neogene stratigraphy and the sedimentary and oceanographic development of the nw european atlantic margin a regional correlation of neogene stratigraphy has been attempted along and across the nw european atlantic continental margin between mid norway and sw ireland two unconformity bounded successions are recognised these are referred to as the lower and upper neogene successions and have been dated as miocene early pliocene and early pliocene holocene respectively in age their development is interpreted to reflect plate wide tectonically driven changes in the sedimentary oceanographic and latterly climatic evolution of the ne atlantic region the lower neogene succession mainly preserves a record of deep water sedimentation that indicates an expansion of contourite sediment drifts above submarine unconformities within this succession on both sides of the eastern greenland scotland ridge from the mid miocene this is interpreted to record enhanced deep water exchange through the faroe conduit deepest part of the southern gateway and can be linked to compressive inversion of the wyville thomson ridge complex thus a pervasive interconnected arctic north atlantic deep water circulation system is a neogene phenomenon the upper neogene succession records a regional change at about 4 ma in the patterns of contourite sedimentation submarine erosion new depocentres coeval with the onset of rapid seaward progradation of the continental margin by up to 100 km this build out of the shelf and slope is inferred to record a marked increase in sediment supply in response to uplift and tilting of the continental margin associated changes in deep water circulation may be part of an atlantic wide reorganisation of ocean bottom currents glacial sediments form a major component of the prograding shelf margin shelf slope sediment wedges but stratigraphic data indicate that the onset of progradation pre dates significant high latitude glaciation by at least 1 ma and expansive northern hemisphere glaciation by at least 3 ma

classification and composite diagnosis of extratropical cyclogenesis events in the southwest pacific abstract characteristic patterns of cyclogenesis in the southwest pacific region are identified from a sample of 40 developing cyclones during 1990 94 cases were chosen objectively to ensure a realistic sampling of typical rather than ideal events a subjective classification based on synoptic scale upper tropospheric flow signatures prior to cyclone intensification suggested four classes into which all but three cases fell three categories each containing about a quarter of the population involved direct coupling with the upper jet they represent cyclone formation beneath i the poleward exit region of a 300 hpa jet upstream from a diffluent trough class u ii the confluent equatorward entrance region of the upper wind maximum e and iii the upper jet exit region where the jet is downstream from the upper trough class d these are analogous to previously identified categories for the western north atlantic region a fourth class involved cyclones forming beneath a preexisting intense up

seven glacial cycles in the middle late pleistocene of northwest europe geomorphic evidence from buried tunnel valleys the deep ocean marine isotope record and the antarctic and greenland ice caps record numerous glacial and interglacial cycles since the middle pleistocene and yet evidence for similar numbers of ice sheet advances over the continent and shallow shelves of northwest europe is absent here we document seven generations of regionally correlatable subglacial tunnel valleys that record the geomorphic imprint of ice sheets traversing the north sea basin between ca 500 and 40 ka consistent with that predicted by proxy records of glacial and interglacial climate change over 180 subglacial tunnel valleys that incise into pleistocene sediments in the north sea basin were mapped over 60 000 km 2 of three dimensional seismic reflection data using a subset of these data we identified seven separate episodes of subglacial erosion that can be correlated regionally in the uk sector of the central north sea the characteristics of the valley morphologies orientations and infill stratigraphy indicate that each set of tunnel valleys formed during a separate ice sheet advance and retreat cycle stratigraphic data suggest that the tunnel valleys formed significantly later than the brunhes matuyama reversal event at 780 ka and before the last glacial maximum marine isotope stage mis 2 21 ka these results imply a more complicated glacial history for northwest europe and more glaciations than the three glaciation model traditionally interpreted from the terrestrial record for the past 500 k y our data provide the most complete documentary evidence for repeated advance and retreat of the northwest european ice sheets since the middle pleistocene and for the first time indicate that terrestrial ice sheet advances in the north sea can be matched in number with the cold events recorded in oceanic and or ice core proxies of climate change over the past 500 k y

formal ratification of the quaternary system period and the pleistocene series epoch with a base at 2 58 ma in june 2009 the executive committee of the international union of geological sciences iugs formally ratified a proposal by the international commission on stratigraphy to lower the base of the quaternary system period to the global stratotype section and point gssp of the gelasian stage age at monte san nicola sicily italy the gelasian until then had been the uppermost stage of the pliocene series epoch the base of the gelasian corresponds to marine isotope stage 103 and has an astronomically tuned age of 2 58 ma a proposal that the base of the pleistocene series epoch be lowered to coincide with that of the quaternary the gelasian gssp was also accepted by the iugs executive committee the gssp at vrica calabria italy which had hitherto defined the basal boundary of both the quaternary and the pleistocene remains available as the base of the calabrian stage age now the second stage of the revised pleistocene in ratifying these proposals the iugs has acknowledged the distinctive qualities of the quaternary by reaffirming it as a full system period correctly complied with the hierarchical requirements of the geological timescale by lowering the base of the pleistocene to that of the quaternary and fully respected the historical and widespread current usage of both the terms quaternary and pleistocene copyright 2009 john wiley sons ltd

acceleration of near surface strong winds in a dry idealised extratropical cyclone to understand near surface strong winds in extratropical cyclones a simulation of a dry idealised baroclinic wave is presented the forces that accelerate the winds are analysed using the terms in the horizontal momentum equation two regions of strong near surface winds developed within the simulation one to the east of the low centre and the other to the southwest the flow to the east resembling the cold conveyor belt accelerated as it passed through the strong pressure gradient associated with the warm frontal zone this acceleration was reduced by friction near the surface the winds to the southwest were characterised by three airstreams one airstream consisted of air parcels that started north of the warm front near the surface accelerated north of the warm front encircled the low and continued to accelerate to the southwest of the low the increases in wind speed in this airstream also part of the cold conveyor belt resulted from the along flow pressure gradient force being greater than friction the second airstream consisted of air parcels that descended west of the cold front and maintained their speed during descent until they were slowed either by friction in the boundary layer or as they moved southward against the local pressure gradient between these two airstreams a third airstream was characterised by air parcels that accelerated during descent from the mid to lower troposphere whilst moving around the bent back front this airstream bears some resemblance to the sting jet and was accelerated by the pressure gradient force on descent until it encountered increased friction or moved against the local pressure gradient

searching for the elusive cold type occluded front abstractaccording to the norwegian cyclone model whether a warm type or cold type occluded front forms depends upon which cold air mass is colder the prewarm frontal air mass or the postcold frontal air mass for example a cold type occlusion is said to occur when the occluded front slopes rearward with height because the prewarm frontal air mass is warmer than the postcold frontal air mass this temperature difference and the resulting occluded frontal structure in the norwegian cyclone model is part of what is called the temperature rule paradoxically no clear example of a rearward sloping cold type occluded front has been found in the literature even though the required temperature difference has been documented in several cases this article presents the first documented rearward sloping cold type occluded front this occluded front forms in a cyclone over the north atlantic ocean on 3 5 january 2003 and is documented in model output from the european centre for medium range weather forecasts

a characteristic life cycle of upper tropospheric cyclogenetic precursors during the experiment on rapidly intensifying cyclones over the atlantic erica abstract this paper documents a characteristic life cycle of upper tropospheric precursors to surface cyclogenesis observed during the field phase of the experiment on rapidly intensifying cyclones over the atlantic erica december 1988 february 1989 this life cycle begins with the development of an elongated region of lower dynamic tropopause that forms in association with an intensifying midtropospheric jet front over central north america the elongated disturbance subsequently compacts into a more circular configuration prior to crossing the east coast of north america and frequently is associated with rapid surface cyclogenesis offshore a representative example of the life cycle outlined above is documented through a detailed case study of the upper precursor associated with the second erica intensive observation period iop 2 cyclone emphasis is placed upon i description of the tropopause structure and evolution during the upper precursor life cycle ii diagnosis of mechanisms leading to t

the occurence and paleolimnologic significance of cutthroat trout oncorhynchus clarki in pluvial lakes of the estancia valley central new mexico cutthroat trout oncorhynchus clarki fossils in the quaternary age lacustrine sediment of the estancia valley provide insight into the paleolimnologic history of the valley the presence of fish is evidence that a pluvial system overflowed into the pecos river watershed most likely the overflow occurred during the expansion of early lake estancia an illinoian or pre illinoian pluvial lake known only in subcrop once established in the estancia watershed trout occupied headwater streams and only intermittently migrated and resided in developing lake systems the headwater streams served as refugia through the sangamon and early and middle wisconsin time when a fresh water lake did not exist in the valley with the advent of full pluvial conditions during the late wisconsin trout migrated from headwater streams into the first of three fresh water phases of late lake estancia on two occasions climate shifted to warmer and drier conditions causing significant lake level drawdown salinity increased and trout were eliminated from the lake only to be reintroduced during the next fresh water phase near the close of the late wisconsin late lake estancia waned and desiccated but headwater streams remained as fish refugia following the interpluvial episode the basin again filled culminating in lake willard considered to be of latest wisconsin age with evolution into a fresh water body trout migrated into a lake environment for the last time ensuing hot dry conditions brought about the desiccation of lake willard and severely impacted the headwater streams this factor in possible combination with human fishing activity led to the elimination of fish from the estancia valley after a continuous occupation of at least 130 000 yr

seismic modeling of gas chimneys we propose a simple acoustic model explaining the main features of gas chimneys the main elements of the model consist of gas diffusing from a connected fracture network and into the surrounding shale creating an inhomogeneous gas saturation the gas saturation results in an inhomogeneous fluctuating compressional velocity field that distorts seismic waves we model the fracture network by a randomwalk process constrained by maximum fracture length and angleofthefracturewithrespecttothevertical thegassaturation is computed from a simple analytical solution of the diffusion equation and pressure wave velocities are locally obtained assuming that mixing of shale and gas occurs on a scalemuchsmallerthanseismicwavelengths syntheticseismic sections are then computed using the resulting inhomogeneous velocity model and shown to give rise to similar deterioration in data quality as that found in data from real gas chimneys also synthetic common midpointcmpgathers show the same distorted and attenuated traveltime curves as those obtained from a real data set the model shows clearly thatthefeaturesofgaschimneyschangewithgeologicaltime a model parameter in our approach the deterioration of seismicwavesbeingsmallestjustafterthecreationofthegas chimney it seems likely that at least some of the features of gas chimneys can be explained by a simple elastic model in combinationwithgasdiffusionfromafracturenetwork

discrimination between pressure and fluid saturation changes from time lapse seismic data explicit expressions for computing saturation and pressure related changes from time lapse seismic data have been derived and tested on a real time lapse seismic data set necessary input is near and far offset stacks for the baseline seismic survey and the repeat survey the method has been tested successfully in a segment where pressure measurements in two wells verify a pore pressure increase of 5 to 6 mpa between the baseline survey and the monitor survey estimated pressure changes using the proposed relationships fit very well with observations between the baseline and monitor seismic surveys 27 of the estimated recoverable hydrocarbon reserves were produced from this segment the estimated saturation changes also agree well with observed changes apart from some areas in the water zone that are mapped as being exposed to saturation changes which is unlikely saturation changes in other segments close to the original oil water contact and the top reservoir interface are also estimated and conf

baroclinic development within zonally varying flows previous idealized modelling studies have shown the importance of across jet barotropic shear to the resulting evolution of cyclones anticyclones surface based fronts and upper level fronts meanwhile many observational studies of cyclones have shown the importance of along jet variations in the horizontal wind speed i e confluence and diffluence this study investigates the importance of these along jet zonal for zonally oriented jets variations in the horizontal wind speed to the resulting structures and evolutions of baroclinic waves using idealized models of growing baroclinic waves an idealized primitive equation channel model is configured with growing baroclinic perturbations embedded within confluent and diffluent background flows when the baroclinic perturbations are placed in background confluence the lower tropospheric frontal structure and evolution initially resemble the shapiro keyser cyclone model with a zonally oriented cyclone strong warm front and bent back warm front later as the baroclinic wave is amplified in the stronger downstream baroclinicity the warm sector of the cyclone narrows becoming more reminiscent of the norwegian cyclone model the upper level frontal structure develops with a southwest northeast orientation and becomes strongest at the base of the trough where geostrophic cold advection is occurring in contrast when the baroclinic perturbations are placed in background diffluence the lower tropospheric frontal structure and evolution resemble the norwegian cyclone model with a meridionally oriented cyclone strong cold front and occluded front the upper level frontal structure is initially oriented northwest southeast on the western side of the trough before becoming zonally oriented weak geostrophic temperature advection occurs along its length these results are compared to those from previous observational and idealized modelling studies copyright 2007 royal meteorological society

palaeomagnetic evidence for early pleistocene in the central and northern north sea the palaeomagnetic evidence presented here refutes the earlier hypothesis that most of the quaternary succession in the central north sea area is of middle to upper weichselian age a study of the quaternary seismic stratigraphy has been tied to 11 cored boreholes which are being examined for their physical properties and faunal content initial palaeomagnetic studies show a major reversely magnetized zone which can be correlated from borehole to borehole and with the seismic stratigraphy this reversely magnetized zone is thought to represent the matuyama epoch which ended 790 000 yr bp consequently this suggests the presence of early pleistocene strata in the central and northern north sea

the influence of the 1997 99 el niňo southern oscillation on extratropical baroclinic life cycles over the eastern north pacific the el nino southern oscillation enso strongly influences the interannual and seasonal atmospheric circulation over the north pacific the present study shows that the meridional displacement of the time mean upper level jet associated with enso modulates the time mean barotropic meridional wind shear over the central and eastern north pacific storm track earlier theoretical and observational studies established the influence of barotropic wind shear on the life cycles of extratropical cyclones and their upper level potential vorticity pv waves the present study suggests that differences in the time mean flow associated with the 1997 99 enso cycle had a similar impact on tropopause pv structure meridional eddy fluxes of momentum and temperature and predictability

two paradigms of baroclinic wave life cycle behaviour two idealized baroclinic wave 6 life cycles examined here suggest a framework of opposite extremes a in which to view the behaviour of real synoptic scale disturbances in middle latitudes and b in which to interrelate the synoptic and wave theoretic viewpoints using the saturation propagation saturation sps picture of wave 6 life cycle behaviour the two life cycles dented by lc1 and lc2 are higher resolution versions of the simmons hoskins basic and anomalous cases showing strong and weak late decay of eddy kinetic energy eke they illustrate in varying degrees two extreme types of behaviour here disignated anticyclonic and cyclonic and epitomized by strongly contrasting upper air trough behaviour anticyclonic behaviour dominates the late stages of lc1 and is characterized by backward tilted thinning troughs being advected anticyclonically and equatorward as in the commoner cases of planetary scale mid stratospheric rossby wave breaking cyclonic behaviour dominates lc2 and is characterized by forward tilted broadening troughs wrapping themselves up cyclonically and poleward producing major cut off cyclones in high latitudes these morphologies are visualized by upper air maps of potential temperature on the nominal tropopause defined as a constant potential vorticity surface some atmospheric mid latitude disturbances examined here using the same visualization applied to operational analyses show the same two extreme types of trough behaviour together with intermediate cases the sps picture is re examined using eliassen palm and refractive index cross sections it is shown in particular by reference to a wave activity theorem of haynes that the late stages of lc2 can be looked upon as a remarkably clear and morphologically novel large amplitude counterpart of the nonlinear reflection scenario of rossby wave critical layer theory the late stages of lc1 by constrast look more akin to an nonlinear critical layer absorption scenario lc2 exhibits region of largely undular pv contours adjacent to a nonlinear of irreversiby deformen pv contous in the latter region pv rearrangement and hence absorption of rossby wave activity has largely ceased this accounts for the more persistent ekee in the lc2 case

the effect of large scale flow on low level frontal structure and evolution in midlatitude cyclones abstract observational and modeling studies documented in the literature indicate that the large scale flow has an important effect on the structure and evolution of low level fronts in midlatitude cyclones the purpose of this paper is to address the role of the large scale flow on low level cyclone frontal structure and evolution through a combined observational and idealized modeling approach analyses of two observed cyclone cases embedded in large scale diffluence and confluence respectively are presented to illustrate two possible cyclone frontal structures and evolutions specifically the cyclone moving into a diffluent high amplitude ridge becomes meridionally elongated and possesses a strong meridionally oriented cold front and a weak warm front the cold front rotates into the warm front forming an occluded front in the manner of the norwegian cyclone model as indicated by the narrowing of the thermal ridge connecting the warm sector to the cyclone center in contrast the cyclone moving i

a pv view of zonal flow vacillation abstract it is suggested here that the zonal flow vacillation of the southern hemisphere is caused by a mutual interaction between the barotropic shear of the zonal flow and the evolution of baroclinic eddies during the later stages of their lifecycle an index of the zonal wind anomaly difference between 40 and 60 s is defined for a 13 yr record of european centre for medium range weather forecasts ecmwf analyses periods are selected during which the zonal flow is at the extremes of its characteristic vacillation which are distinguished by a broad westerly jet with minor maxima near 30 and 60 s and a narrower jet peaked near 40 s the narrower 40 s jet has stronger cyclonic shear across the baroclinic zone these changes are accompanied by shifts in poleward eddy momentum flux on the 500 hpa surface and potential vorticity fluxes on the theta surfaces that lie in the midtroposphere which are both consistent with the maintenance of the zonal wind anomalies against friction series of synoptic maps

weighted stacking for rock property estimation and detection of gas amplitude versus offset concepts can be used to generate weighted stacking schemes here called geo stack which can be used in an otherwise standard seismic data processing sequence to display information about rock properties the zoeppritz equations can be simplified and several different approximations appear in the literature they describe the variation of p wave reflection coefficients with the angle of incidence of a p wave as a function of the p wave velocities the s wave velocities and the densities above and below an interface using a smooth representative interval velocity model from boreholes or velocity analyses and assuming no dip the angle of incidence can be found as a function of time and offset by iterative ray tracing in particular the angle of incidence can be computed for each sample in a normal moveout corrected cmp gather the approximated zoeppritz equation can then be fitted to the amplitudes of all the traces at each time sample of the gather and certain rock properties can be estimated the estimation of the rock properties is achieved by the application of time and offset variant weights to the data samples before stacking the properties which can be displayed by geo stack are p wave reflectivity or true zero offset reflectivity s wave reflectivity and the reflectivity of p wave velocity divided by s wave velocity or pseudo poisson s ratio reflectivity if assumptions are made about the relation between p wave velocity and s wave velocity for water bearing clastic silicate rocks then it is possible to create a display which highlights the presence of gas

high resolution seismic profile through a late cenozoic delta complex in the southern north sea abstract a digitally recorded and processed multichannel seismic profile between cromer england and sylt germany has provided the first continuous section through the miocene to middle pleistocene delta complex of the southern north sea basin the profile depicts the progressive westward expansion of deltaic sedimentation that eventually filled in this gently subsiding epicontinental basin significant basinward shifts in seismic facies occur above all but one of 14 seismic sequence boundaries that punctuate the deposition of up to 830 m of deltaic sediments on the profile these sequence boundaries and the morphology of prodelta delta front delta top and fluvio deltaic seismic facies record the interaction between subsidence cyclic fluctuation in sediment supply to and cyclic change of relative sea level within the basin two submarine slides were developed within delta front facies in the pliocene section and the profile has intersected a swarm of elsterian middle pleistocene glacial palaeovalleys that have been incised into the upper part of the delta complex

upper level frontogenesis associated with the birth of mobile troughs in northwesterly flow previous studies have shown that 500 hpa mobile trough births or genesis occur preferentially in northwesterly flow during upper level frontogenesis and that cold advection assists in and is a product of mobile trough intensification this study focuses on the synoptic environments and thermal advection patterns of upperlevel fronts associated with mobile trough births in northwesterly flow a climatology of 186 such events derived from an earlier study by sanders shows that most births tend to occur within uniform or diffluent flow and that most tend to be associated with relatively weaker 500 hpa thermal advection most mobile trough births in diffluence however tend to be associated with increasing 500 hpa cold advection typically indicated by a cyclonic rotation of isentropes whereas most mobile trough births in confluence tend to be associated with weaker 500 hpa thermal advection two cases of upper level frontogenesis associated with mobile trough genesis one in diffluence and one in confluence are compared to determine the processes acting to produce the differing thermal advection patterns at 500 hpa a thermal advection tendency equation is developed and shows that the magnitude of the temperature advection can be changed by accelerating the advecting wind speed or by changing the temperature gradient i e vector frontogenesis the latter can be accomplished either by changing the magnitude of the temperature gradient the frontogenetical component fn also known as scalar frontogenesis or by rotating the direction of the temperature gradient relative to the flow the rotational component fs the dominant processes acting on fn for the diffluence and confluence cases are tilting and deformation frontogenesis respectively the dominant process acting on fs for the diffluence case is rotation of the isentropes due to the vorticity term whereas rotation of the isentropes due to the vorticity and tilting terms are both important for the confluence case the rotational component of frontogenesis is cyclonic downstream of the vorticity maximum for both cases favoring increasing cold advection downstream of the vorticity maximum for both cases the rate of rotation of the isentropes at a point due to horizontal advection is large and that due to vertical advection is negligible since advection can only transport the existing isentrope angle and cannot change the isentrope angle the rotational component of frontogenesis normalized by the temperature gradient is the only term that can increase the isentrope angle following the flow this term dominates in the diffluence case but is small in the confluence case this diagnosis suggests the following reasoning in diffluent flow the vorticity associated with the incipient trough is compacted into a more circular shape and intensifies the potent vorticity maximum leads to robust isentrope rotation in confluent flow however the vorticity is deformed into an elongated maximum inhibiting both strong isentrope rotation and increasing cold advection thus the rotational frontogenesis component explains the rotation of the isentropes that is responsible for the differing thermal advection patterns diagnosis of these cases supports the results from the climatology indicating a strong relationship between the synoptic environment and the upper tropospheric thermal advection pattern nevertheless current conceptual models of upper level frontogenesis do not fully explain the variety of these features in the real atmosphere in particular mobile trough genesis and its associated upper level frontogenesis can occur in weak 500 hpa thermaladvection patterns in contrast to the confluence and cold advection that have been previously identified as important to upper level frontal intensification this result provides further support for the possibility that generation and intensification of mobile troughs can occur by barotropic processes

avo inversion theory and practice avo inversion is an area of research which attempts to go beyond the qualitative process of avo interpretation currently used to predict the presence of gas in a sand

evidence for late pleistocene ice stream activity in the witch ground basin central north sea from 3d seismic reflection data abstract buried submarine landforms mapped on 3d reflection seismic data sets provide the first glacial geomorphic evidence for glacial occupation of the central north sea by two palaeo ice streams between 58 59 n and 0 1 e streamlined subglacial bedforms mega scale glacial lineations and iceberg plough marks within the top 80 m of the quaternary sequence record the presence and subsequent break up of fast flowing grounded ice sheets in the region during the late pleistocene the lengths of individual mega scale glacial lineations vary from 5 to 20 km and the distance between lineations typically ranges from 100 to 1000 m the lineations incise to a depth of 10 12 m with trough widths of 100 m the most extensive and best preserved set of lineations is attributed to the action of a late weichselian ice stream which either drained the ne sector of the british irish ice sheet or was sourced from the sw within the fennoscandian ice sheet the 30 50 km wide palaeo ice stream is imaged along its flow direction for 90 km trending nw se an older set of less well preserved lineations is interpreted as an earlier weichselian or saalian ice stream and records ice flow in an sw ne orientation cored sedimentary records tied to 3d seismic observations support grounded ice sheet coverage in the central north sea during the last glaciation and indicate that ice flowed over a muddy substrate that is interpreted as a deformation till the identification of a late weichselian ice stream in the witch ground area of the north sea basin provides independent geomorphic evidence in support of ice sheet reconstructions that favour complete ice coverage of the north sea between scotland and norway during the last glacial maximum

high frequency sequence stratigraphy of upper cenozoic deposits in the central and southeastern north sea areas abstract during late cenozoic times southwestward prograding deposits filled in the central and southern part of the epicontinental north sea basin the ringkobing fyn high acted as a topographical high partly separating the central and southeastern north sea into two embayments which were connected towards the west by a deeper seaway located in the central graben area the stratal geometry deduced from seismic sections indicates different basin physiography subsidence rates and sediment influx between the two embayments eustatic sea level cycles of several frequencies interacted with low subsidence rates in the southern embayment to generate composite relative sea level cycles each composed of relative sea level cycles of higher frequencies forty five upper cenozoic sequences are identified in the southern embayment whereas only 21 sequences are recognized in the northern embayment major hiati and intervals of starved sedimentation may therefore be present in the northern embayment the sequences stack into nine composite sequences each reflecting a depositional cycle representing lowstand succeeded by transgressive highstand conditions in general a composite sequence is characterized by a period of increasing sediment accumulation rates

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

initiation and evolution of an intense upper level front abstract within confluent northwesterly flow of an intensifying baroclinic wave over north america in late october 1963 an intense frontal zone developed in 12 h near the inflection point in the middle and upper troposphere by 24 h after its initial appearance the zone extended roughly from 400 to 700 mb and from the inflection point to just beyond the downstream trough horizontal gradients of potential temperature reached 15 20 k 100 km 1 air within the frontal zone was extremely dry as the accompanying trough approached the east coast of he united states surface frontogenesis occurred offshore remaining distinct from the upper level front a region of subsidence elongated in the direction of the upper level flow displayed maximum descent on the warm edge of the frontal zone and played a frontogenetical role through tilting of the isentropic surfaces analysis of isentropic potential vorticity showed significant increase of this quantity near the cold base and a probable decrease near the top

evolution of mesoscale precipitation band environments within the comma head of northeast u s cyclones abstract this paper explores the mesoscale forcing and stability evolution of intense precipitation bands in the comma head sector of extratropical cyclones using the 32 km north american regional reanalysis hourly 20 km rapid update cycle analyses and 2 km composite radar reflectivity data a statistical and composite analysis of 36 banded events occurring during the 2002 08 cool seasons reveals a common cyclone evolution and associated band life cycle a majority 61 of banded events develop along the northern portion of a hook shaped upper level potential vorticity pv anomaly during the 6 h leading up to band formation lower tropospheric frontogenesis nearly doubles and the conditional stability above the frontal zone is reduced the frontogenesis increase is primarily due to changes in the kinematic flow associated with the development of a mesoscale geopotential height trough this trough extends poleward of the 700 hpa low and is the vertical extension of the surface warm front and surface

a five year radar based climatology of tropopause folds and deep convection over wales united kingdom abstracta five year 2006 10 radar based climatology of tropopause folds and convective storms was constructed for wales united kingdom to determine how deep moist convection is modulated by tropopause folds based on the continuous high resolution data from a very high frequency vhf wind profiling radar located at capel dewi wales 183 tropopause folds were identified tropopause folds were most frequent in january with a secondary maximum in july based on data from the u k weather radar network a climatology of 685 convective storms was developed the occurrence of convective storms was relatively high year round except for an abrupt minimum in february april multicellular lines 43 5 were the most common morphology with a maximum in october followed by isolated cells 33 1 with a maximum in may september and nonlinear clusters 23 4 with a maximum in november january convective storms were associated with 104 56 8 of the tropopause folds identified in this study with the associ

buried iceberg ploughmarks in the early quaternary sediments of the central north sea a two million year record of glacial influence from 3d seismic data abstract buried linear to curvilinear depressions interpreted as iceberg ploughmarks were identified through most of the 2 ma long and about 700 m thick early quaternary sedimentary record in two 3d seismic cubes from the central north sea basin 56 58 n 2 3 e the mean width of 402 features measured at 6 time slices in cube c08 was between 49 and 63 m and mean length was 2 5 to 3 7 km mapping the

gas seepage as an indicator of deeper prospective reservoirs a study based on exploration 3d seismic data three periods of sustained gas seepage in geological time have been revealed in danish block 5604 26 in the north sea by the use of exploration 3d seismic data the most recent period is indicated by a cluster of seismic chimneys which ties in to buried craters near the seabed and possible present gas escape through the seabed along with amplitude anomalies indicating a shallow gas sand charged by gas migrating from a deeper level the cluster of seismic chimneys indicative of vertical gas migration is visible down to 1 5 s twt 1500 ms and therefore the gas is interpreted as migrating from a deeper stratigraphic horizon below this level it becomes difficult to see the chimneys due to complex faulting the faults may work as gas migration pathways the geometry of the cluster of seismic chimneys indicates that the gas has been migrating from one point the nearest possible source of the gas is an underlying prospect where an oil and gas discovery has been made two earlier periods of gas seepage are indicated by mounds possibly carbonate buildups over gas seepages in pliocene time and similarly buried craters formed by gas seepages in an earlier period in pliocene time the results of this study are that gas seepage is a periodical process in geological time and that its presence and associated features can be used as an indicator of deeper prospective reservoirs

an analysis of frontogenesis in numerical simulations of baroclinic waves abstract using a primitive equation pe model we revisit two canonical flows that were previously studied using a semigeostrophic equation sg model in a previous paper the authors showed that the pe and the sg models can have significantly different versions of the large scale dynamics here they report on the implications of this difference for frontogenesis the program for the study of frontogenesis developed by b j hoskins and collaborators is followed to show how in the pe version of the canonical cases the surface warm front develops before the cold front and why the upper level front is a long nearly continuous feature going from ridge to trough the frontogenesis experienced by an air parcel is computed following the parcel to illustrate better the mechanisms involved as the present calculations are carried out longer than most previous ones the relation of the upper frontogenesis to the formation of the upper level cutoff cyclone is also examined trajectory and three dimensional g

conceptual models of upper level frontogenesis in south westerly and north westerly flow the conceptual model proposed by shapiro as it is applied to the evolution of an upper level frontal zone within a baroclinic wave is reviewed and its limitations are investigated through previous literature and two casestudies presented in this paper the early stages in the evolutions of these two cases are used to examine specific limitations of this conceptual model 1 upper level frontogenesis in south westerly flow that evolves from a state of equivalent barotropy to a state of cold advection along the front and 2 upper level frontogenesis in northwesterly flow with along front variation in the sign of the thermal advection such that warm advection occurs upstream of cold advection in the thermal trough vector frontogenesis diagnostics for the lagrangian rate of change of the magnitude and direction of the horizontal potential temperature gradient including tilting due to vertical motion are derived these diagnostics are applied to the two cases to examine the maintenance of the potential temperature gradient and the development of cold advection along each upper level front the upper level front in south westerly north westerly flow was maintained primarily by deformation tilting frontogenesis in agreement with previous research the increasing cold advection along the upper level front in both cases was related to an upstream vorticity maximum for the case in south westerly flow the pre existing vorticity maximum approached a downstream equivalent barotropic upper level front in a manner similar to an instant occlusion resulting in cold advection along the length of the upper level front for the case in north westerly flow an intensifying vorticity maximum concentrated the cold advection in the base of the thermal trough as warm advection developed upstream these two cases are compared to upper level fronts in previous literature and a climatology of upper level fronts associated with landfalling cyclones over the eastern north pacific ocean the results indicate that these two cases are typical of early evolutions of upper level fronts that can occur in south westerly and north westerly flow therefore a revised version of the shapiro conceptual model is presented that represents more accurately the early evolutions exhibited in the present and previous studies

comments on the influence of rotational frontogenesis and its associated shearwise vertical motions on the development of an upper level front by a a lang and j e martin january a 2010 136 239 252 two previous studies by rotunno et al 1994 j atmos sci 51 3373 3398 and schultz and doswell 1999 q j r meteorol soc 125 2535 2562 offer conflicting views on the origin of geostrophic cold air advection that is sometimes present during upper level frontogenesis although lang and martin 2010 claim to reconcile these two studies this comment offers four reasons why reconciliation is not possible first the necessary calculations to compare the tilting frontogenesis term to the horizontal frontogenesis terms are not performed second the thermal advection tendency or isentrope orientation tendency in the region of the developing cold air advection is not calculated third previous studies showing that the vertical terms in these diagnostics are likely associated with warm air advection not cold air advection are not disproven this fact also may explain the predominance of relatively weak geostrophic thermal advection in climatologies of upper level fronts fourth concerns are raised about some of the statements made in lang and martin 2010 these comments also fix an error in eq 11 in schultz and doswell 1999 copyright 2012 royal meteorological society

3d seismic geomorphology of a large plio pleistocene delta bright spots and contourites in the southern north sea abstract regional 2d seismic interpretation has been integrated with high resolution 3d interpretation in dutch offshore blocks a f in the southern north sea 17 horizons mmu s1 s4 s4 1 s4 2 s5 s5 1 s6 s13 and 14 seismic units were interpreted expanding upon studies by kuhlmann and wong 2008 the study presents detailed and extensive twt structure and thickness maps of key depositional units allowing paleogeographic reconstructions detailed analysis of incisional scour marks and hypothesised iceberg scours and constructional features contourites identified initially by bright spots on seismic data linked to bottom currents was undertaken paleo paleographic reconstructions of water depth emphasise the role of hypothesised tidally generated contour currents in the late stage deltaic infill of an epicontinental basin north sea

the palette of fronts and cyclones within a baroclinic wave development abstract a study is undertaken of the concurrent development of fronts and cyclones within a growing baroclinic wave the dynamical framework for the study is that of the semigeostrophic adiabatic flow of a uniform potential vorticity atmosphere that is sandwiched between two horizontal plates on an f plane a three dimensional spectral model is used to examine the growth to finite amplitude of the normal modes of this system for basic states that comprise of a symmetric jetlike baroclinic flow with and without a superposition of a uniform barotropic shear of either cyclonic or anticyclonic vorticity it is demonstrated that the presence of such lateral shear in the ambient environment exerts a profound influence upon the ensuing palette of fronts and cyclones on the synoptic scale this flow component influences the scale and strength of the individual surface highs and lows and also modifies the extent of their lateral drift away from and their relative movement along the baroclinic zone aloft t

effects of surface drag on fronts within numerically simulated baroclinic waves abstract a comparative analysis of simulations of baroclinic waves with and without surface drag is presented with particular reference to surface features as in recent studies the present simulations show that compared to simulations with no drag those with surface drag are less inclined to develop a secluded warm sector and that drag weakens the warm front while the cold front remains strong the authors demonstrate that analogous effects occur when ekman pumping is used in nonlinear quasigeostrophic numerical simulations of unstable baroclinic waves in a channel however since the quasigeostrophic model produces symmetric highs and lows in the unstable baroclinic wave the cold and warm fronts are therefore also symmetric and hence equally affected by the ekman pumping the different effect that friction has on the warm front with respect to the cold front in the primitive equation simulations is fundamentally related to the tendency for the lows to be strong and narrow and the highs weak and br

iceberg ploughmarks illuminated by shallow gas in the central north sea 2014 the authors published by elsevier ltd this is an open access article under the cc by nc salicense http creativecommons org licenses by nc sa 3 0

a relict ice scoured erosion surface in the central north sea abstract the interpretation of shallow seismic records from the central north sea has revealed the existence of an irregular erosion surface within late pleistocene sediments a morphological study of this surface has identified two main types of relief 1 an irregular rough topography with depressions varying in depth from 1 to 6 m and in width from 25 to 300 m and 2 a much smoother topography with relatively few depressions on a palaeobathymetric map the rough topography extends from ca 110 to 160 m below sea level od while the smoother topography extends beyond the 160 m below od contour this surface is interpreted as an ice scoured erosional feature formed by the grounding of sea ice in a shallow shelf environment the stratigraphic position of the ice scoured surface shows it to be a relict late weichselian feature formed at ca 17 000 18 000 b p

pliocene paleoenvironment evolution as interpreted from 3d seismic data in the southern north sea dutch offshore sector a high resolution 3d seismic survey from the dutch offshore sector has been interpreted and subsequently correlated with existing regional seismo stratigraphic concepts derived from conventional 2d seismic data sets the interpreted 13 seismic units have been related to a newly established chrono stratigraphic framework kuhlmann et al 2006a b chronostratigraphy of late neogene sediments in the southern north sea basin and paleoenvironmental interpretations palaeogeography palaeoclimatology palaeoecology 239 426 455 integrated chronostratigraphy of the pliocene pleistocene interval and its relation to the regional stratigraphical stages in the southern north sea region netherlands journal of geosciences geologie en mijnbouw 85 1 19 35 resulting in up dated age control for the seismic units the generation of amplitude maps time slices and isopach maps from the 3d seismic data enabled detailed spatial and temporal reconstruction regarding the paleoenvironmental and climatological development as depicted by kuhlmann et al 2006a chronostratigraphy of late neogene sediments in the southern north sea basin and paleoenvironmental interpretations palaeogeography palaeoclimatology palaeoecology 239 426 455 the lowermost seismic units s1 s4 comprise condensed middle miocene to piacencian sediments deposited under warm open marine conditions these sediments show a uniform seismic facies of low amplitude reflectors the boundary of seismic unit s4 s5 around 2 6 ma delineates a shift towards generally colder climate conditions that are connected to the onset of northern hemisphere glaciation seismic unit s5 includes alternations of warmer and colder periods during warmer periods bottom currents generated elongated structures 2 5 4 km long 300 500 m wide on the horizon display these layers show as well shallow gas accumulations with a more regional extent and are related to coarser grained sediments sealed by clayey sediments of the cold phases a homogenous seismic facies is characteristic for the colder periods within seismic units s6 and s7 internal fore set structures display the regressional trend related to the cooling of this interval seismic units s8 s11 display a pattern of unoriented lineaments which was probably caused by icebergs drifting into the north sea and souring the sea floor this finding is in accordance with the shallow marine arctic conditions of this interval within these units a bright spot of 3 by 7 km in size is interpreted to result from shallow gas accumulation related to a grounded iceberg this feature represents another more local area of gas accumulation that is closely related to iceberg activity within the study area the uppermost seismic units s12 and s13 belong to a fluvial paralic paleo environment that is characterised by aggradational seismic reflectors pleistocene glacial valleys were recognised in the upper 200 m below sea floor 2007 elsevier ltd all rights reserved

iceberg scouring in scoresby sund and on the east greenland continental shelf modern and relict scours produced by iceberg keels have been reported from a number of high latitude continental shelves in the northern hemisphere and antarctica but observations are largely absent from the east greenland shelf about 18 km3 yr 1 of icebergs are calved into the scoresby sund fjord system east greenland these icebergs have submarine keels with drafts up to 550 m modern iceberg contacts with the sea floor are inferred from calculated keel depths and stationary icebergs identified on sequential landsat imagery acoustic profiles parasound 3 5 khz of the sea floor show that scouring is a significant process in water depths 550 m iceberg scouring intensity varies inversely with water depth the most intense scouring occurs at depths of 300 400 m iceberg scours were observed on over 25 000 km2 of the east greenland shelf at 69 72 n and 75 n scours are being actively produced on the modern shelf but relict scours probably dating back to the late weichselian are also present the rate of iceberg production from greenland ice sheet outlet glaciers and iceberg drift tracks on the shelf suggests that iceberg scouring is important over a significant proportion of the 500 000 km2 area above the shelf break around greenland

breaking waves at the tropopause in the wintertime northern hemisphere climatological analyses of the orientation and the theoretical lc1 2 classification abstract breaking waves on the tropopause are viewed as potential vorticity pv streamers on middle world isentropic levels a northern hemisphere winter climatology of the streamers spatial distribution and meridional orientation is derived from the 40 yr ecmwf re analysis era 40 dataset and used to assess the nature and frequency of occurrence of breaking synoptic scale waves the streamers are grouped into two classes related to the so called cyclonic lc2 and anticyclonic lc1 patterns and the ambient wind strength and wind shear is also noted it is shown that the occurrence of cyclonic and anticyclonic pv streamers exhibits a distinct spatial variability in the horizontal and the vertical the majority of cyclonic pv streamers are found on lower isentropic levels that intersect the tropopause at more poleward latitudes whereas anticyclonic streamers predominate at higher elevations in the subtropics an analysis of the streamer patterns for the two phases of the north atlantic oscillation

amplitude versus offset variations in gas sands seismic reflections from gas sands exhibit a wide range of amplitude versus offset avo characteristics the two factors that most strongly determine the avo behavior of a gas sand reflection are the normal incidence reflection coefficient r0 and the contrast in poisson s ratio at the reflector of these two factors r0 is the least constrained based on their avo characteristics gas sand reflectors can be grouped into three classes defined in terms of r0 at the top of the gas sand class 1 gas sands have higher impedance than the encasing shale with relatively large positive values for r0 class 2 gas sands have nearly the same impedance as the encasing shale and are characterized by values of r0 near zero class 3 sands have lower impedance than the encasing shale with negative large magnitude values for r0 each of these sand classes has a distinct avo characteristic an example of a gas sand from each of the three classes is presented in the paper the class 1 example involves a hartshorn channel s

the history of quaternary sedimentation in the uk sector of the north sea basin reconnaissance seismic and sampling surveys have shown that up to 500 m of lower and early middle pleistocene deltaic sediments are preserved in the uk sector of the north sea the distributions of delta related facies record the progressive expansion of peripheral delta systems northwards across the southern north sea during the early pleistocene a late middle pleistocene unconformity is present throughout the uk sector and sedimentation above the unconformity was dominated by glacial erosional and depositional processes a complex system of deeply incised valleys was eroded during each of three regional middle and upper pleistocene glaciations and the valleys have been filled or partially filled by glaciolacustrine or glaciomarine and interglacial marine sediments the valleys of the earliest elsterian glaciation are up to 400 m deep in the southern north sea the saalian and weichselian valleys are commonly more than 100 m deep they are eroded through their contemporary tills nearshore but occur well beyond the limits of these tills offshore the origins of these valleys are attributed to a combination of fluvial subglacial and periglacial processes

generation of mesoscale gravity waves in upper tropospheric jet front systems abstract multiply nested mesoscale numerical simulations with horizontal resolution up to 3 3 km are performed to study the generation of mesoscale gravity waves during the life cycle of idealized baroclinic jet front systems long lived vertically propagating mesoscale gravity waves with horizontal wavelengths 100 200 km are simulated originating from the exit region of the upper tropospheric jet streak in a manner consistent with past observational studies the residual of the nonlinear balance equation is found to be a useful index in diagnosing flow imbalance and predicting wave generation the imbalance diagnosis and model simulations suggest that balance adjustment as a generalization of geostrophic adjustment is likely responsible for generating these mesoscale gravity waves it is hypothesized that through balance adjustment the continuous generation of flow imbalance from the developing baroclinic wave will lead to the continuous radiation of gravity waves

response of baroclinic life cycles to barotropic shear abstract cyclonic barotropic shear of incrementally increasing magnitude is imposed on an idealized midlatitude jet and the life cycles of baroclinically unstable wavenumber 6 perturbations growing on these jets are studied when the barotropic shear parameter passes a critical value the life cycle makes an abrupt transition from anticyclonic to cyclonic behavior the abrupt transition in behavior is most evident in the barotropic decay of eddy kinetic energy in the structure of the eddies as seen in potential vorticity maps and in the nature of the zonal flow accelerations produced during the life cycle it is suggested that the abrupt transition can be interpreted as arising from a positive feedback between eddy propagation and eddy induced zonal flow accelerations dependences on the zonal scale of the eddy are also investigated wavenumber 8 exhibits cyclonic behavior while wavenumber 4 exhibits anticyclonic behavior for all values of cyclonic shear considered this dependence on zonal scale is c

morphology sedimentary infill and depositional environments of the early quaternary north sea basin 56 62 n abstract the north sea basin has been subsiding during the quaternary and contains hundreds of metres of fill seismic surveys 170 000 km2 provide new evidence on early quaternary sedimentation from about 2 75 ma to around the brunhes matuyama boundary 0 78 ma we present an informal seismic stratigraphy for the early quaternary of the north sea and calculate sediment volumes for major units early quaternary sediment thickness is 1000 m in the northern basin and 700 m in the central basin total about 40 000 km3 northern north sea basin fill comprises several clinoform units prograding westward over 60 000 km2 architecture of the central basin also comprises clinoforms building from the southeast to the west an acoustically layered and mounded unit unit z was deposited remaining accommodation space was filled with fine grained sediments of two central basin units above these units an upper regional unconformity equivalent uru records a conformable surface with flat lying units that indicate stronger direct glacial influence than on the sediments below on the north sea plateau north of 59 n the upper regional unconformity uru is defined by a shift from westward to eastward dipping seismic reflectors recording a major change in sedimentation with the shetland platform becoming a significant source a model of early quaternary sediment delivery to the north sea shows sources from the scandinavian ice sheet and major european rivers clinoforms prograding west in the northern north sea basin representing glacigenic debris flows indicate an ice sheet on the western scandinavian margin in the central basin sediments are generally fine grained suggesting a distal fluvial or glacifluvial origin from european rivers ploughmarks also demonstrate that icebergs derived from an ice sheet to the north drifted into the central north sea basin by contrast sediments and glacial landforms above the uru provide evidence for the later presence of a grounded ice sheet

sting jets in extratropical cyclones a review this paper reviews the current state of knowledge of sting jets in extratropical cyclones sting jets were formally identified in 2004 by the pioneering work of keith browning reviewing this and subsequent studies we define the sting jet as a coherent air flow that descends from mid levels inside the cloud head into the frontal fracture region of a shapiro keyser cyclone over a period of a few hours leading to a distinct region of near surface stronger winds it therefore lies above the cold conveyor belt during some stage its life but at least in some cases descends to reach the top of boundary layer ahead of the cold conveyor belt it is not attributed to a specific mechanism in this definition we conclude that it is likely that a continuum of sting jet descent and speed up mechanisms exists at one extreme is balanced descent partly associated with frontolysis in the frontal fracture region more horizontally small scale and stronger frontolytic descent may occur associated with weak stability to slantwise convective downdraughts instability to slantwise convective downdraughts may occur in some systems leading to multiple slantwise convective downdraughts associated with the release of conditional symmetric instability and even possibly symmetric instability the global climatology of sting jets and the interaction between the atmospheric boundary layer and sting jets are revealed as specific areas where more research is needed finally we describe eight myths and misunderstandings that exist in the current literature with the aim of guiding future research into the sting jet phenomenon

synergistic use of satellite observations and numerical weather model to study atmospheric occluded fronts synthetic aperture radar sar images reveal the surface imprints of atmospheric occluded fronts an occluded front is characterized as a low wind zone located between and within two zones of higher winds blowing in the opposite directions on the left and right sides of the occluded front a group of four sar images reveal that the width of an individual occluded frontal zone and the wind magnitudes outside fronts vary greatly from case to case in this paper we performed a case study to analyze an occluded front observed by an environmental satellite envisat advanced sar and ascat scatterometer along the west coast of canada on november 24 2011 the two way interactive triply nested grid 9 3 1 km weather research and forecasting wrf model was utilized to simulate the evolution of the occluded front the occluded front moved toward the east during a 24 h model simulation and the movement between 18 00 and 21 00 utc matched the occluded front positions derived from the concurrently collected surface weather maps from the national oceanic and atmospheric national weather service archives the wrf simulated low wind zone associated with the occluded front and ocean surface wind speed match well with the sar and scatterometer wind retrievals high wind outside the front zone became weaker during the front evolution whereas the width of the occluded frontal zone was contracted laterally analysis of the wrf model derived potential temperature field suggests that the occlusion process occurred below the 800 mb level the structure of the occluded front studied here not only follows the conventional conceptual model and also supports the findings of a novel wrap up conceptual model for an atmospheric frontal occlusion process

pattern and timing of retreat of the last british irish ice sheet during the last glacial the ice sheet that subsumed most of britain ireland and the north sea attained its maximum extent by 27 ka bp and with an ice volume sufficient to raise global sea level by ca 2 5 m when it melted we reconstruct the demise of this british irish ice sheet biis and present palaeo glaciological maps of retreat stages between 27 and 15 ka bp the whole land area was investigated using remote sensing data and we present maps of moraines meltwater channels eskers and drumlins and a methodology of how to interpret and bring them together for the continental shelf numerous large moraines were discovered recording an extensive pattern of retreat stretching from sw ireland to the shetland isles from an integration of this new mapping of glacial geomorphology 26 000 landforms with previously published evidence compiled in the britice database we derive a pattern of retreat for the whole biis we review and compile relevant dates 881 examples that constrain the timing of retreat all data are held within a geographic information system gis and are deciphered to produce a best estimate of the combined pattern and timing of retreat pattern information reveals an ice sheet mainly comprised of a shelf parallel configuration from sw ireland to ne scotland but it spread far enough to the south to incorporate outlying ice domes over wales the lake district and kerry final disintegration was into a number of separate ice caps rather than reduction as a single mass and paradoxically retreat was not always back to high ground by 23 ka bp ice withdrew along its northern boundaries at the same time as the southern margins were expanding including transient ice streaming down the irish sea and advances of lobes in the cheshire basin vale of york and east coast of england ice divides migrated south by 19 ka the ice sheet was in crisis with widespread marine based ice losses particularly in the northern north sea and the irish sea considerable dynamic thinning occurred during this phase final collapse of all marine sectors occurred by 17 ka bp and with most margins beginning to back step onshore disintegration of the north sea ice bridge between britain and norway remains loosely constrained in time but the possibility of catastrophic collapse of this sector is highlighted the north channel and irish sea ice streams had finally cleaved the ice sheet into separate irish and scottish ice sheets by 16 ka bp rates of ice loss were found to vary widely over space and time e g 65 260 km3 per year the role of ice streams and calving losses of marine based sectors are examined retreat rates of up to ca 150 ma 1 were found for some ice stream margins that large parts 2 3 of the biis were marine based drained by ice streams and possibly with fringing ice shelves in places makes it a useful analogue for the west antarctic ice sheet wais this is especially so because the biis deglaciated in response to rising temperatures and a rising sea level driven by melting of other ice masses which are the current forcings that might cause collapse of the wais our reconstruction when viewed from the opposite perspective documents when fresh land became exposed for exploitation by plants animals and man and records for how long such land has been available for soil and geochemical development and ecological succession

reconstruction of glaciation over the past 6 myr from ice borne deposits in the norwegian sea it is well known that a significant intensification of northern hemisphere glaciation occurred 2 5 myr ago in contrast to the much earlier onset 35 myr of glaciation in antarctica1 3 much less is known about the behaviour of the climate before 2 5 myr and it has remained unclear when sizeable glaciers first started to develop in the northern hemisphere here we deduce the history of high northern latitude glaciation over the past 6 myr from records of ice borne deposits in deep sea sediments of the norwegian sea we find that glaciers large enough to reach sea level were present in the norwegian sea area as early as 5 5 myr three million years before the intensification of glaciation at 2 5 myr fluctuations in ice volume can be deduced from the oxygen isotope record but this provides only a global average which may not reflect the history of ice sheet growth in specific regions from a comparison of the oxygen isotope records with the record of ice rafted material we derive an estimate of the relative contributions of southern and northern hemisphere glaciation to global variations in ice volume

a satellite derived classification scheme for rapid maritime cyclogenesis abstract guided by the conjecture that there exist characteristic synoptic scale flow patterns conducive to extratropical cyclogenesis a satellite based classification scheme is proposed to differentiate between various types of rapid maritime cyclogenesis in the western north atlantic region the scheme is derived from signatures in visible and infrared satellite imagery observed prior to and during rapid deepening consideration of the western north atlantic region is motivated by the presence of a relatively dense upstream observational network and by the absence of the direct influence of orography in a maritime environment the focus on rapid development is predicated upon the assumption that the cloud signatures will be more clearly defined than in cases of slower ordinary development examination of satellite imagery for an ensemble of 50 cyclogenesis events that occurred during the 1970s and 1980s 46 of which satisfied the experiment on rapidly intensifying cyclones over the atlantic criterio

precipitation banding in idealized baroclinic waves abstractmoist idealized baroclinic wave simulations show the development of precipitation bands from a zonally uniform initial midlatitude jet for a frictionless lower boundary and with no latent heat release or surface heat and moisture fluxes warm advection is strong and a bent back warm front forms although a narrow vertical velocity maximum forms within the area of synoptic scale ascent near the triple point only a wide warm frontal band forms as surface roughness length increases between simulations to that of an ocean then a land surface warm advection is reduced and the cold front becomes stronger relative to the warm front a separate narrow rainband forms along the cold front which is more intense and farther removed from the wide warm frontal band when roughness length is greater in the simulation with roughness length appropriate to the ocean after the narrow band decays the precipitation becomes oriented along the warm conveyor belt in the warm sector when latent heat release is in

mid pleistocene ice drainage pattern in the norwegian channel imaged by 3d seismic abstract several investigations have shown that a huge late weichselian ice stream flowed along the norwegian channel and deposited thick debris flow deposits at the north sea fan the development of the channel is probably mainly a result of several cycles of ice stream activity during the quaternary a merged 3d seismic image shows a lineated relief pattern interpreted as a uniquely well preserved footprint of a moving ice sheet this deep quaternary horizon corresponds to a slightly irregular reflector on top of a parallel layered seismic sequence seismic tie to the troll core 8903 south of the study area shows that the sequence comprises early middle pleistocene marine sediments the pattern of lineations the seismic stratigraphy as well as the chronostratigraphic investigations of the troll core strongly indicate that the image reflects the initial phase of an extensive middle pleistocene glaciation inferred age ca 0 5 ma prior to the development of a massive norwegian channel ice stream the northwesterly oriented pattern seen in the southeastern part of the study area demonstrates that the ice flowed into the channel mainly from the coastal zone north of bergen farther west various sets of fan shaped lineations partly cross each other showing that the 3d image represents a certain short time window in the northern study area the ice flow was dominantly northwards and directed towards the area below the present shallow maloy plateau there are no indications that the glaciers north of sognefjorden affected the marine ice sheet

bounds on low frequency seismic velocities in partially saturated rocks the most common technique for estimating seismic velocities in rocks with mixed pore fluid saturations is to use gassmann s relations with an effective fluid whose density and compressibility are averages of the individual pore fluid properties this approach is applicable only if the gas oil and brine phases are mixed uniformly at a very small scale so the different wave induced increments of pore pressure in each phase have time to diffuse and equilibrate during a seismic period in contrast saturations that are heterogeneous over scales larger than the characteristic diffusion length i e patchy saturation will always lead to higher seismic velocities than if the same fluids are mixed uniformly at a fine scale critical saturation scales separating uniform from patchy behavior are typically of the order 0 1 1 cm for laboratory measurements and tens of centimeters for field seismic frequencies for low seismic frequencies velocities corresponding to patchy and homogeneous saturations represent a

reconstructing the dynamics of the north west european pleistocene ice sheets abstract the flow lines of the north west european pleistocene ice sheets can be reconstructed with the aid of fabric measurements and glaciotectonic investigations from this there is evidence for a more extensive saalian glaciation of the north sea area than previously assumed with regard to the weichselian different glaciological models can be tested against the field evidence deformable bed and instantaneous glaciation may be partially responsible for the observed phenomena however while at the end of the weichselian there was fast moving ice largely following the course of the baltic sea depression during the weichselian maximum conventional radial ice flow as envisaged by hughes et al 1981 was dominant directional evidence suggests that fast moving baltic ice was present during the late stages of the older and younger saalian glaciations however possibly as a result of isostatic effects it occupied a more southerly position than during the weichselian

a review of the structure and dynamics of upper level frontal zones abstract this article presents a review of upper level fronts with the intent of synthesizing observational and modeling studies into a conceptual and dynamical description of these fronts and their evolution relative to the life cycle of midlatitude baroclinic waves the discussion begins by tracing present day concepts concerning the structure of upper level frontal systems which are based on composite analyses of radiosonde and aircraft data from their origins in the pioneering analyses of upper air data in the 1930s perspectives from scales both smaller and larger than upper level frontal systems are provided respectively by considering the effects of turbulent processes on frontal structure and dynamics and by relating variations in frontal structure to the evolution of the baroclinic waves that provide the dynamical environment for upper level frontogenesis the dynamics of upper level fronts are shown to comprise the interactions between the primary geostrophic and secondary ageostrophic cir

large scale development of the mid norwegian margin during the last 3 million years abstract during the last c 2 7 my large quantities of glacially derived material were transported westwards from the norwegian mainland areas and inner shelf and deposited mainly as prograding sediment wedges into a basin of intermediate depth offshore mid norway the deposits are more than 1000 m thick in extensive areas and are defined as the naust formation in the haltenbanken traenabanken region the shelf edge migrated 100 150 km westwards the narrow more shelf was built out only in the order of 30 50 km mainly due to a steeper pre existing slope dipping towards a much deeper basin in this area the holocene storegga slide as well as older slides displaced slope sediments towards the deeper part of the basin in early naust time the most extensive progradation occurred in the northern area possibly due to the combined effect of land uplift and glaciations the importance of glaciations for the progradation of the more shelf and areas farther south increased through the pleistocene period the norwegian channel ice stream became very important during the last three glaciations and a thick succession of glacigenic debris flows was deposited on the north sea fan more than 400 m of sediments accumulated during the weichselian all the last three glaciations supplied glacial debris beyond the shelf edge the most extensive progradation in the north was in the skjoldryggen region particularly during the elsterian glaciation during ice free periods hemipelagic and contouritic sediments were deposited on the slope such sediments are most common in the storegga slide area where they hosted glide planes beneath the major slides