a 160 k y old record of el nino southern oscillation in marine production and coastal runoff from santa barbara basin california usa a 160 k y old laminated sediment record from the santa barbara basin california analyzed using scanning electron microscope techniques provides a history of interannual variability of marine production and coastal runoff we used backscatter electron imagery to measure the components of the varve these include a terrigenous lamina formed by seasonal runoff from winter rains together with a diatomaceous lamina that records marine production during the spring and early summer spectral analysis of terrigenous and diatomaceous laminae thickness reveals significant periodicities of 3 1 and 8 4 yr in the terrigenous series these are indistinguishable within the frequency resolution of the spectra from significant periodicities of 3 5 and 7 6 yr in the diatomaceous series the 3 1 and 3 5 yr periodicities record el nino modulation of coastal runoff and marine production the 8 4 and 7 6 yr periodicities are consistent with modulation by strong to very strong el nino events this is supported by the results of cross spectral analysis of the terrigenous and diatomaceous records which reveal inverse or antiphase relationships at 3 5 and 7 6 yr our work adds to a body of evidence that suggests that el nino has been a persistent feature of late quaternary climate variability

frontogenesis and the development of secondary wave cyclones in fastex two major mechanisms of frontogenesis deformation and shear are important in frontal wave cyclone development horizontal deformation can suppress the nonlinear wave development using an analytic model bishop and thorpe have shown that large strain rates inhibit any wave slope amplification for real cases this ambient strain can be measured using the vorticity divergence attribution method developed by bishop this technique permits us to confirm the crucial role of such strain on the evolution of cases of wave development during the fronts and atlantic storm track experiment fastex horizontal shear in the presence of an along front thermal gradient is also an important mechanism of frontogenesis using an eady model joly and thorpe have shown that in cases of large along front thermal gradient frontal waves have growth rates smaller than the front itself and thus would not develop the domain independent attribution method developed by bishop is here extended to a geopotential field partition this leads via a nonlinear balance condition to the estimation of the ambient along front potential temperature gradient the role of such an along front potential temperature gradient is discussed as well as the relative contributions of the two frontogenesis mechanisms for the fastex cases

role of orbital forcing in east asian monsoon climates during the last 350 kyr evidence from terrestrial and marine climate proxies from core rc14 99 proxy records of northeast asian precipitation marine pollen and northwest pacific sea surface temperatures marine fauna contain concentrations of variance frequency peaks coincident with those of orbital variations eccentricity obliquity and precession time series of these monitors of various components of the east asian monsoon system are coherent with changing solar insolation and climate boundary conditions ice volume snow cover albedo at 41 and 23 kyr frequencies winter sea surface temperature wsst maxima are in phase with global ice volume minima at all three milankovitch frequencies 100 41 and 23 kyr periods wsst maxima are also linearly related to summer insolation at 30 n lagging radiation maxima by 55 3 5 kyr across the precessional frequency band 23 kyr period our east asian monsoon rainfall indicator cryptomeria reaches highest values immediately following summer insolation maxima during periods of low ice volume interglacials across the eccentricity frequency band 100 kyr period cryptomeria maxima are in phase with ice volume minima at the higher frequency of orbital precession monsoon rainfall lags both summer radiation maxima 125 8 kyr and ice volume minima 60 3 8 kyr whereas much of the variation in northwest pacific wsst can be attributed to summer radiation forcing and changes in global climate mechanisms driving east asian monsoon precipitation are more complex involving other possibly internal factors

new ams dates stratigraphic correlations and decadal climatic cycles for the past 4 ka at lake turkana kenya abstract new ams radiocarbon dates and stratigraphic correlations of 7 piston cores recovered from lake turkana east africa show that the frequency of cyclic variability is greater than previously reported for a single piston core almost 60 new ams dates of various carbonate fractions indicate that large 150 m ostracode carapaces yield the most accurate chronology for the sediment record due to the input of old fine grained carbonate stratigraphic correlations among the cores by carbonate abundance and magnetic susceptibility profiles provide supporting evidence for the ostracode based chronology this chronology refines earlier estimates of sediment accumulation that impacts the recurrence interval of lamination deposition from one lamination every two years to one lamination per year in two north basin cores the record of carbonate content within the north basin of the lake reflect its dilution with terrigenous sediments input from the omo river but direct paleoclimatic interpretations are complicated by lateral migrations of the delta channels with changing lake levels time series analysis of both individual cores and a combined carbonate profile show significant spectral peaks at 1000 76 32 22 18 6 and 11 yr the latter three suggest an important link between the sediments accumulating in lake turkana and global cycles of climatic variability

transient development in confluent and diffluent flow abstract explaining the growth of disturbances superimposed on mean flows is a central problem in meteorology most widely studied models of the development process involve perturbations to shear flows with shear restricted to the meridional direction recently the importance of zonal variation of the mean flow was recognized and the study of shear flows extended to include zonal variation in shear these studies found that the eigenfunctions associated with unstable modes in the simple shear problem are highly sensitive to zonal variation of the mean flow however there also exists another mechanism for development in a zonally inhomogeneous flow field transient growth not associated with exponential instability properly configured perturbations exhibit transient growth in deformation fields associated with regions of confluence and diffluence at rates comparable to development in shear flow in this work analytic solution of the linear initial value problem for the barotropic vorticity equation in de

persistent late pleistocene holocene seasonal upwelling and varves off the coast of california abstract seasonal production of siliceous phytoplankton and a seasonal flux of terrigenous clastic material produced varved sediments along the continental slope off california during the late pleistocene to mid holocene light colored sediment within laminations and in sediment trap samples was deposited during summer upwelling and contains an abundance of the diatoms skeletonema costatum and chaetoceros spp resting spores dark colored sediment deposited in the fall and winter contains abundant thalassiosira pacifica and has more terrigenous material distribution of diatoms in varves shows that seasonal upwelling has persisted along the california coast and has remained strongly seasonal since the late pleistocene

the varve microcosm propagator of cyclic bedding changes in the proportion of seasonal components within varves accumulate over time to produce cyclic bedding a varve couplet is therefore a microcosm of bedding at a larger scale within the same stratigraphic unit cyclic bedding arises from a differing physical response or a phase shifted temporal response to climatic forcing an example from the permian castile formation suggests that the skipping of climatic cycles by the bedding response may be a common occurrence leading to erroneous estimates of the frequency of cyclic bedding seasonal changes that generate cyclic bedding occur in two domains of episodic sedimentation separated by a megathreshold between pelagic and advective environments cumulative changes responsive to seasonality within either domain can produce several types of cyclic bedding over a broad range of frequencies extending into the milankovitch band

sediment cd and mo accumulation in the oxygen minimum zone off western baja california linked to global climate over the past 52 kyr 1 concentrations of organic carbon orgc cadmium cd and molybdenum mo were measured in two sediment cores raised from depths of 430 and 700 m within the oxygen minimum zone omz off southern baja california at a temporal resolution of 0 5 kyr over the past 52 kyr these records are supplemented with diffuse spectral reflectance dsr measurements obtained on board ship soon after collection at a resolution of 0 05 kyr in the core from 700 m depth a component extracted from the dsr data and the three geochemical proxies generally vary in concert with each other and over a wide range 4 22 orgc 1 40 mg kg cd 5 120 mg kg mo intervals of increased orgc cd and mo accumulation generally correspond to warm periods recorded in the oxygen isotopic composition of greenland ice with the exception of the bolling allerod which is only weakly expressed off baja california concentrations of the biogenic proxies are higher in the core from 430 m depth but erratic sediment accumulation before 15 ka precludes dating of the older intervals that are laminated and contain elevated orgc cd and mo concentrations the new data provide further evidence of an intimate teleconnection between global climate and the intensity of the omz and or productivity along the western margin of north america on the basis of a comparison with cd and mo records collected elsewhere in the region we conclude that productivity may actually have varied off southern baja california by no more than a factor of 2 over the past 52 kyr

the influence of transient upper level barotropic growth on the development of baroclinic waves in a previous study of two cyclones within the fronts and atlantic storm track experiment iop11 and iop17 it was shown that upper level barotropic growth dominated the initial phase of the development the cyclones later developed due to baroclinic energy conversion these cyclones resemble petterssen s type b paradigm this contribution presents the dynamics of archetypical type b cyclogenesis by addressing the consequences of upper level barotropic growth before baroclinic cyclone development within the framework of idealized primitive equation simulations localized and finite amplitude upper level pressure perturbations have been designed to represent a variety of amplitudes and horizontal tilts of a localized barotropic trough structure these are added to a zonal jet basic state and it is shown that favourable initial situations similar to the observed cyclones lead to much stronger and faster cyclonic development compared with unfavourable ones the most effective barotropic initial situation without a vertical tilt and considering growth over a time scale of 48 hours is one with a horizontal tilt against the shear of an upper level trough on the cyclonic side of a jet associated with a baroclinic zone

patterns and causes of millennial scale climate change in the pacific northwest during marine isotope stages 2 and 3 abstract a high resolution pollen record from fargher lake washington shows a series of millennial scale changes in vegetation and climate during marine isotope stages mis 3 and 2 a comparison of fargher lake with pollen records from little lake oregon and carp lake washington reveals regional patterns of change during the early part of mis 3 ca 60 000 45 000 cal yr bp fargher and carp lakes indicate transitions between open and closed vegetation and cold dry and warm wet conditions between 45 000 and 27 500 cal yr bp all three records show shifts between low and high elevation taxa that indicate a series of temperature changes these temperature changes are similar to those in the santa barbara basin and may be explained by changes in the strength of the aleutian low during mis 2 27 500 14 000 cal yr bp shifts between wet and dry adapted taxa were most prominent at little lake there is also evidence for two minor warmings mis 2 climate variations do not correlate well with those in the santa barbara basin however precipitation changes in the pacific northwest during mis 2 correlate with evidence of ice sheet surges into the north atlantic and were probably related to variations in the strength and position of the glacial anticyclone and the jet stream

biogenic sedimentation beneath the california current system for the past 30 kyr and its paleoceanographic significance a north south transect of 17 cores was constructed along the eastern boundary of the california current system from 33 to 42 n to investigate the changes in biogenic sedimentation over the past 30 kyr percentages and mass accumulation rates of caco3 corg and biogenic opal were assembled at 500 to 1000 years sample to provide relatively high resolution time space maps reveal a complex pattern of changes that do not follow a simple glacial interglacial two mode model biogenic sedimentation shows responses that are sometimes time transgressive and sometimes coeval and most of the responses show more consistency within a limited geographic area than any temporal consistency reconstructed conditions during late oxygen isotope stage 3 were more like early holocene conditions than any other time during the last 30 kyr coastal upwelling and productivity during oxygen isotope stage 3 were relatively strong along the central california margin but were weak along the northern california margin precipitation increased during the last glacial interval in the central california region and the waters of the southern california margin had relatively low productivity productivity on the southern oregon margin was relatively low at the beginning of the last glacial interval but by about 20 ka productivity in this area significantly increased this change suggests that the center of the divergence of the west wind drift shifted south at this time the end of the last glacial interval was characterized by increased productivity in the southern california margin and increased upwelling along the central california margin but upwelling remained weak along the northern california margin a sudden 300 years decrease in caco3 corg and biogenic opal occurred at 13 ka the changes suggest a major reorientation of the atmospheric circulation in the north pacific and western north america and the establishment of a strong seasonality in the central california region a carbonate preservation event occurred at 10 ka that appears to reflect the uptake of co2 by the terrestrial biosphere as the northern latitudes were reforested following retreat of the glaciers the holocene has been a period of relatively high productivity in the southern california margin relatively strong coastal upwelling along the central california margin relatively weak upwelling along the northern california margin and the northward migration of the divergence zone of the west wind drift

zoophycos cyclicity during the last 425 ka in the northeastern south china sea evidence for monsoon fluctuation at the milankovitch scale in a deep sea piston core covering the last 425 ka from the northeastern south china sea power spectrum analysis of several core data from sediment parameters has been conducted and compared with

sediment geochemical records of productivity and oxygen depletion along the margin of western north america during the past 60 000 years teleconnections with greenland ice and the cariaco basin abstract many sediment records from the margins of the californias alta and baja collected in water depths between 60 and 1200 m contain anoxic intervals laminated sediments that can be correlated with interstadial intervals as defined by the oxygen isotope composition of greenland ice dansgaard oeschger d o cycles these intervals include all or parts of oxygen isotope stage 3 ois3 60 24 cal ka the bolling allerod warm interval b a 15 13 cal ka and the holocene this study uses organic carbon corg and trace element proxies for anoxia and productivity namely elevated concentrations and accumulation rates of molybdenum and cadmium in these laminated sediments to suggest that productivity may be more important than ventilation in producing changes in bottom water oxygen bwo conditions on open highly productive continental margins the main conclusion from these proxies is that during the last glacial interval lgi 24 15 cal ka and the younger dryas cold interval yd 13 11 6 cal ka productivity was lower and bwo levels were higher than during ois3 the b a and the holocene on all margins of the californias the corg and trace element profiles in the lgi b a holocene transition in the cariaco basin on the margin of northern venezuela are remarkably similar to those in the transition on the northern california margin correlation between d o cycles in greenland ice with gray scale measurements in varved sediments in the cariaco basin also is well established synchronous climate driven changes as recorded in the sediments on the margins of the californias sediments from the cariaco basin and in the gisp 2 greenland ice core support the hypothesis that changes in atmospheric dynamics played a major role in abrupt climate change during the last 60 ka millennial scale cycles in productivity and oxygen depletion on the margins of the californias demonstrate that the california current system was poised at a threshold whereby perturbations of atmospheric circulation produced rapid changes in circulation in the eastern north pacific ocean it is likely that the pacific and atlantic oceans were linked through the atmosphere warmer air temperatures during interstadials would have strengthened hadley and walker circulations which in turn would have strengthened the subtropical high pressure systems in both the north pacific and the north atlantic producing increased rainfall over the cariaco basin and increased upwelling along the margins of the californias

dynamical characterization of the fastex cyclogenesis cases summary a series of diagnostics based on the automatic tracking of cyclones is applied to the 25 life cycles captured during the fastex field experiment the tracking enables a setting of the various cases into a common frame of reference that moves with the system time filtering is used to further separate the events into a basic state and perturbations information is obtained on environmental properties such as strain or baroclinicity combining these diagnostics it is shown that instability mechanisms based on the existence of potential vorticity strips or the control of these instabilities by deformation may be involved in the initial genesis of a number of cases but do not seem to characterize specific types nor to determine a systematic behaviour on the other hand it is shown that rapid deepening phases leading eastern atlantic systems to their maximum amplitude happens suddenly and at the same time as crossing the jet stream even in the absence of a clear additional upper level feature for cold air systems development means meeting a diffluent zone this is unlike the american east coast systems that are associated with an exit entrance complex another remarkable feature is the generation of a frontal waveas a re sult of the parent vorticity maximum being apparently stretched and split this has occurred in 25 of cases a number of other properties of the fastex cases are shown such as several occurrences of large

ichnofabrics of a pleistocene slope succession new jersey margin relations to climate and sea level dynamics abstract trace fossil and sedimentologic data were collected at 10 cm intervals throughout a virtually continuous 520 m thick upper pleistocene siliciclastic succession recovered at odp site 1073 new jersey margin these data were examined in the context of isotopic seismic and palynologic proxies to document depositional and ichnologic responses to quaternary climate and sea level dynamics in an upper slope setting two broad texturally defined sedimentary facies assemblages are recognized the clay rich assemblage reflects relatively rapid deposition in part from turbidity currents and suspended plumes and appears to be linked to cooler sea level fall and lowstand phases the sand rich assemblage reflects overall slower sedimentation by offshelf spillover and periodic winnowing and erosion under the influence of contour and other bottom currents during warmer transgressive highstand phases facies of the sand rich assemblage muds sandy muds muddy sands and sands are completely bioturbated and are characterized by high densities of biogenic structures including distinct burrow forms in contrast the clay rich assemblage includes facies that exhibit limited biogenic disruption laminated clay silty clay and graded silt or fine sand to clay couplets and on the whole is characterized by lower densities of biogenic structures most of which are diffuse burrow mottles these ichnofabric trends reflect changes in ecological and taphonomic parameters e g substrate stability and consistency residence time of sediments in the benthic boundary layer and degree of inter and intrabed textural variability many of which were governed by variations in sedimentation rate as mediated by glacio eustacy recurring identifiable ichnofossils are most common in facies of the sand rich assemblage in the upper half of the pleistocene succession finer grained components of this assemblage e g muds and sandy muds representing quieter phases of highstand deposition are characterized by a low diversity distal cruziana ichnofacies assemblage dominated by schaubcylindrichnus and phycosiphon anconichnus both of which represent the work of deposit feeding worms narrow facies transitions that correspond to phases of rapid transgression are marked by occurrences of thalassinoides these crustacean burrow systems were excavated in coarser grained higher energy facies sands and muddy sands and in closely associated firmground substrates produced by exhumation of consolidated muds by bottom currents and or mass wasting processes the association of firmground ichnofabrics with marine flooding events in an upper slope setting demonstrates that the sequence stratigraphic utility of the glossifungites ichnofacies extends beyond shelf depositional sequences to deeper water deposits the distribution of texturally defined facies and general ichnofabric parameters e g degree of bioturbation appears to respond to glacio eustatic cycles through the entire pleistocene record however the schaubcylindrichnus phycosiphon assemblage and thalassinoides are rare or absent altogether in the lower half of the succession indicating that biological responses to and the ichnologic record of climate and sea level dynamics may be strongly dependent on margin physiographic and bathymetric evolution

evidence for a stronger oxygen minimum zone off central california during late pleistocene to early holocene of 31 deep sea cores collected along the central california continental slope 18 have distinctly laminated sediment at depth but none have laminations in the top few centimetres the cores with laminated facies are restricted to water depths between 508 and 1508 m but not all cores taken from this depth interval have laminated facies 14 c dates yield an extrapolated age of 4700 b p for the top of the uppermost laminated unit comparisons of the diatom flora in the laminated couplets with diatom floras in a 13 month sediment trap record suggest that the laminations are varvelike couplets of seasonal sedimentation the laminated facies represent a period from the last global deglaciation to early holocene when the oxygen minimum zone along the northeastern pacific ocean was stronger than at present a stronger oxygen minimum zone during this time is inferred to be the result of intensified upwelling

warm water mollusc assemblages from northern chile mejillones peninsula new evidence for permanent el nino like conditions during pliocene warmth although results have been controversial understanding the tropical pacific climatic state during the pliocene warm interval c 4 5 3 0 ma is crucial if insight is to be gained into the dynamic processes of present and future global warming in the multi proxy effort to reconstruct ancient climates a critical role can be played by palaeoclimatic evidence provided by the spatial and temporal distribution of temperature sensitive marine molluscs shallow water strata of the mejillones peninsula northern chile 23 s contain dense faunal assemblages in which molluscs exclusive to or characteristic of pliocene deposits chlamys simpsoni chlamys vidali chorus blainvillei concholepas nodosa fusinus remondi herminespina mirabilis coexist with surprisingly abundant and varied populations of extant warm water species bulla punctulata cerithium stercusmuscarum olivella sp turbo cf fluctuosus anomia peruviana argopecten ventricosus donax peruvianus dosinia ponderosa mexicardia procera undulostrea megodon most of which have their current southern zoogeographical limit at 6 s these tropical elements are reliable indicators of nearshore marine conditions and their abundant occurrence implies that sea surface temperatures sst along the northern chile coast were at least 2 c warmer in the mid pliocene than at present and that these very different conditions lasted long enough to allow stable colonization of the area such a significantly warmer sst pattern strongly resembles general climatic conditions accompanying modern el nino events when warm tropical waters propagate southward along the western margin of south america this supports the existence in this area of persistently el nino like conditions during the mid pliocene

holocene glacier and deep water dynamics adelie land region east antarctica abstract this study presents a high resolution multi proxy investigation of sediment core md03 2601 and documents major glacier oscillations and deep water activity during the holocene in the adelie land region east antarctica a comparison with surface ocean conditions reveals synchronous changes of glaciers sea ice and deep water formation at milankovitch and sub milankovitch time scales we report 1 a deglaciation of the adelie land continental shelf from 11 to 8 5 cal ka bp which occurred in two phases of effective glacier grounding line retreat at 10 6 and 9 cal ka bp associated with active deep water formation 2 a rapid glacier and sea ice readvance centred around 7 7 cal ka bp and 3 five rapid expansions of the glacier sea ice systems during the mid to late holocene associated to a long term increase of deep water formation at milankovich time scales we show that the precessionnal component of insolation at high and low latitudes explains the major trend of the glacier sea ice ocean system throughout the holocene in the adelie land region in addition the orbitally forced seasonality seems to control the coastal deep water formation via the sea ice ocean coupling which could lead to opposite patterns between north and south high latitudes during the mid to late holocene at sub milankovitch time scales there are eight events of glacier sea ice retreat and expansion that occurred during atmospheric cooling events over east antarctica comparisons of our results with other peri antarctic records and model simulations from high southern latitudes may suggest that our interpretation on glacier sea ice ocean interactions and their holocene evolutions reflect a more global antarctic holocene pattern

four dimensional variational analyses of fastex situations using special observations this paper focuses on intensive observation period 17 of the fronts and atlantic storm track experiment fastex the fastex special soundings obtained during that period are added to the conventional dataset and assimilated with a 4 dimensional variational 4d var scheme under development at meteo france results show a consistent use of the high density fastex ship soundings by the 4d var formulation and an improvement brought by this new scheme over 3d var when using only the vertical profiles synchronous with synoptic time the application of the 4d var analysis to dropsondes launched by a system relative flight designed by the joint centre for mesoscale meteorology also produces a fine scale description of sub structures of the mature system

pelletal structures in peruvian upwelling sediments late quaternary sediments from the peru upwelling zone have been investigated using backscattered electron imagery the dysaerobic to anaerobic conditions which persist within the strong oxygen minimum zone intersecting the shelf and upper slope sediments have resulted in the preservation of a wide range of microscopic fine structure relating to biological activity two forms of pelletal structures are present pellets and aggregate structures 1 pellets are oval in cross section with a mean diameter of 610 m and sharp boundaries three common pellet types have been identified a crushed diatom and clay pellets b intact diatom pellets and c silt pellets 2 aggregate structures are smaller than pellets with a mean diameter of 360 m they have indistinct boundaries and may be composed either of pure diatom ooze or a mix of clay silt and diatoms the size shape and mode of occurrence of aggregate structures suggest that they are the product of a meiofauna redistributing the topmost sediment during periods of very slight increases in oxygen most of the crushed diatom clay pellets and intact diatom pellets are probably also the product of a surficial deposit feeding fauna tolerant of low dissolved oxygen levels such as polychaete worms silt pellets may record the chamber building activities of agglutinating foraminifera

frontal wave development by interaction between a front and a cyclone application to fastex iop 17 the way new cyclones appear along a baroclinic zone is central to the problem of the prediction of mid latitude cyclones a new barotropic mechanism for frontal wave development is proposed in the present paper the ingredients are a frontal environment characterized by horizontal wind shear and a finite amplitude initial wind perturbation orthogonal to the main deformation axis associated with the front it is found that the initial wind perturbation can be provided by a low level vortex maximum located north westward with respect to the position of the new cyclone interactions between these synoptic features are documented using local energetics the theory is only valid at the very early stage of development after a few hours the main growing phase which is mostly baroclinic will take place a wide set of experiments is performed in order to find the preferred location of the vortex at the initial time in the frame of the barotropic vorticity equation the result is found to be consistent with the fronts and atlantic storm track experiment case studied in this paper frontogenetic forcing provided by a deformation field does not inhibit the perturbation amplification it is also found that the impact of the vortex is significantly larger than potential instabilities developing along the front where the unstable feature is defined as the most unstable singular vector copyright 2004 royal meteorological society

the role of the environmental flow in the development of secondary frontal cyclones the impact of the environmental flow on the development of secondary frontal cyclones is investigated several case studies are examined as examples of secondary frontal cyclone events observed in the north atlantic western europe sector a simple measure of growth is defined to chart their development the vorticity attribution technique of bishop is utilized to calculate the action of the large scale environmental flow on the fronts in particular the environmental along front stretching shown to be important in theoretical models of frontal instabilities is calculated the role of the environmental deformation appears to be crucial as part of a baroclinic life cycle stretching deformation acts to build up a front but suppress along front waves if the stretching rate diminishes barotropic instabilities may then break out diagnostics are examined to try to ascertain the growth mechanisms at work in each frontal cyclone case a range of values for the commonly prescribed deformation frontogenesis and shearing frontogenesis parameters are calculated

non annual laminations and expansion of anoxic basin floor conditions in santa monica basin california borderland over the past four centuries sediments from box cores in the deep portion of santa monica basin have been examined by x radiography and the upper 10 20 cm are characterized by laminations 1 5 mm in thickness age dating of 9 cores by 210pb analysis has shown that accumulation rates on the central basin floor have been remarkably constant during the past century averaging 16 0 0 4 mg cm2 yr densitometer analysis of the x radiography films from 7 cores and spectral analysis of the resulting time series indicates that most lamination couplets have a periodicity in the 3 7 year range a range matching that of the el nino southern oscillation periodicity the median periodicity appears to have decreased slightly during the past 3 centuries from 7 0 years during 200 300 yrs b p to 5 2 yrs during 0 100 yrs b p this trend could be due to a decreasing sedimentation rate an increasing forcing frequency or an increasingly faithful response of the basin in more recent years multiple processes have contributed to creation of the laminations in santa monica basin the principal factors appear to be 1 variations in porosity due to the relative abundance of organic filaments probably formed by beggiatoa mats and 2 compositional variations that reflect variations in carbonate lithogenous ratios and in grain size both of these are expected to respond to enso events the presence of near anoxic bottom waters has prevented bioturbation permitting laminations to be preserved basin bottom waters became nearly anoxic about 350 years ago at the onset of warming as the little ice age waned expansion of the near anoxic area during the past century may have been augmented by 20th century anthropogenic effects the style of these non annual laminations in santa monica basin matches that of the annual laminations in the adjacent santa barbara basin and demonstrates the need for caution in interpreting all laminations as representing annual varves

expression of seasonal and enso forcing in climatic variability at lower than enso frequencies evidence from pleistocene marine varves off california abstract upper pleistocene marine sediments along the upper continental slope off northern and central california contain alternations of varved and bioturbated sediments and associated changes in biota and sediment composition these alternations can be related to conditions that accompany el nino and anti el nino enso circulation anti el nino conditions are characterized by increased upwelling and productivity and by low concentrations of dissolved oxygen in the oxygen minimum zone that resulted in varve preservation el nino conditions are characterized by little or no upwelling low productivity and higher concentrations of dissolved oxygen that resulted in zones of bioturbation alternations of varves and zones of bioturbation that range from decades to millennia occur through the upper pleistocene section the inferred long term alternations in el nino and anti el nino conditions appear to be a re expression of enso s primary 3 7 year cycle decadal to millennial cycles of productivity associated with el nino and anti el nino conditions may have served as a carbon pump and transferred atmospheric co 2 to the marine reservoir changes in sediment composition and organisms associated with el nino or anti el nino conditions can be related to both seasonal and enso phenomena expression of these changes at lower than enso frequencies may be partly explained by adding the effects of seasonal variability to effects produced by a self oscillating enso system however deterministic mechanisms including solar modulation of enso may also contribute to long term alternations of el nino and anti el nino conditions

role of the low frequency deformation field on the explosive growth of extratropical cyclones at the jet exit part i barotropic critical region abstract by using new theoretical results on perturbation growth in spatially and temporally complex quasigeostrophic flows this paper investigates the role of the large scale deformation field on extratropical cyclones and especially on their explosive growth in the jet exit region theoretical ideas are tested by decomposing the atmospheric flow into a high and a low frequency part and by analyzing four dimensional variational data assimilation 4dvar reanalysis data of the fronts and atlantic storm track experiment fastex during february 1997 as well as reanalysis data for the end of december 1999 regions where the low frequency deformation magnitude is greater than the absolute value of the low frequency vorticity are shown to correspond to regions where synoptic disturbances at the same level tend to be located these regions in the upper troposphere are intrinsically related to the horizontal inhomogeneities of the low frequency large scale upper tropospheric jet but cannot be detected by look

coastal upwelling in the california current system abstract coastal upwelling in the california current system has been the subject of large scale studies off california and baja california and of small scale studies off oregon recent studies of the winds along the entire coast from 25 n to 50 n indicate that there are significant along shore variations in the strength of coastal upwelling which are reflected in the observed temperature distribution active upwelling appears to be restricted to a narrow coastal band about 10 25 km wide along the entire coast but the region influenced by coastal upwelling may be much wider intensive observations of the upwelling zone during summer off oregon show the presence of a southward coastal jet at the surface a mean vertical shear a poleward undercurrent along the bottom and persistently sloping isopycnals over the continental shelf most of the upwelling there occurs during relatively short periods several days long of upwelling favorable winds during the upwelling season off oregon the offshore ekman transport is carried by the surface ekman layer and the onshore return flow occurs through a quasi geostrophic interior it is not known whether the structure and dynamics observed off oregon are typical of the upwelling zone along the entire coast though some of the same features have been observed off baja california current and future research will eventually show whether the oregon results are also applicable in the region of persistently strong upwelling favorable winds off northern california and in the region of complex bathymetry off central and southern california

peru coastal currents during el nino 1976 and 1982 year long measurements of subsurface current and temperature on peru9s continental shelf included the onset of el nino in 1976 and 1982 the peru coastal undercurrent more than doubled in speed and advected anomalously warm water poleward el nino began in different seasons in 1976 and 1982 but the current and temperature responses were very similar acceleration of poleward flow at 10 s occurred several days after sea level rose at the galapagos islands in october 1982 suggesting the onset of el nino propagated as a kelvin wave

facies analysis and correlation of high order sequences in middle outer ramp successions variations in exported carbonate on basin wide δ13ccarb kimmeridgian ne spain carbonate mud that accumulated in the deep parts of a late kimmeridgian carbonate ramp iberian basin ne spain was partly derived by resedimentation from shallow water production areas high frequency sea level changes probably driven by climatic changes in tune with precession and short eccentricity cycles affected carbonate production and the amount of exported sediment facies analysis and correlation of three outcrops located in middle and outer ramp settings allows a comparison of high order sequences bundles of beds and sets of bundles across a ramp transect and an assessment of the carbonate factory analysis of the storm deposits found in middle ramp settings identifies deepening to shallowing high frequency cycles based on the level of exported carbonate in outer ramp areas many of the bundles exhibit a thinning trend indicating a progressive decrease of carbonate production and hence carbonate export during periods of high frequency sea level rise 13ccarb values show a gradual increase through the studied long term transgressive interval ranging from 1 5 to 2 8 within this long term evolutionary trend short term 13ccarb fluctuations occur that correspond with some of the high order cycles defined from sedimentary facies analysis these short term 13ccarb shifts are interpreted as shifts in carbonate export from shallow reef regions to the outer ramp a consequence of this study is that variation in 13ccarb can be used for correlation in outer ramp successions at least on a basin wide scale

a 4d var re analysis of fastex a complete re analysis of the fronts and atlantic storm track experiment 5 january 27 february 1997 is performed it provides a reference description of the life cycle of an ensemble of cyclogeneses over the north atlantic many aspects make this re analysis noteworthy in particular the fastex period is characterized by an exceptional increase in the number of dropsoundings or radiosoundings concentrated on the storm track another striking point of the re analysis is the use of a four dimensional variational 4d var assimilation scheme on such a long period associated with the french arpege action des recherche petite echelle et grand echelle global stretched model that allows a locally high resolution in the area where dense networks of dropsondes were deployed a twin re analysis with the same characteristics but without any fastex data is also performed it shows that the impact of the special fastex data is quite noticeable in the resulting analyses and is lower but still perceptible in the associated short range forecasts 6 h 36 h the impact of fastex observations on a particular fastex case is also shown copyright 2003 royal meteorological society

frontal wave stability during moist deformation frontogenesis part i linear wave dynamics abstract it has been shown that lower tropospheric potential vorticity zones formed during moist deformation frontogenesis will support growing waves if at some time the frontogenesis ceases in this paper the ways in which these waves are affected by the frontogenetic process are identified observations show that fronts in the eastern atlantic commonly feature saturated ascent regions characterized by zero moist potential vorticity furthermore in many cases the horizontal temperature gradient in the lowest one to two kilometers of the atmosphere is rather weak these features are incorporated in an analytical archetype the dynamical implications of saturated ascent in conditions of zero moist potential vorticity are represented in the model by assuming that adiabatic temperature changes are precisely balanced by diabatic tendencies the observed small temperature gradient at low levels is represented in the model by taking it to be zero in the lowest two kilometers consequently the forcing of the

secondary cyclogenesis the initiation phase of a frontal wave observed over the eastern atlantic the initiation phase of a secondary frontal wave in the wake of a primary cyclogenesis event over the atlantic is documented north of the trailing surface cold front and south west of the primary cyclone an intense upper level jet generates a direct and transverse ageostrophic circulation in its entrance region evidence is shown for two conflicting roles of this circulation first stabilization of the front through frontogenetic cross frontal low level convergence and second an increase of the potential for instability of the front through diabatic e g latent heat release potential vorticity pv redistribution in the upward branch of the circulation following saturation of the primary cyclogenesis and the associated along front north eastwards shift of the upper level jet the low level branch of the ageostrophic circulation behaves like a zipper closing on the front while in the upward branch an anomalous strip of pv builds along the cold front isentropic pv maps show that parcles of stratospheric origin embedded in the downward branch of the ageostrophic circulation a tropopause fold may have ended in the vicinity of the strip of anomalous low level pv perhaps contributing to an increase in the potential for instability of the surface front using the domain independent attribution method of bishop it is shown that the frontal wave forms on a part of the cold front where first the along front stretching rate due to the environmental flow decays below the critical threshold value 0 6 10 5 s 1 prescribed by theoretical studies and second the across front frontogenetic component due to the ageostrophic circulation decays this is consistent with semi geostrophic theory where the cross frontal convergence and the stretching deformation are linked through the sawyer eliassen equation results add to other recent observational findings that the potential for instability the evolving environmental flow and the induced ageostrophic convergence each have a crucial role in differentiating between frontal waves that will grow and those that will be suppressed

distribution of biogenic silica and quartz in recent deep sea sediments all available quartz and biogenic silica concentrations from deep sea surface sediments were intercalibrated plotted and contoured on a calcium carbonate free basis the maps show highest concentrations of biogenic silica opal along the west african coast along equatorial divergences in all oceans and at the polar front in the southern indian ocean these are all areas where upwelling is strong and there is high biological productivity quartz in pelagic sediments deposited far from land is generally eolian in origin its distribution reflects dominant wind systems in the pacific but in much of the atlantic and indian oceans the distribution pattern is strongly modified by turbidite deposition and bottom current processes

climatically induced lake level changes at lake van turkey during the pleistocene holocene transition sediment core k10 from lake van eastern turkey provides a continuous varve record back to 14 570 calendar years b p before present 1950 the longest unbroken and non floating lake varve sequence yet described the underlying sediment is unvarved and hard changes in the aragonite calcite ratio the presence of protodolomite and magnesite in certain profile sections the annual record of the sedimentation rate the water content of the sediment the concentrations of organic carbon and opal and the texture of the sediments from this core provide a record of the lake level history the new chronology enabled us to redate the old pollen profile van zeist and woldring 1978a b and to establish an accurate timescale for the reconstructed lake level change carbon 14 dates show that the highest lake terrace corresponds to high lake level at around 19 000 years b p during the last glacial 70 m above its present level before 15 000 years b p the lake must have been completely dry marking a reduction of lake level by 500 m in maximum 4000 years beginning at 14 600 years b p and ending at 12 040 years b p the lake level recovered by 250 m to fall again during the next 1400 years by 10 600 years b p the lake began to rise and reached following another regression between 9000 and 8100 years b p the holocene highstand by about 7500 years b p dropping to today s level at about 3000 years b p

early holocene decadal scale ocean variability recorded in gulf of california laminated sediments scanning electron microscope examination of holocene laminated sediment from guaymas basin gulf of california resolves up to five depositional events per year each lamina sublamina of an early holocene section of continuously laminated sediment was recorded from backscattered electron imagery photomosaic analysis diatom mat laminae composed predominantly of thalassiothrix longissima are associated with early winter mixed diatom flora laminae mats are probably brought into the gulf with pacific water during the summer concentrated at the surface or at the pycnocline and then rapidly deposited in the early winter as water column stratification breaks down time series analysis of one 300 year section from piston core jpc56 revealed significant periodicities in the deposition of mat laminae at 50 years 11 years and 22 24 years an 50 year cycle in fish populations has been related to changing north pacific ocean atmosphere circulation these pacific wide changes in circulation affect the currents dominant at the mouth of the gulf when the california current is dominant fewer diatom mats are imported into the gulf and when the north equatorial pacific gyre is dominant more are imported the 11 year 22 to 24 year and 50 year cycles are all suggested to be influenced by solar cycles

modern and palaeo oceanographic environments under benguela upwelling cells off southern namibia averaged benthic physical and chemical and key microfaunal ostracoda parameters of the bottom waters and substrate allow a ranking of the intensity of upwelling in the modern cells off southwestern africa b1 b6 b1 namib cell temperature salinity dissolved oxygen total organic matter 10 3 c 34 94 1 2 ml l 6 2 palmoconcha walvisbaiensis cytherella namibensis garciaella knysnaensis robusta and neocaudites lordi b2 walvis cell 11 0 c 35 00 1 0 ml l 9 2 palmoconcha walvisbaiensis cytherella namibensis garciaella knysnaensis robusta buntonia rogersi neocaudites lordi and ruggieria cytheropteroides leeward side only b3 luderitz cell 9 1 c 34 77 1 8 ml l 6 3 palmoconcha walvisbaiensis cytherella namibensis incongruellina venusta kuiperiana angulata and ruggieria cytheropteroides leeward side only b4 namaqua cell 10 0 c 34 82 2 4 ml l 3 1 pseudokeijella lepralioides and ruggieria cytheropteroides b5 columbine cell 8 3 c 34 70 3 1 ml l 3 9 ruggieria cytheropteroides pseudokeijella lepralioides poseidonamicus panopsus and ambostracon a flabellicostata b6 peninsula cell 8 9 c 34 63 3 6 ml l 1 9 pseudokeijella lepralioides ambostracon a keeleri cytherella dromedaria neocytherideis boomeri xestoleberis africana neocaudites osseus coquimba birchi and urocythereis arcana pleistocene palaeo upwelling characteristics of the shelf north west of luderitz are investigated by analysing the ostracod faunas sediment textures and mineralogy of three large volume gravity cores q mode factor analyses using previously published transfer functions allow predictions for benthic environmental parameters during the late pleistocene the area experienced less intense upwelling and lower primary productivity than at present in an environment equated with a modified peninsula cell b6 b7 cell 9 6 c 34 73 3 2 ml l 3 9 neocaudites lordi ambostracon a keeleri bairdoppilata simplex paracypris lacrimata parakrithella simpsoni xestoleberis hartmanni ruggieria cytheropteroides and pseudokeijella lepralioides in middle and early pleistocene late pliocene times the core sites lay closer inshore adjacent to evaporite halite and authigenic phosphorite rich lagoons with a high intensity upwelling walvis like cell b1 to the north west and a low intensity upwelling cell b7 to the south

the upper jurassic boulder beds and related deposits a fault controlled submarine slope ne scotland during the late jurassic kimmeridgian rifting in the north sea large scale normal faults developed to form relatively deep marine basins the north western margin of one of these basins defined by the helmsdale fault is described to show the nature of sedimentation associated with a submarine fault scarp subsidence to the se of the helmsdale fault led to a fault scarp down which various sediment mass flows moved including debris flow rockfall high and low concentration turbidity currents and possible storm surge wash over deposits redeposition by soft sediment sliding was important as a slope accretion process deep channels were incised into the slope and infilled by coarse grained elastics contemporaneous small scale submarine fans located farther off in the present north sea may have developed as a result of slope bypassing sediment flows down such channels the succession is characterized by extreme sediment heterogeneity compared to many deep water environments and it may be part of an ancient fan delta the main influences upon slope accretion were the synsedimentary movements on the helmsdale fault and the nature of the available sediment input such that the succession represents structurally controlled and sedimentologically modified slope development

multiple potential vorticity inversions in two fastex cyclones this paper investigates pre existing synoptic scale disturbances responsible for cyclogenesis using the manipulation of initial conditions through quasi geostrophic potential vorticity qgpv and its inversion the use of a qgpv inversion together with a t63 model allows us to study the sensitivity of some fastex events to several qgpv patterns present within the analysis it has been found that ertel potential vorticity modifications of the analysis are preserved by the dynamical initialization process the qgpv inversion method is applied to cyclones occurring in intensive observation periods iops 11 and 12 of fastex fronts and atlantic storm track experiment to demonstrate which potential vorticity anomalies present within the atmosphere prior to the development are involved in the cyclogenesis the choice of the boundary condition when an upper level precursor is removed from the initial conditions has little impact on the cyclone development the linear interactions advection deformation of the anomaly by its environment and downstream development between these upper level precursors and the surrounding flow dominate the dynamics of iop1 1 cyclone development whereas nonlinear processes are particularly strong in the iop12 case the cyclone development is only weakly sensitive to low level initial structures unless they are shaped like adjoint model sensitivities collocation with another shape has little influence on the development

frontal instability generated by tropospheric potential vorticity anomalies the development of secondary disturbances on a two dimensional front is described using a linear stability analysis a two stage process is envisaged in which first strong frontogenesis produces condensation at the front this leads to the generation of a lower tropospheric zone of high potential vorticity pv lying along the front as frontogenesis weakens the second stage is entered in which an essentially steady front is susceptible to the growth of linear normal modes along the front owing to the existence of the pv anomaly or equivalently the frontal rainband thus for a typical band of width 160 km a frontal wave of some 800 km is produced with a growth rate of about 1 day 1 the dynamics of these modes is examined by considering both the realistic frontal flow as well as idealized strips of pv anomalies the idealized case is potentially applicable to a variety of meteorological situations such as upper jet streaks useful insight is gained from an analysis of the energetics of the modes this shows that for narrow frontal pv anomalies the waves main energy source is the basic kinetic energy and further they have a negative vertical heat flux recent observations suggest that frontal waves are indeed characterized by such a heat flux as most frontal zones involve significant condensation and therefore are likely to exhibit a lower tropospheric pv maximum it is stressed that studies of frontal waves need to include this aspect of the frontal structure

bioturbated oxygenation event beds in siliceous facies monterey formation miocene california abstract predominatly laminated marine diatomaceous sequences deposited in oxygen deficient neogene basins typically contain bioturbated intervals that reflect episodes of improved benthic oxygenation excellent exposures of the siliceous facies of the miocene monterey formation near lompoc central california provided an opportunity to assess the ichnology and sedimentology of 200 such event beds in their general paleogeographic paleoclimatic and sea level context and hence to evaluate the character and causes of associated oxygenation episodes four recurring event bed types type i iv are distinguished on the basis of ichnologic characteristics these types fall into two general groups delineated on the basis of sedimentologic attributes primarily texture group 1 beds type i only have 1 homogeneous bioturbate primary strata that are more clastic rich and much coarser than surrounding laminated diatomites and 2 vertically extensive piped zones characterized by firmground thalassinoides paradoxicus glossifungites ichnofacies these characteristics indicate that group 1 events involve coincident increases in bottom current intensity clastic input and benthic oxygenation some group 1 beds may be the product of turbidity current transport of sediments trauma resistant crustaceans and allochtonous waters however most group 1 beds more likely record climate and sea level mediated migratio of incipient bank top conditions down the flank of a submergent topographic high group 2 beds types ii iii and iv are characterized by primary strata that are only slightly coarser and more clastic rich than surrounding laminites ichnofabrics and trace fossil assemblages which are dominated by burrows of deposit feeders thalassinoides suevicus meniscate backfilled structures and chondrites reflect normal softground substrates and quiet water pelagic deposition zoophycos ichnofacies differences in ichnologic parameters bed thickness adn presence diversity size and vertical extent of discrete burrows in primary strata and or piped zones among the bed types within this group reflect differences in magnitude duration and to a lesser extent frequency of oxygenationepisodes coincident increases in oxygenation and clastic content recorded by group 2 beds are attributed to e1 nino like climatic events gross temporal patterns in the intensity and frequency of these climatic events appear to be linked to the phases of a third order sea level cycle whereas shorter term variations 100 120 ka may have been mediated by milankovitch cyclicity relationships established between bioturbation events and relative water depth are of potential use in reconstructing basin paleogeography and or recognizing the signal of sea level change in the monterey formation and other neogene siliceous sequences

can the greenland climatic jumps be identified in records from ocean and land sharp jumps in climate punctuate the records from borings in the greenland ice cap during the time interval 60 000 to about 20 000 yr ago rapid fluctuations are also seen in foraminifera records for cores from the northern atlantic and in a pollen record from a core from a bog in the vosges mountains in france in this paper we present a new radiocarbon chronology for northern atlantic deep sea core v23 81 which permits comparison with the radiocarbon dated vosges mountains pollen record because of the lack of a 14c chronology for the greenland ice record and of distortions peculiar to each of the three records it is not yet possible to say whether or not the events are genetically related

millennial scale climate origins for stratification in cambrian and devonian deep water rhythmites western usa abstract basinal facies of the middle cambrian marjum formation western utah and middle devonian denay limestone central nevada are characterized by thin rhythmically interbedded limestone and marl layers deep water rhythmites limestone layers average thickness range of 4 3 5 5 cm are composed of laminated to massive pelleted lime mudstone marl layers average thickness range of 0 7 1 7 cm are characterized by laminated argillaceous dolomitic mudstone the absence of current or wave reworked features paucity of bioturbation and skeletal fossils stratigraphic relationships with adjacent facies and the dark color indicate that limestone and marl layers in both rhythmite successions were deposited in quiet dysaerobic waters below storm wave base both limestone and marl layers are composed of submillimeter thick graded laminae which represent discrete depositional events from dilute density currents generated by high frequency storms or distal turbidity currents fluctuations in primary pelagic productivity cannot account for variations in carbonate influx because calcareous microfossils did not evolve until the mesozoic instead the rhythmic interbedding is interpreted to reflect climatically controlled variations in fluvial and or eolian influx or changes in marine currents storm or distal turbidity currents which transported shallow platform derived carbonate material into the deep water region spectral analysis of carbonate time series were compared to lithologic rank series and particularly for the middle cambrian rhythmites were found to be statistically indistinguishable the durations of significant spectral peaks were estimated from calculating the average sedimentation rates from the two biostratigraphically controlled stratigraphic sections these rates range between 4 3 4 1 cm k y and 21 2 29 2 cm k y for the cambrian and 3 6 1 8 cm k y to 5 1 7 4 cm k y for the middle devonian application of these sedimentation rates to the marjum couplets suggests that individual couplets represent between 190 2100 years of time the denay couplets represent 800 1900 years the good agreement between empirical holocene hemipelagic sedimentation rates and the sedimentologic evidence of relatively high depositional rates for the paleozoic rhythmites supports this millennial scale interpretation these results combined with that from previous work in paleozoic evaporite and carbonate successions suggest that millennial scale paleoclimatic variations affected marine and marginal marine sedimentation as far back in time as the cambrian millennial scale climatic change appears to be a permanent feature affecting the oceans and atmosphere and is apparently largely unaffected by major changes in phanerozoic paleogeography tectonics and atmospheric composition

fastex iop17 cyclone introductory synoptic study with field data this paper introduces the study of the early development phase of the iop17 frontal cyclone of the fastex field experiment fronts and atlantic storm track experiment with the support of observations from fastex observing platforms a synoptic description highlights the development of mesoscale features of interest in the operational meteo france arpege action de recherche petite echelle grand echelle analysis cycle i e cloud head dry wedge and upper level jet outflow a discussion attempts to isolate two significant differences of the present cyclone life cycle compared with previous well known conceptual models of maritime cyclone life cycles i the indirect role of an upper level precursor in triggering the surface low ii the existence of a diabatic regime taking over from the baroclinic development to sustain the deepening rate of the cyclone these two mechanisms are the subject of two companion papers

relationships between stylolites and cementation in sandstone reservoirs examples from the north sea u k and east greenland abstract the reservoir potential of hydrocarbon sandstone reservoirs may be significantly reduced by compartmentation as a result of the development of stylolites a petrographic and fluid inclusion microthermometric study was performed on sandstones containing abundant stylolites from the buchan galley and scott fields in the outer moray firth offshore scotland and from a palaeo oil bearing sequence in east greenland the main objective of this study was to further constrain the temperatures and burial depths at which stylolitization occurs in sandstone reservoirs the sandstones containing abundant stylolites are also characterized by their highly cemented nature numerous occurrences of quartz overgrowths clearly truncated by sutured stylolites are evident in all of the samples fluid inclusion microthermometry reveals that quartz cementation which is interpreted to be coeval with stylolitization occurred at minimum temperatures of between 86 and 136 c basin modelling of the scott and galley fields indicates that quartz cementation and stylolite development formed at depths greater than 2 5 km which were attained during rapid tertiary burial the occurrence of hydrocarbon fluid inclusions within healed microfractures orientated at high angles to the stylolites suggests that these microfractures provided pathways for hydrocarbon migration in the highly cemented low permeability zones associated with highly stylolitized sandstones

effects of a low level precursor and frontal stability on cyclogenesis during fastex iop17 the fronts and atlantic storm track experiment fastex has provided comprehensive data to document the life cycle of secondary frontal cyclones over the north atlantic and to improve the understanding of cyclogenesis mechanisms this study analyses the processes leading to the triggering of a particularly well sampled frontal cyclone that developed on the trailing cold front of a mature primary cyclone during fastex intensive observation period 17 iop17 between 16 and 20 february 1997 the case features both a classical low level vorticity strip along the primary front where the frontal cyclone develops and more unexpectedly a pre existing continental surface low further west the importance of which is revealed in the pilot study of arbogast and joly in order to study possible cyclogenetic contributions along the primary front the domain independent vorticity divergence attribution technique of bishop is used to partition the flow into contributions from the continental low and from the large scale environment results indicate that the frontal cyclone is triggered where and when along front stretching decreases below the theoretical critical threshold of bishop and thorpe it is shown that the cyclone is developing under normalized strain less than 1 in agreement with other case studies finally the role of the continental low is investigated using a series of numerical forecasts made from different initial conditions manipulated with a potential vorticity inversion tool the wind attributable to the continental low accounts for roughly 30 of the along front stretching decrease the continental low also has a frontolytic effect on the western part of the primary front where its thermal advection pattern favours cyclogenesis in general terms the frontal cyclone triggering seems to support the bishop and thorpe theoretical framework of frontal instability in low strain areas however a more complex picture arises when considering the role of the continental surface low which also acts as a low level precursor