor quality two dimensional data and a basic similarity between icbs and other features such as volcanoes erosional remnants and tilted fault blocks to address these difficulties and develop reliable methods to identify icbs 234 seismic images were analyzed the images included proven icbs and other features such as folds volcanoes and basement highs which may appear similar to icbs when imaged in seismic data from this analysis 18 identification criteria were derived to distinguish icbs from non icb features these criteria can be grouped into four categories regional constraints analysis of basic seismic geometries analysis of geophysical details and finer scale seismic geometries systematically assessing the criteria is useful because it requires critical evaluation of the evidence present in the available data working from the large scale regional geology to the fine details of seismic response it is also useful to summarize the criteria as a numerical score to facilitate comparison between different examples and different classes of icbs and non icbs our analysis of scores of different classes of features suggests that the criteria do have some discriminatory power but significant challenges remain

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

kinematic and thermodynamic structures of sierra barrier jets and overrunning atmospheric rivers during a landfalling winter storm in northern california abstractthis study characterizes kinematic and thermodynamic structures of sierra barrier jets sbjs atmospheric rivers ars and their interaction over the period 14 16 february 2011 when a winter storm made landfall in northern california a suite of scanning and profiling doppler radars rawinsondes and gps receivers is used to document these structures across the central valley and up the western sierra slope to the crest along an 200 km segment of the sierra the winter storm is grouped into two episodes each having an ar that made landfall low level winds in the sbj observed during episode 1 were southeasterly and embedded in a stably stratified air mass along barrier wind speeds u340 reached maximum values of 25 30 m s 1 as low as 0 2 km msl over the central valley and as high as 1 5 km msl over the western sierra slope southwesterly winds associated with the ar overlaid the sbj along an interface that sloped upward from southwest to northeast with a southwestern extent at the western

geometric and depositional responses of carbonate build ups to miocene sea level and regional tectonics offshore northwest australia abstract the geometric and depositional responses of isolated carbonate build ups to miocene sea level change and regional tectonics are investigated using 3d seismic and borehole data from the browse basin north west australia combined with outcrop information from the cariatiz reef southeast spain the interpreted seismic volume documents five 5 miocene sequence boundaries and five 5 main seismic facies seismic attribute analyses proved to be a highly effective tool for interpreting carbonate facies but when compared with outcrop information from southeast spain attribute data are limited to features larger than 16 4 m vertically and 18 75 m horizontally estimations of reservoir potential are thus significantly underestimated when only based on the interpretation of seismic data as a corollary of the structural analysis in this work growth patterns suggest messinian structural partitioning across the browse basin with deformation associated with plate collision focused on preferentially oriented faults i e only influencing carbonate build up evolution at a local scale

investigation of orographic precipitation over an isolated three dimensional complex topography with a dense gauge network radar observations and upslope model abstractthis study uses a dense rain gauge network radar observations and an upslope model to document the detailed aspects of precipitation over da tun mountain dt of northern taiwan under pre

an observational and numerical study of an orographically trapped wind reversal along the west coast of the united states abstract observational analyses and a high resolution simulation using the pennsylvania state university ncar mesoscale model version 5 mm5 were used to describe the coastally trapped wind reversal of 19 21 july 1994 major findings include the following the event was initiated and controlled by changes in the synoptic scale flow and particularly by the development of offshore flow over the coastal terrain of oregon although synoptic control was dominant blocking of the inversion capped marine layer and mesoscale coastal pressure ridging were important components of the event the synoptic evolution associated with the trapped reversal was characterized by a shift from climatological near zonal 500 mb flow to high amplitude upper level ridging over the eastern pacific as this upper ridge moved northeastward the 850 mb flow over oregon became northeasterly and then southeasterly and 850 mb heights fell over western oregon the combination of falling heights aloft and increasing low level offshore

controls on the distribution and growth of isolated carbonate build ups in the timor sea nw australia during the quaternary abstract isolated carbonate build ups icbs represent attractive hydrocarbon exploration targets they are often seen as long term transgressive features but their distribution within basins and growth history can be difficult to predict as they respond to the interplay between various tectonic eustatic and oceanographic parameters here we use a 3d seismic megasurvey 18 000 km2 combined with well data to understand the timing and mechanisms of formation of tropical quaternary icbs in nw australia at present the icbs are typically 1 30 km wide and form clusters of 150 build ups developing 2 85 km from the edge of a 650 km wide continental shelf our results demonstrate that the structural evolution of the margin had a major impact on the distribution of the icbs main period of fault activity commenced during the latest miocene early pliocene corresponding to the initial collision of the australian plate with banda arc fault activity increased from late pliocene and peaked during the early pleistocene it was associated with flexural reactivation of structural highs uplift and lows subsidence along the shelf margin seismic evidence of moat channel and drift deposits suggest that contour current activity intensified during the late early pleistocene ca 1 ma bp despite potentially good conditions for carbonate production basement highs and warm water ocean currents icbs did not form until the mid pleistocene ca 0 582 0 8 ma bp this age corresponds to the onset of major sea level fluctuations associated with repeated high amplitude 120 m rapid deglacial rises and slow falls thus we infer that the nw australia icbs formed due to 1 structural shaping of the margin 2 oceanographic changes and most importantly 3 onset of repeated high amplitude transgressions reactivating the carbonate production along isolated highs following 4th 5th order lowstand exposures and allowing catching up carbonate morphologies to develop

late quaternary calcareous nannofossil biozonation chronology and palaeo oceanography in areas north of the faeroe iceland ridge abstract the stratigraphic distribution of late quaternary calcareous nannofossils from the european arctic ocean the fram strait and the norwegian and greenland seas are summarised in a biozonation scheme the nannofossil events are directly correlated to oxygen isotope stratigraphy leading to an absolute chronology comprising approximately the last 500 ka the zones are defined by the qualitative and quantitative content of calcareous nannofossils zones n g 2 4 6 8 and 10 comprise intervals mainly barren of nannofossils zone n g 1 is characterised by high abundances of coccolithus pelagicus and emiliania huxleyi zone n g 3 is recognised by dominant gephyrocapsa muellerae and common e huxleyi zone n g 5 is characterised by dominant g aperta n g 7 by dominant g muellerae n g 9 by common g muellerae g aperta and g caribbeanica and zone n g 11 is recognised by dominant g caribbeanica and rare pseudoemiliania lacunosa intervals in which nannofossils occur in high abundances reflect comparatively warmer periods and influences of north atlantic surface water strong inflows of north atlantic water have occurred several times during the last 500 ka in oxygen isotope stage 1 the last 8 ka and in oxygen isotope stages 5 11 12 and 13 north atlantic surface water penetrated into the central parts of the norwegian and greenland seas also during oxygen isotope stage 9 nannofossil barren intervals are mainly formed during time periods with a year round ice cover

the role of offshore convergence on coastal rainfall during tamex iop 3 abstract the role of offshore convergence on the coastal rainfall maximum along the northwestern coast of taiwan is analyzed based on tamex taiwan area mesoscale experiment data and numerical experiments using the fifth generation pennsylvania state university national center for atmospheric research psu ncar mesoscale model mm5 from a case study during tamex iop 3 moderate rainfalls 40 mm h 1 are observed along the northwestern coast of taiwan associated with the arrival of three rainbands in succession during 1000 1600 lst these rainbands form over the taiwan strait with northeast southwest or north south orientation they intensify off the northwestern coast there is a tendency for the most intense echoes to align in a northeast southwest orientation off the northwestern coast an orographically enhanced convergence zone with a northeast southwest orientation occurs in the area where the deflected southerly flow converges with the prevailing southwesterly flow that is modified by the storm

numerical simulations of the barrier jet over northwestern taiwan during the mei yu season orographic effects on the airflow over taiwan under the prevailing southwesterly monsoon flow are studied using the fifth generation pennsylvania state university national center for atmospheric research psu ncar mesoscale model mm5 in particular the orographically induced low level strong winds along the northwestern coast of taiwan are simulated in the absence of radiative forcing thermal forcing from the surface and synoptic forcing the momentum balance for the low level strong winds along the northwest coast of taiwan shows that above the mixed layer the alongshore force balance is dominated by the inertial advection term and the pressure gradient force term the significant lagrangian flow acceleration of the northern branch of the deflected airflow along the northwest coast is mainly related to the pressure gradient force as the airflow moves down the orographically induced pressure ridge along the windward coast even though the alongshore pressure gradient force along the northwest coast is largest at the surface the observed and simulated wind profiles show that the wind speed maximum in the vertical of the barrier jet occurs at a height of 800 m primarily due to frictional retardation in the lowest levels within the well mixed layer the alongshore force balance is a threeway balance between inertial advection pressure gradient force and frictional force normal to the northwest coast the force balance is approximately geostrophic in addition the location and the strength of the orographically induced low level strong winds along the northwest coast of taiwan also depend on the impinging angle and the wind speed of the prevailing winds

paleo oceanographic and tectonic settings of early miocene reefs and associated carbonates of offshore southeast asia the late oligocene to early middle miocene was a period of widespread reef and associated carbonate deposition over a wide latitudinal range in the offshore region of southeast asia a generally rising eustatic sea level during this period allowed the accumulation of thick reefal units an expansion of the coral algal regional facies belt north to japan and south to new zealand occurred during the early miocene as the result of a reduced oceanic latitudinal temperature gradient an episode of enhanced organic carbon burial is reflected in a positive dgr13c excursion from 17 5 to 13 5 ma increasing paleo oceanographic equability may have resulted in reduced ocean circulation with the resultant development of an expanded oxygen minimum zone marine oil prone or anic carbon was deposited in silled anoxic basins both bounded by and within island arc systems a combination of tectonic and paleo oceanographic factors therefore created conditions that favored contemporaneous deposition of organic carbon rich source beds and reef reservoirs during the latest early to early middle miocene paleogeographic and facies reconstructions for an 18 m y interval indicate that deposition occurred in three tectonic settings 1 passive continental margins 2 convergent plate boundaries and 3 obliquely convergent plate boundaries in all these settings the vertical motion histories of fault bounded blocks and of larger tectonic elements within which they are contained directly controlled the geographical distribution of carbonate buildups their scal and morphology duration diagenesis and relationship to siliciclastics

evidence for a new geomagnetic reversal from lava flows in idaho discussion of short polarity reversals in the brunhes and late matuyama polarity chrons k ar ages and paleomagnetic data for basalt samples from a new core hole site e at the idaho national engineering laboratory inel indicate that the age of the reversed polarity event recorded in snake river plain lavas is older than 465 50 ka 1000 years before present reported previously by champion et al 1981 nine basalt flows eight with normal polarity and one with reversed polarity were recognized in the site e core hole the flows above and below the reversed flow have ages of 491 80 ka and 580 93 ka respectively the inclination of the paleomagnetic field direction of the reversed flow at site e agrees with the inclination of reversed flows elsewhere at inel which have an age of 565 14 ka these reversed flows were previously thought to be correlative with the emperor event we suggest that this polarity event is an older event which we name the big lost reversed polarity subchronozone and subchron a review of data documenting short reversal records from volcanic and sedimentary rocks shows that there is evidence for eight polarity subchrons in the brunhes and two besides the jaramillo in the late matuyama these 10 short subchrons begin to indicate the many short events that cox 1968 hypothesized must exist if polarity interval lengths have a poisson distribution these events are true subchrons not excursions and may or may not have low associated paleointensities although low field strengths might explain why the reversal process aborts the mean sustained polarity interval length since late matuyama chron time is 90 000 years the similarity of this number with the 105 year period of the earth s orbital eccentricity suggests anew that linkage between geomagnetic paleoclimatic and possible underlying earth orbital parameters should be evaluated

the kinematic structure of a wasatch mountain winter storm during ipex iop3 the influence of orographic circulations on the precipitation structure of a wasatch mountain winter storm is examined using observations collected during the third intensive observing period iop3 of the intermountain precipitation experiment ipex the event featured the passage of a midlevel 700 550 hpa trough followed 3 h later by a surface trough prior to and during the midlevel trough passage large scale southwesterly flow impinged on the wasatch mountains low level confluence was observed between this southwesterly flow and along barrier southerly flow within 20 40 km of the wasatch mountains this confluence zone which moved toward the wasatch mountains during and following the passage of the midlevel trough was accompanied by low level convergence and precipitation enhancement over the upstream lowlands dual doppler analysis revealed the presence of a shallow along barrier jet near the base of the wasatch mountains that was surmounted by southwesterly cross barrier flow at mid and uppermountain levels this cross barrier flow produced strong 1 2 m s 1 ascent as it interacted with the steep windward slopes of the wasatch mountains where precipitation was roughly double that observed in the lowlands upstream flow deflection and splitting were also observed near the highest terrain features a narrow region of strong subsidence which at times exceede d2ms 1 was found to the lee of the wasatch and based on radar imagery appeared to modulate hydrometeor spillover aloft processes contributing to the evolution of the near barrier flow field including topographic blocking diabatic effects and surface friction contrasts are discussed

borehole observations of fluid flow from south chamorro seamount an active serpentinite mud volcano in the mariana forearc abstract a sealed borehole observatory cork was deployed on south chamorro seamount an active serpentinite mud volcano in the mariana forearc to explore subduction related processes on a non accretionary convergent plate margin formation fluid was overpressured relative to ambient hydrostatic conditions fluid flowed from the borehole at 0 2 l s when the observatory was opened to recover instruments 2 yr after it was installed the chemical composition of the formation fluid is similar to that extrapolated from trends in pore water data collected during ocean drilling program leg 195 when the observatory was established reduced sulfur is present in this highly alkaline ph 12 4 formation fluid indicative of microbial activity at or below the depth of the screened casing 149 202 m below the seafloor discharge from the open borehole continued for 37 days until the observatory was resealed this discharge requires significant permeability at depth 6 10 14 m2 zones of high permeability may be associated with the formation of headwall scarps consistent with numerous slumps on the southeastern flank of the seamount and likely shape a geochemical environment suitable for an active microbial community

three dimensional idealized simulations of barrier jets along the southeast coast of alaska abstract three dimensional idealized simulations using the fifth generation pennsylvania state university ncar mesoscale model mm5 down to 6 km grid spacing were performed in order to understand how different ambient conditions wind speed and direction stability and inland cold pool and terrain characteristics impact barrier jets along the southeastern alaskan coast the broad inland terrain of western north america is important in alaskan jet development since it rotates the impinging flow cyclonically more coast parallel well upstream of the coast thus favoring more low level flow blocking while also adding momentum and width to the barrier jet near the steep coastal terrain the largest wind speed enhancement factor 1 9 2 0 in the terrain parallel direction relative to the ambient onshore directed wind speed occurs at relatively low froude numbers fr 0 3 0 4 these low froude numbers are associated with 10 15 m s 1 ambient wind speeds and wind directions orientated 30 45 from terra

retrieved thermodynamic structure of a subtropical orographically influenced quasi stationary convective line airborne doppler radar and flight level measurements were used to document the three dimensional thermodynamic structure of a convective line that developed off the southeastern coast of taiwan on 16 june 1987 during the taiwan area mesoscale experiment during the period of aircraft observation the convective line appeared to be quasi stationary in a region 90 km away from the coast calculations of perturbation pressure and buoyancy retrieved from the doppler radar derived wind fields show that a high pressure perturbation associated with negative buoyancy existed in the region of heavy precipitation in the lowest level in low levels an elongated zone of low pressure was documented along the line which was closely related to the distributions of buoyancy these retrieved features are basically consistent with those calculated from in situ observations in mid to upper levels the high low pressure perturbation lay around the updraft cores on the upshear downshear of environmental shear the quantitative diagnosis for the perturbation pressure indicates that the positive buoyancy associated with the in cloud latent heat release as well as evaporative cooling occurring near cloud base and subcloud regions is crucial to determine the low level perturbation pressure distributions however dynamic forcing contributing to the pressure perturbation cannot be ignored in middle levels because of updraft shear interaction due to the presence of pronounced cross line wind shear and corresponding updrafts reaching maximum values near midtroposphere in distinct contrast to squall lines which are rapidly moving the near surface temperature gradient across this quasi stationary line was very weak and at low levels no gust front rear inflow or dynamically induced high pressure was evident near the leading edge of the line analyses presented here suggest that the persistent stationary convergence in association with the deceleration of low level southeasterly flow as it approached the nearshore blocked flow played an important role in maintaining and organizing the deep convection in this case

stable isotope stratigraphy of the arctic ocean fram strait to central arctic abstract a comparison of stable isotope and textural records of sediment cores from the fram strait and central arctic ocean to isotopic records from low latitude oceans indicates that the arctic mediterranean responded dynamically to climatic change during the pleistocene core mg 123 from the fram strait shows at least four significant low 18 o intervals 5 high 13 c intervals and five intervals with a low amount of coarse sediment the association of high 18 o values with coarse sediment intervals indicates increased glacial ice in the fram strait during glacial phases of the climate cycle peaks within the low 18 o intervals increase in magnitude from oldest to youngest suggesting that glacial interglacial transitions are pulsed the magnitude of the different low 18 o intervals increases from oldest to youngest this is interpreted to indicate that there has been a progressive intensification of the oceanographic response to glacial interglacial transitions in the fram strait during the past 524 ky time series spectral analysis suggests an age of approximately 524 ky for the oldest sediment in core mg 123 yielding an average sedimentation rate of approximately 1 66 cm 1000 yr stable isotope records from the central arctic ocean indicate that sedimentation rates are on the order of 1 3 mm 1000 yr the isotope records support the established central arctic ocean lithostratigraphy coarse sediment deposition in the central arctic is not as clearly related to glacial conditions as it is in the fram strait the oxygen isotope range of central arctic ocean records is accentuated relative to the global ice volume signal recorded from lower latitude cores this may be caused by variations in salinity temperature and thickness of the arctic ocean s low salinity surface layer oceanographic responses to climatic change recorded in the fram strait are also recorded in the central arctic ocean but with decreased resolution due to the magnitude of difference in the sedimentation rates between the two areas

airborne doppler observations of a landfalling cold front upstream of steep coastal orography abstract this study uses airborne doppler radar observations to describe the mesoscale structure and evolution of a cold frontal system as it made landfall on the mountainous coast of oregon and northern california on 1 december 1995 during the coastal observations and simulations with topography experiment this section of coastline constitutes a steep approximately two dimensional north south oriented orographic barrier the front exhibited a northeast southwest orientation and thus intersected the axis of high terrain at an acute angle the along barrier pressure gradient and low level winds increased with time along the coastal zone and reached a maximum as the front made landfall stably stratified prefrontal flow was strongly blocked by the orography resulting in a confluent transition from pervasive southwesterly winds offshore to a narrow zone of accelerated south southwesterly flow near the coast where wind speeds approached 30 m s 1 at a height of 750 m above mean sea level postfrontal flow

seismic geomorphology and evolution of early mid miocene isolated carbonate build ups in the timor sea north west shelf of australia abstract analysis of extensive 2d and 3d seismic data reveals the presence of about sixty isolated carbonate build ups icbs of early mid miocene age spreading over a wide area of the northwestern bonaparte basin individual build ups are 100 m thick with an average diameter of 3 km integration of full volume 3d seismic attribute analysis with extensive biostratigraphic and lithological data from exploration wells allows examining the evolution of icbs and their associated morphologies at high resolution the development of icbs took place above a seismically flat surface the stratigraphic architecture of the build ups typically consists of 1 mid burdigalian initiation tf1 cn2 2 lateral expansion during the late burdigalian cn3 and 3 backstepping and drowning during the langhian tf2 cn4 this is followed by sub aerial exposure that probably corresponds to a major sea level fall during the serravallian only small patch reefs pinnacles developed afterwards during the late miocene the observed growth phases of the icbs correlate with global sea level fluctuations and major changes in global climate and oceanography the role of local tectonics in the initiation and demise of these build ups appears as minimal growth of the northwestern bonaparte basin icbs is synchronous with the establishment of tropical carbonate factories elsewhere along the australia s north west shelf that suggest an acme of reef development during the early to middle miocene

pinnacle features at the base of isolated carbonate buildups marking point sources of fluid offshore northwest australia we investigated pinnacle features at the base of late oligocene miocene isolated carbonate buildups using three dimensional seismic and borehole data from the browse basin northwest australia brightened seismic reflections dim spots and other evidence of fluid accumulation occur below most pinnacle features an important observation is that all pinnacles generated topography on successive late oligocene miocene paleoseafloors therefore forming preferential zones for the settlement of reef building organisms by raising the paleo seafloor into the photic zone their height ranges from 31 m to 174 m for a volume varying from 33 km3 to 11 105 km3 most of the pinnacles however are less than 2000 km3 in volume and present heights of 61 80 m as a result of this work pinnacles are explained as the first patch reefs formed in association with mud volcanoes or methanogenic carbonates and they are considered as precluding the growth of the larger isolated carbonate buildups we postulate that pinnacle features above fluidflow conduits demonstrate a valid seep reef relationship and we propose them to be refined diagnostic features for understanding fluid flow through geological time

distribution stratigraphy petrochemistry and palaeomagnetism of the late pleistocene old crow tephra in alaska and the yukon revision accepted january l i 1985 the late quaternary old crow tephra is a two pyroxene calc alkaline dacite whose known areal extent is broadly delimited by a triangle with apices at the seward peninsula the wrangell mountains and the old crow basin in the northern yukon everywhere the tephra is fine grained mdu 5 33 2 0 32 and moderately to poorly sorted 6u 1 33 0 29 samples from the extremities of the fall out zone have similarity coefficients of 0 95 a palaeomagnetic excursion is recorded in sediments just below old crow tephra in the fairbanks area and at imuruk lake on the seward peninsula a short full reversal of the magnetic field has been preserved at the corresponding stratigraphic level near old crow in the northern yukon chronological controls based on i4c and fission track dates and sedimentation rates show that these palaeornagnetic features are almost certainly partial records of the complex geomagnetic blake event which occurred 100 120 ka ago new petrochemical data demonstrate that the source of old crow tephra is in the eastern aleutian arc

effect of the andes cordillera on precipitation from a midlatitude cold front the effects of the andes cordillera the major mountain range in south america on precipitation patterns of baroclinic systems approaching from the southeast pacific remain largely unstudied this study focuses on a case in late may 2008 when an upper level trough and surface cold front produced widespread precipitation in central chile the primary goal was to analyze the physical mechanisms responsible for the structure and evolution of the precipitation weather research and forecasting wrf model simulations indicate that as an upper level trough approached central chile midtropospheric flow below 700 hpa was blocked by the high topography and deflected poleward in the form of a barrier jet this northerly jet had wind maxima in excess of 15 m s 21 was centered around 925 hpa and extended westward 200 km from the mountains it intersected the cold front which approached from the south near the coast thereby increasing convergence along the frontal surface slowing its equatorward progress and enhancing rainfall over central chile another separate region of heavy precipitation formed over the upwind slopes of the cordillera a trajectory analysis confirmed that the barrier jet moved low level parcels from their origin in the moist southeast pacific boundary layer to the coast when model topography was reduced to twenty percent of its original height the cold front advanced more rapidly to the northeast generated less precipitation in central chile between 338 and 368s and produced minimal orographic precipitation on the upwind andean slopes based on these findings the high topography appears responsible for not only orographic precipitation but also for substantially increasing precipitation totals over the central coast and valley

idealized three dimensional modeling of seasonal variation in the alaska coastal current 1 seasonal variation of the buoyancy and downwelling wind forced alaska coastal current acc and the fate of freshwater contained in it is considered using idealized analytical and numerical models of the acc formed from a half line source of buoyant inflow the coastal current initially develops two dimensionally but becomes three dimensional from a balance between coastal influx of buoyancy and its downstream transport which leads to a coastal current depth limit hmax 1 2 where x is along shelf distance q is the line source strength for unit length f is the coriolis frequency and g is the reduced gravity of the buoyant inflow this limit is unchanged under downwelling wind stress and is reached on timescales of less than 1 month for the acc the coastal current width is roughly constant in x and increases in time at the same rate as the two dimensional solution imposition of a downwelling wind stress results in an approximate balance among wind stress and along and cross shelf momentum advection so that the current width is reduced to ywind ld 1 2 where ld is the rossby radius of deformation is the wind stress and 0 is a reference density waves eddying motions eventually grow in the half line source coastal current with wavelengths proportional to the coastal current width and with a downstream phase speed slower than the maximum current speed these features cause an offshore flux of buoyant water a broader coastal current and further accumulation of buoyancy on the shelf increasing downwelling wind stress reduces the effects of the instabilities continual accumulation of buoyancy on the shelf occurs during all model runs but is nearly absent under maximum winter downwelling wind stress it is suggested that freshwater accumulation on the shelf during spring summer and fall may be largely lost downstream during winter

fluid sources and stable isotope signatures in authigenic carbonates from the northern apennines italy abstract authigenic carbonates are frequently associated with methane cold seep systems which extensively occur in various geologic settings worldwide of interest is the relation between the fluids involved in their formation and the isotopic signals recorded in the carbonate cements along the northern apennines foothills italy hydrocarbons and connate waters still seeping nowadays are believed to be the primary sources for the formation of fossil authigenic carbonate found in plio pleistocene marine sediments four selected outcrops of dolomitic authigenic carbonates were analysed to compare signature of seeping fluids with fractionation of stable carbon and oxygen isotopes recorded in the carbonate along the foothills deep methane rich fluids spontaneously rise to the surface through mud volcanoes or are exploited in wells drilled nearby to the fossil plio pleistocene authigenic carbonates the plumbing system providing fluids to present day cold seeps was structurally achieved in late miocene and plio pleistocene 13 c values of methane which vary from 51 9 to 43 0 vpdb indicate that gas composition from the deep hydrocarbon reservoirs is relatively uniform along the foothills on the contrary 13 c in fossil authigenic carbonates strongly varies among different areas and also within the same outcrop the different carbon sources that fed the investigated carbonates were identified and include thermogenic methane from the deep miocene reservoirs 13 c enriched co 2 derived from secondary methanogenesis and microbial methane from pliocene successions buried in the po plain the 13 c variability documented among samples from a single outcrop testifies that the authigenic carbonates might represent a record of varying biogeochemical processes in the hydrocarbon reservoirs the sources of stable oxygen isotopes in authigenic carbonates are often ascribed to marine water oxygen isotopic fractionation in the dolomite cements indicates that marine pore water couldn t be the sole source of oxygen 18 o values provide a preliminary evidence that connate waters had a role in the carbonates precipitation the concomitant occurrence of active cold seepages and fossil record of former plumbing systems suggests that generation and migration of hydrocarbons are long lasting and very effective processes along the northern apennines foothills

early stage orogenesis in the timor sea region nw australia neogene collision between the australian eurasia and pacific plates was coeval with the growth of major depocentres in the timor sea seismic cross sections across these troughs identify a characteristic architecture all three lie inboard of diffuse horst like structural highs and all mimic older depressions in the top permian and upper jurassic surfaces distortion of pre tectonic aptian oligo miocene sequences indicates apparent trough subsidence was coupled to uplift of outboard highs rudimentary cross section restoration identifies negligible strike normal length change we interpret apparent neogene subsidence to reflect amplification of basement topography this was not accommodated by discrete structural inversion rather landward propagation of contractional strain caused continuous vertical amplification of basement topography at shallow levels normal faulting accommodated flexure and thin skinned collapse of detached sedimentary cover permitting it to shed away from structural highs and pond in adjacent troughs we infer that shortening of the north west shelf accommodated oblique convergence between australia and the eurasia pacific arc and speculate that the transcurrent component of this deformation was partitioned well outboard neogene modification is interpreted to reflect the earliest stages of collisional orogenesis

climatology of barrier jets along the alaskan coast part ii large scale and sounding composites abstract this paper investigates the large scale flow and thermodynamic structures associated with barrier jets along the alaskan coast using the national centers for environmental prediction ncep reanalysis as well as the average wind moisture and thermodynamic soundings at yakutat alaska yak and whitehorse yukon territory canada yxy large scale and sounding composites are constructed for all barrier jets objectively identified around yak using synthetic aperture radar sar imagery during the cool and warm seasons of 1998 2003 during the cool season the jet events are separated into those with sharp upstream wind gradients shock jets highly variable gustlike surface winds variable jets and the other jet events other jets those cool season barrier jets without shock or variable characteristics are associated with an anomalously deep upper level trough approaching the gulf of alaska and an anomalous ridge over western canada and interior alaska the associated surface cyclone a

formation and maintenance of a long lived taiwan rainband during 1 3 march 2003 abstracttaiwan rainbands trs defined here as convective lines which form off the mountainous eastern coast of taiwan under weakly synoptically forced weather conditions are a well known mesoscale phenomenon but their formative processes remain the subject of debate this study uses surface and radar observations within the coastal zone of eastern taiwan and ncep reanalysis data to document a long lived tr with a lifetime of 36 h during 1 3 march 2003 to advance the current general understanding of mechanisms responsible for the tr s formation and maintenance detailed analyses indicate that the rainband was initiated by convergence that was produced as low level environmental northeasterly easterly onshore flow encountered topographically blocked northerlies that developed nearshore the northerly blocked flow was observed to weaken and subsequently dissipate because of changing synoptic pressure patterns that caused prevailing southeasterlies southerlies at low levels however colder nearshore ai

a possible lacustrine paleomagnetic record of the blake episode from pringle falls oregon u s a abstract we have studied a high resolution paleomagnetic record of a magnetic polarity episode recovered from a 20 m section of diatomaceous lacustrine sediments from pringle falls near la pine oregon 43 7 n 238 6 e a total of 474 samples 982 specimens were collected at about 5 cm intervals from the 20 m section the age of this record is at present constrained between 0 6 ma and 18 000 yr based upon a pollen date from the older part of the lakebed sequence and the age of the younger glacial deposits that overlie the lakebeds the characteristic magnetization of the samples was determined by alternating field af demagnetization to 15 mt the average normal polarity stable declination and inclination of the non magnetic polarity episode sampled section 61 95 2 6 is statistically equivalent to that expected at this site for a geocentric axial dipole 62 the record provides a virtual geomagnetic pole vgp path that identifies a well defined clockwise ne sw loop with a radius of 60 followed by a second younger feature that traces out a counter clockwise loop 15 in radius residing in the ne quadrant and characterized by low latitudes interpretation of the natural remanent magnetization anhysteretic remanent magnetization nrm arm ratios for the samples indicates that the field intensity may have fallen and then increased above the average dipole field intensity the low intensity interval ends before the onset of the polarity episode as defined by directions and may suggest that the episode is a result of an unstable regeneration of the field after a significant lowering of overall field intensity these two characteristic features are similar to the two features present in the blake geomagnetic polarity episode at 114 000 and 105 000 yr bp observed in different parts of the world

damaging southerly winds caused by barrier jets in the cook strait and wellington region of new zealand abstractstrong southerly winds regularly occur in the cook strait region of new zealand occasionally these winds are strong enough to cause severe damage to property and threaten human life one example of a storm containing such winds is the wellington storm which occurred on 20 june 2013 for this case wind speeds in cook strait were stronger than those observed or forecast elsewhere in the storm even though wind speeds of this intensity are rare storms affecting new zealand with central pressures equal to the wellington storm 976 hpa are not uncommon numerical experiments have been carried out to investigate the possible reasons for the exceptional damaging southerly winds dsws occurring in this storm analyses of the simulations showed that dsws in cook strait for this event were actually barrier jets not gap winds as they appeared the strength of barrier jets in cook strait is sensitive to the precise location of the storm center this explains the uncommon occurrence of dsws in cook

evaluating hydrocarbon trap integrity during fault reactivation using geomechanical three dimensional modeling an example from the timor sea australia three dimensional 3 d coupled deformation and fluid flow numerical modeling are used to simulate the response of a relatively complex set of trap bounding faults to extensional reactivation and to investigate hydrocarbon preservation risk for structural traps in the offshore bonaparte basin laminaria high the timor sea australian north west shelf the model results show that the distributions of shear strain and dilation as well as fluid flux are heterogeneous along fault planes inferring lateral variability of fault seal effectiveness the distribution of high shear strain is seen as the main control on structural permeability and is primarily influenced by the structural architecture prereactivation fault size and distribution within the modeled fault population as well as fault corrugations driven by growth processes represent key elements driving the partitioning of strain and up fault fluid flow these factors are critical in determining oil preservation during the late reactivation phase on the laminaria high testing of the model against leakage indicators defined on 3 d seismic data correlates with the numerical prediction of fault seal effectiveness and explains the complex distribution of paleo and preserved oil columns in the study area