the link between the north pacific climate variability and the north atlantic oscillation via downstream propagation of synoptic waves abstractthe north atlantic oscillation nao response to the northeast pacific climate variability is examined using the era 40 dataset the main objective is to validate a mechanism involving downstream wave propagation processes proposed in a recent idealized companion study a low frequency planetary scale ridge trough anomaly located in the eastern pacific north american sector induces more equatorward poleward propagation of synoptic scale wave packets on its downstream side which favors the occurrence of anticyclonic cyclonic wave breakings in the atlantic sector and the positive negative nao phase the mechanism first provides an interpretation of the canonical impact of the el nino southern oscillation on the nao in late winter the wintertime relationship between the pacific north american oscillation pna and the nao is also investigated for out of phase fluctuations between the pna and nao indices i e the most recurrent situation in late winter the eastern pacific pna ridge trou

understanding the contrasting north atlantic oscillation anomalies of the winters of 2010 and 2014 the present study investigates the two contrasting winters of 2010 and 2014 during which the north atlantic oscillation nao was mainly negative and positive respectively in the north pacific contrasting anomalies were also present with a straight zonal pacific jet in 2010 and a strong poleward deviation of the pacific jet in its exit region in 2014 using reanalysis data sets and adopting a nonlinear initial value approach with a quasi geostrophic model we show that the pacific north american anomalies are responsible for shaping synoptic wave trains propagating across north america this in turn largely determines the nature of wave breaking and the synoptic eddy feedback onto the mean flow in the north atlantic and finally the nao phase in such a proposed mechanism synoptic wave activity forms the cornerstone of the dynamical relationship between the north pacific and north atlantic large scale anomalies during the contrasting winters of 2010 and 2014

the role of synoptic waves in the formation and maintenance of the western hemisphere circulation pattern abstractprevious studies have demonstrated that the nao the leading mode of atmospheric low frequency variability over the north atlantic could be linked to northeast pacific climate variability via the downstream propagation of synoptic waves in those studies the nao and the northeast pacific climate variability are considered as two separate modes that explain the variance over the north atlantic sector and the east pacific north american sector respectively a newly identified low frequency atmospheric regime the western hemisphere wh circulation pattern provides a unique example of a mode of variability that accounts for variance over the whole north atlantic north american north pacific sector the role of synoptic waves in the formation and maintenance of the wh pattern is investigated using the ecmwf reanalysis datasets persistent wh events are characterized by the propagation of quasi stationary rossby waves across the north pacific north american north atlantic regions and by associated s

the structure of the rockall trough imaged by deep seismic reflection profiling westline is a 450 km long near normal incidence seismic reflection profile crossing the rockall trough from the rockall bank to the irish coast beneath rockall bank and the irish shelf unreflective upper crust overlies reflective lower crust and upper mantle crustal reflectors beneath the irish shelf are interpreted as caledonian the nw slope of the trough is dissected by a series of east dipping faults forming small sediment filled half grabens the steep se slope is formed by the erris ridge the floor of the trough is formed from rotated blocks separated by mainly east dipping faults wedges of sediment fill half grabens formed by this faulting there is no evidence for oceanic crust or a 9reflection moho9 within the trough the floor and slopes of the trough are blanketed by c 4 km of parallel bedded sediments the lower part of the parallel bedded sequence is intruded by sills and dykes that do not extend above a minor unconformity it is suggested that the bulk of the sediment preserved in the rockall trough accumulated during and following a major rifting event in the early or mid cretaceous

a new perspective toward cataloging northern hemisphere rossby wave breaking on the dynamic tropopause abstractrossby wave breaking rwb events are a common feature on the dynamic tropopause and act to modulate synoptic scale jet dynamics these events are characterized on the dynamic tropopause by

dynamical evolution of north atlantic ridges and poleward jet stream displacements the development of a particular wintertime atmospheric circulation regime over the north atlantic comprising a northward shift of the north atlantic eddy driven jet stream and an associated strong and persistent ridge in the subtropics is investigated several different methods of analysis are combined to describe the temporal evolution of the events and relate it to shifts in the phase of the north atlantic oscillation and east atlantic pattern first the authors identify a close relationship between northward shifts of the eddydriven jet the establishment and maintenance of strong and persistent ridges in the subtropics and the occurrence of upper tropospheric anticyclonic rossby wave breaking over iberia clear tropospheric precursors are evident prior to the development of the regime suggesting a preconditioning of the atlantic jet stream and an upstream influence via a large scale rossby wave train from the north pacific transient 2 6 days eddy forcing plays a dual role contributing to both the initiation and then the maintenance of the circulation anomalies during the regime there is enhanced occurrence of anticyclonic rossby wave breaking which may be described as low latitude blocking like events over the southeastern north atlantic a strong ridge is already established at the time of wave breaking onset suggesting that the role of wave breaking events is to amplify the circulation anomalies rather than to initiate them wave breaking also seems to enhance the persistence since it is unlikely that a persistent ridge event occurs without being also accompanied by wave breaking

crustal structure and magmatism of north atlantic continental margins enormous variations exist along rifted margins of the north atlantic in the magmatic activity that accompanied continental breakup the north atlantic margins exhibit a full range of magmatic behaviour one end of the spectrum commonly termed volcanic margins is found in the northern north atlantic off greenland norway and northwest britain where huge volumes of igneous rock were added to the continental crust as it rifted and the adjacent oceanic crust is considerably thicker than normal the other end of the spectrum so called non volcanic margins occurs further south off france and spain where only minor volcanism accompanied rifting and the oceanic crust immediately adjacent to the continental margin is thinner than normal oceanic crust results from seismic profiles are used to determine the volume and distribution of igneous crust accumulated as the continents broke up and seafloor spreading commenced the volume of melt produced during rifting is controlled mainly by the temperature of the underlying asthenospheric mantle and by the amount and rate of decompression as it rises beneath stretching and thinning lithosphere large quantities of igneous rock were produced as the continents broke up to form the north atlantic where the newly initiated iceland plume brought abnormally hot mantle beneath the rift much smaller quantities of melt were produced further south where mantle temperatures were normal during rifting the distribution of igneous rocks across the continental margin and the adjacent oceanic crust is controlled by the rate at which melt is produced and by the ease with which it can intrude laterally in the crust where the rate of stretching is very slow and the rifting is spread over many millions or even tens of millions of years as is common during the initial stages of rifting then the rising asthenospheric mantle has time to cool by conduction heat is lost from the asthenospheric mantle both vertically into the overlying water layer and laterally into the colder wedges of continental lithosphere on either side of the rifted region as a consequence of the reduced mantle temperatures considerably less partial melting occurs in the slowly rising asthenospheric mantle than in mantle which rises rapidly beneath rifts this explains the abnormally thin oceanic crust found adjacent to the non volcanic rifted continental margins in the north atlantic as the new ocean widens the spreading centre becomes isolated from the continental margins on either side by newly formed warm oceanic lithosphere and the rate of rifting generally increases the oceanic crust then attains its equilibrium thickness as conductive heat loss from the rising asthenospheric mantle reduces and all the melt formed by decompression of the mantle solidifies close to the spreading axis basaltic melts can intrude continental crust far more easily than oceanic crust basaltic dykes may extend many hundreds of kilometres away from the magma source beneath continental rifts this redistributes melt laterally towards the continent in both volcanic and to a lesser extent in non volcanic margins and may be a contributory factor in leaving unusually thin crust in the first formed ocean immediately adjacent to some rifted margins it also allows melt formed under volcanic rifts to migrate large distances laterally as is seen in the rockall area northwest of britain

neogene seismic facies and deep water gateways in the faeroe bank area ne atlantic abstract interpretation of sedimentary structures on high resolution multichannel sleeve gun seismic records has been used to illustrate changes in the neogene deep water flow regime around the bill bailey bank at the southern end of the faeroe shetland channel the main part of the norwegian sea overflow water nsow turns into the faeroe bank channel leaving the faeroe bank channel the nsow forms an erosive flow along the southern part of the faeroe platform where the basalt is outcropping it is indicated that part of the overflow waters continues to the northwest entering the n atlantic basin to the west of the faeroe rockall plateau intermittent overflow of nsow occurs via the wyville thomson ridge complex between the bill bailey bank and faeroe bank sedimentary structures seen on the seismic profiles indicate the existence of a former nsow pathway which was active until presumably the late pliocene along the southern rise of the bill bailey bank the seismic profiles indicate that deep water flow was still active in the late quaternary which presumably can be related to intermittent overflow of the wyville thomson ridge complex

seismic evidence for early tertlary bottom current controlled deposition in the charlie gibbs fracture zone abstract buried mounded and acoustically transparent sediment bodies banked up against a basement ridge at the eastern end of the charlie gibbs fracture zone are interpreted as a type of contourite drift as they are probably of eocene palaeocene age their origin has implications for the little known deep circulation pattern in the ne atlantic during this period possible sources for the bottom currents responsible for these drifts include labrador sea water norwegian sea overflow water antarctic bottom water or a gulf stream deep gyre system the preferred source is an early development of antarctic bottom water or an arm of a gulf stream gyre flowing eastwards through the fracture zone

tropospheric rossby wave breaking and the nao nam objective analysis of several hundred thousand anticyclonic and cyclonic breaking rossby waves is performed for the northern hemisphere nh winters of 1958 2006 a winter climatology of both anticyclonic and cyclonic rossby wave breaking rwb frequency and size zonal extent is presented for the 350 k isentropic surface over the nh and the spatial distribution of rwb is shown to agree with theoretical ideas of rwb in shear flow composites of the two types of rwb reveal their characteristic sea level pressure anomalies upper and lower tropospheric velocity fields and forcing of the upper tropospheric zonal flow it is shown how these signatures project onto the centers of action and force the velocity patterns associated with the north atlantic oscillation nao and northern hemisphere annular mode nam previous studies have presented evidence that anticyclonic cyclonic breaking leads to the positive negative polarity of the nao and this relationship is confirmed for rwb over the midlatitudes centered near 50 n however an opposite and statistically significant relationship in which cyclonic rwb forces the positive nao and anticyclonic rwb forces the negative nao is shown over regions 20 to the north and south centered at 70 and 30 n respectively on a winter mean basis the frequency of rwb over objectively defined regions covering 12 of the area of the nh accounts for 95 of the nao index and 92 of the nam index a 6 hourly analysis of all the winters indicates that rwb over the objectively defined regions affects the nao nam without a time lag details of the objective wave breaking analysis method are provided in the appendix

quaternary glaciations of northern europe this paper presents the outcome of a workshop held in berlin in february 2009 concerned with current research on the glacial history of northern europe including the british isles the methodologies presently used to resolve this topic are outlined particular attention is given to new analytical methods deriving from high resolution remote imaging of glacial terrain both on land and on the sea bed key new stratigraphic sections higher resolution results from conventional geochronological methods like radiocarbon and more recently developed technologies such as luminescence and cosmogenic radionuclide dating the relationships between the results derived from these two methods are discussed in further detail along with possible explanations for these differences an outline of a most likely glacial history of the scandinavian and british and irish ice sheets is presented along with possible links to global climate change as represented by the marine isotope mis record tentative evidence for glaciation is identified in mis 22 16 12 10 8 6 4 and 2 and correlations of phases within the last glaciation are also explored for both the scandinavian and british and irish ice sheets the results show that the character and extent of glaciation in different parts of the region are not synchronous and much more geochronological work is required before regional correlations can be established with confidence

cenozoic alongslope processes and sedimentation on the nw european atlantic margin based on studies of sediment accumulations deposited from and erode by alongslope flowing ocean currents on the european continental margin from porcupine ireland to lofoten norway the evolution of the cenozoic paleocirculation was reconstructed as part of the stratagem project there is evidence of ocean current controlled erosion and deposition in the rockall trough in the faeroe shetland channel and on the voring plateau since the late eocene although the circulation pattern remains ambiguous the late palaeogene flow in the rockall trough was almost probably driven by southerly derived tethyan outflow water the extent and strength of any northerly derived flow is uncertain from the early neogene early mid miocene there was a massive regional expansion of contourite drift development both in the north atlantic and in the norwegian greenland sea this was most probably related to the development of the faroe conduit the opening of the fram strait and the general subsidence of the greenland scotland ridge these may have combined to cause a considerable acceleration in the exchange and overflow of deep waters between the arctic and atlantic oceans an early late neogene late early pliocene regional erosional event has been ascribed to a vigorous pulse of bottom current activity most probably the result of a global reorganisation of ocean currents associated with the closure of the central american seaway during the late neogene contourites and sediment drifts developed in deep water basins between units of glacigenic sediments as well as infill of several paleo slide scars these sediments were derived from areas of bottom current erosion as well as from the development of plio pleistocene prograding sediment wedges incorporating the extensive sediment supply derived from shelf wide ice sheets presently a profound winnowing prevails along the shelf and upper slope due to the inflowing currents of atlantic water depocentres of sediments derived from the winnowing are located locally in lower slope embayments and in slide scars

plate reorganization a cause of rapid late neogene subsidence and sedimentation around the north atlantic subsidence analysis of wells in the central north sea and labrador grand banks and oft the west greenland scotian shelf and united states atlantic margin shows distinct quantitative stratigraphic correlation patterns of circum north atlantic sites a significant departure from the overall decrease in subsidence for the pliocene occurs in many wells when the rate is found to have increased one or more orders of magnitude from oligocence miocene rates wells were selected along transects from shore to basin to find if relative basin position is influenced by differential basin subsidence although stratigraphic resolution is not detailed more basinward sites experienced up to four times larger subsidence rates in the late neogene than in the oligocene miocene with a peak in the pliocene wells at the basin edge experienced much less subsidence or showed uplift the observations are consistent with a rapid change of intraplate stress at the cause for this observed transition in neogene subsidence major reorganizations of spreading direction and rate occurred during the pliocene along the entire atlantic spreading system possibly in conjunction with more global changes in plate motions we propose that the associated changes in intraplate stress caused the excess margin subsidence relative uplift along basin edges is consistent with this mechanism of relative movement and may explain apparent eustatic changes in sea level

a record of late cenozoic stratigraphy sedimentation and climate change from the hebrides slope ne atlantic ocean a punctuated 103 3 m thick succession of upper palaeogene to quaternary sediments has been recovered in a borehole from the upper hebrides slope west of britain the borehole proved 11 2m of upper oligocene carbonate rich muds at the base unconformably overlain by 2 85 m of middle to upper miocene glauconitic sands this is in turn unconformably overlain by 89 25 m of predominantly plio pleistocene sands and muds with a holocene sea bed veneer the post miocene succession is subdivided into two units the sand dominated pliocene to lower middle pleistocene lower macleod sequence between 89 25 and 67 82 m and the mud dominated middle pleistocene to holocene upper macleod sequence above 67 82 m regional mapping indicates that these sequences are commonly associated with large scale shelf margin progradation and slope front fan construction the borehole core provides an excellent record of the transition from pre glacial to glacial conditions in the mid latitude ne atlantic ocean climatic conditions warmer than present prevailed in the late oligocene mid to late miocene and pliocene although the influx of ice rafted detritus in the late pliocene marks the onset of climatic deterioration this deterioration continued in a fluctuating manner until the early mid pleistocene 0 44 ma when fully glacial conditions were established on the hebridean margin

on double rossby wave breaking in the north atlantic we discuss the dynamical features associated with double rossby wave breaking dwb concurrent cyclonic and anticyclonic breakings over the north atlantic with a focus on the north atlantic oscil

the north atlantic oscillation response to large scale atmospheric anomalies in the northeastern pacific abstractingredients in the north pacific flow influencing rossby wave breakings in the north atlantic and the intraseasonal variations of the north atlantic oscillation nao are investigated using both reanalysis data and a three level quasigeostrophic model on the sphere first a long term run is shown to reproduce the observed relationship between the nature of the synoptic wave breaking and the phase of the nao furthermore a large scale low frequency ridge anomaly is identified in the northeastern pacific in the days prior to the maximum of the positive nao phase both in the reanalysis and in the model a large scale northeastern pacific trough anomaly is observed during the negative nao phase but does not systematically precede it then short term linear and nonlinear simulations are performed to understand how the large scale ridge anomaly can act as a precursor of the positive nao phase the numerical setup allows for analysis of the propagation of synoptic waves in the eastern pacific in the p

reconstructing sea level pressure variability via a feature tracking approach abstractthe aim of this paper is to quantify the contribution of synoptic transients to the full spectrum of space time variability of sea level pressure slp in middle latitudes in previous work by the authors it was shown that tracking cyclones and anticyclones in an idealized atmospheric model allows one to reconstruct a surprisingly large fraction of the model s variability including not only synoptic components but also its large scale low frequency component motivated by this result the authors performed tracking of cyclones and anticyclones and estimated cyclone and anticyclone size and geometry characteristics in the observed slp field using the 1948 2008 ncep ncar reanalysis dataset the reconstructed synoptic field was then produced via superimposing radially symmetrized eddies moving along their actual observed trajectories it was found that similar to earlier results for an idealized model the synoptic reconstruction so obtained accounts for a major fraction of the full observed slp v

late cenozoic sediment drift complex northeast rockall trough north atlantic seismic reflection profiles and two shallow cores have revealed a sediment drift complex in the northeastern rockall trough the drift complex consists of an elongate drift with associated sediment waves a broad sheeted drift with a larger field of sediment waves and smaller moat related isolated drifts the internal reflection configuration of these features indicates consistent upslope migration throughout the late cenozoic the larger field of sediment waves has been described previously with a southerly migration a reevalution of these waves suggests a migration direction to the east conforming with the other drift complex features the most vigorous current activity probably occurred during the miocene with a more reduced current flow prevailing during the pliocene to holocene interval core evidence from the elongate drift and the moat has revealed upper pleistocene and lower holocene glaciomarine sediments reworked to produce muddy silty and sandy contourites sedimentation rates for the early holocene pre 7 5 ka are up to 4 times greater on the drift compared to the moat it is suggested that the sediment drift complex has formed through the interaction of a northward flowing slope current of north atlantic deep water origin with an area of complex bathymetry at the northeastern end of the rockall trough where the wyville thomson ridge intersects the hebridean margin

contributions of downstream eddy development to the teleconnection between enso and the atmospheric circulation over the north atlantic abstractthe spatiotemporal evolution of various meteorological phenomena associated with el nino southern oscillation enso in the north pacific north american north atlantic sector is examined using both ncep ncar reanalyses and output from a 2000 yr integration of a global coupled climate model particular attention is devoted to the implications of downstream eddy developments on the relationship between enso and the atmospheric circulation over the north atlantic the el nino related persistent events are characterized by a strengthened pacific subtropical jet stream and an equatorward shifted storm track over the north pacific the wave packets that populate the storm tracks travel eastward through downstream development the barotropic forcing of the embedded synoptic scale eddies is conducive to the formation of a flow that resembles the negative phase of the north atlantic oscillation nao the more frequent and higher persistence of those episodes during el nino winters contribute to the prevale

how rossby wave breaking over the pacific forces the north atlantic oscillation 1 anticyclonic rossby wave breaking rwb over a well defined limited area region of the east pacific leads to the positive polarity of the north atlantic oscillation nao by locally piling up wave activity where it may be advected downstream resulting in increased wave activity flux and anticyclonic rwb over the subtropical atlantic a composite time series shows that pacific rwb occurs several days prior to the atlantic rwb and the peak of the nao index following pacific rwb a channel of increased pseudomomentum flux extends from the pacific wave breaking region northeastward toward midlatitudes of eastern north america where pseudomomentum density accumulates for several days prior to moving eastward and leading to anticyclonic rwb over the atlantic

the velocity structure of the sediments in the southern rockall basin results from new wide angle seismic modelling abstract travel time modelling of first and second arrivals have been used to produce p wave velocity models of the sedimentary structure on three new wide angle reflection refraction profiles from the irish sector of the rockall basin the models indicate a sedimentary succession that is typically 4 5 km thick and reaches a maximum thickness of 7 km the sediments are typically horizontal within the basin centre but display significant structural complexities towards the margins where sediment depocentres and large fault blocks are interpreted up to seven layers with velocities ranging from 1 8 to 5 2 km s 1 have been resolved within which three distinct seismic packages have been identified an upper package interpreted as oligocene and neogene in age is approximately 1 5 km thick and confined within the rockall basin pinching out onto the basin margins this overlies a structurally complex middle package ca 1 5 km thick confined predominantly within the basinal areas which is interpreted as being of cretaceous to early tertiary age a regionally extensive lower package up to 4 km thick is interpreted as being of probable late palaeozoic to jurassic age the new data provide a much clearer picture than was hitherto available of the entire sedimentary succession in the basins that underlie the rockall trough they show a significant variability in thickness of the various sedimentary layers and in particular illustrate a marked topographic irregularity at the base of the sedimentary succession

cenozoic sediment accumulation on drifts in the northern north atlantic the northern north atlantic sediment drifts have a much greater areal extent than has previously been indicated the northern north atlantic extends from the east greenland to european continental shelves and from the charlie gibbs fracture zone to the greenland scotland ridge within this region are seven major sediment drifts containing some of the best clues for pre quaternary bottom water circulation in the north atlantic feni drift is the oldest in the region originating near the eocene oligocene boundary it was followed by accumulation of bjorn gardar hatton and snorri drifts from the late early to middle miocene eirik drift may have started to accumulate in the late miocene and gloria drift in the early pliocene through analysis of the cenozoic sediment mass age distribution and the change in area of seafloor for the study area through time it can be concluded that there is a deficit of oligocene to miocene sediment in the region this could be explained by sediment cycling the erosion of older sediment to produce young sediment the mass of pliocene to quaternary sediment is much larger than that of the older sediment and may have been derived primarily through the erosion of eocene and oligocene sediment by deepwater currents the sediment drift portion of the total regional sediment mass increased significantly three times during the cenozoic each of these drift growth phases lasted between 3 and 4 m y the first two growth phases from the late eocene to early oligocene and from the early to middle miocene were accompanied by northward shifts of depocenters to the newly forming sediment drifts the third and largest growth phase occurred between 7 and 3 ma and may have been preceded by the initiation of accumulation on eirik drift 8 7 ma this most recent growth phase was accompanied by high apparent accumulation rates over southern gardar drift as it expanded to the east erosion rates over reykjanes ridge may have been higher during the mid pliocene than in the quaternary there are two main sites where dense water could have formed and flowed south through the rockall trough to start the accumulation of feni drift if the atmosphere were cool enough dense water could have formed in the norwegian sea or on the faeroe shelf dense water may also have formed on the rockall plateau due to salinity increase through evaporation in an arid climate as an alternative to the hypothesis of arctic ocean water overflowing the iceland faeroe ridge in the early middle miocene it is suggested that dense water formed along shallow segments of the iceland faeroe ridge and then flowed into the south iceland basin to begin accumulation of bjorn gardar and snorri drifts the initiation of sediment drift formation in the south iceland basin may have been caused by a decreased rate of deep water production combined with a higher rate of detrital input due to a middle miocene uplift event along the iceland faeroe ridge a second uplift event along the greenland scotland ridge and a decreased production of northern component water in the early pliocene may be responsible for increased sediment accumulation in bjorn gardar and eirik drifts

anatomy of synoptic eddy nao interaction through eddy structure decomposition abstracta method of eddy structure decomposition is proposed to detect how low frequency flow associated with the north atlantic oscillation nao organizes systematically synoptic eddy se activity to generate in phase and upstream feedbacks in this method a statistical eddy streamfunction ses field defined by the three point covariance of synoptic scale streamfunction is introduced to characterize spatiotemporal se flow structures the ses field is decomposed into basic and anomalous parts to represent the climatological se flow structure and its departure these two parts are used to calculate the basic and anomalous eddy velocity eddy vorticity and thus eddy vorticity flux fields in order to elucidate those two se feedbacks onto the nao this method is validated by the fact that the observed anomalous eddy vorticity flux field can be reproduced well by two linear terms the basic eddy velocity field multiplied by anomalous eddy vorticity field and the anomalous eddy velocity field multiplied

the shift of the northern node of the nao and cyclonic rossby wave breaking abstractseveral studies have found an eastward shift in the northern node of the north atlantic oscillation nao during the winters of 1978 97 compared to 1958 77 this study focuses on the connection between this shift of the northern node of the nao and rossby wave breaking rwb for the period 1958 97 it is found that the region of frequent cyclonic rwb underwent a northeastward shift at high latitudes in the latter 20 yr period on a year to year basis the cyclonic rwb region moves along a southwest northeast sw ne directed axis both latitude and longitude of the winter maximum frequency of cyclonic rwb occurrence are positively correlated with the nao index to investigate the role of location of cyclonic rwb in influencing the nao pattern the geographical location of frequent cyclonic rwb is divided into two subdomains located along the sw ne axis to the south sw domain and east ne domain of greenland two composites are assembled as one cyclonic rwb occurrence is detected in one of the t

synoptic view of the north atlantic oscillation abstract this article investigates the synoptic characteristics of individual north atlantic oscillation nao events by examining the daily evolution of the potential temperature field on the nominal tropopause the 2 pvu surface this quantity is obtained from the national centers for environmental prediction national center for atmospheric research ncep ncar reanalysis dataset for the winter season for both phases the nao is found to originate from synoptic scale waves as these waves evolve into the low frequency nao pattern they break anticyclonically for the positive phase and cyclonically for the negative phase the results of this analysis suggest that it is the remnants of these breaking waves that form the physical entity of the nao throughout the nao events for both phases the nao is maintained by the successive breaking of upstream synoptic scale waves when synoptic scale disturbances are no longer present mixing processes play an important role in the nao decay as in other recent

sediment drifts and contourites on the continental margin off northwest britain abstract seismic reflection profiles and short cores from the continental margin off northwest britain have revealed a variety of sediment drift styles and contourite deposits preserved in the northeast rockall trough and faeroe shetland channel the sediment drifts include 1 distinctly mounded elongate drifts both single and multi crested 2 broad sheeted drift forms varying from gently domed to flat lying and 3 isolated patch drifts including moat related drifts fields of sediment waves are locally developed in association with the elongate and gently domed broad sheeted drifts the contrasting styles of the sediment drifts most probably reflect the interaction between a variable bottom current regime and the complex bathymetry of the continental margin the bulk of the mounded gently domed drifts occur in the northeast rockall trough whereas the flat lying sheet form deposits occur in the faeroe shetland channel a much narrower basin which appears to have been an area more of sediment export than drift accumulation patch drifts are present in both basins in the northeast rockall trough the along strike variation from single to multi crested elongate drifts may be a response to bottom current changes influenced by developing drift topography muddy silty muddy and sandy contourites have been recovered in sediment cores from the uppermost parts of the drift sequences on the basis of their glaciomarine origin these mid to high latitude contourites can be referred to collectively as glacigenic contourites both partial and complete contourite sequences are preserved the former consist largely of sandy mid only and top only contourites sandy contourites by their coarse grained nature and their formation under strongest bottom current flows are the most likely to be preserved in the rock record however the very large scale of sediment drifts should be borne in mind with regard to the recognition of fossil contourites in ancient successions

seismic stratigraphy of the west shetland drift implications for late neogene paleocirculation in the faeroe shetland gateway 1 the morphology and anatomy of a late neogene contourite drift on the british margin of the faeroe shetland channel is investigated in unprecedented detail using industrial two dimensional and three dimensional seismic data the west shetland drift is constructed by a succession of mounded asymmetric strata that in the basin and on the midslope has accumulated on a regional unconformity of early pliocene age the midslope component of the drift system forms a 400 m thick convex elongate sedimentary body that can be traced from the outlet of the norwegian channel and 250 km southwest along the shetland margin contourite drifts occupying the basin are evident as a succession of sheeted mounded and wavy migrating units intercalated by three mega debrite sequences the seismic architecture of the west shetland drift and tentative age estimates of its bounding surfaces suggests that it formed rapidly 5 10 cm kyr 1 by alongslope transport of hemipelagic sediments derived from the nw european shelf the change from erosion nondeposition to enhanced contourite drift accumulation during the early pliocene suggests that a moderate thermohaline current regime prevailed in the faeroe shetland channel prior to the main phase of northern hemisphere glaciation at 3 0 2 5 ma a reduction in meridional heat transport associated with a decrease in the flux of north atlantic deep waters may have been an important factor for the growth of northern hemisphere ice sheets

tropical and subtropical north atlantic vertical wind shear and seasonal tropical cyclone activity abstractgiven recent insights into the role of anticyclonic rossby wave breaking awb in driving subseasonal and seasonal north atlantic tropical cyclone tc activity this study further examines

impact of midlatitude stationary waves on regional hadley cells and enso 1 stationary planetary waves are excited in the midlatitudes propagate equatorward and are absorbed in the subtropics the impact these waves have on the tropical climate has yet to be fully unraveled previous work has shown that interannual variability of zonal mean stationary eddy stress is well correlated with interannual variability in hadley cell strength a separate line of research has shown that changes in midlatitude planetary waves local to the pacific strongly affect enso variability here we show that the two phenomena are in fact closely connected interannual variability of wave activity flux impinging on the subtropical central pacific affects the local hadley cell the associated changes in subtropical subsidence affect the surface pressure field and wind stresses which in turn affect enso as a result a winter with an anomalously weak hadley cell tends to be followed a year later by an el nino event

the role of dynamic tropopause rossby wave breaking for synoptic scale buildups in northern hemisphere zonal available potential energy abstractzonal available potential energy az measures the magnitude of meridional temperature gradients and static stability of a domain here the role of northern hemisphere dynamic tropopause 2

the southern margin of the rockall plateau stratigraphy tertiary volcanism and plate tectonic evolution the geological evolution of the southwest rockall plateau in the area of edoras bank has been clarified using seismic reflection gravity and magnetic data four principal reflectors are observed within the tertiary sedimentary sequence i late miocene ii latest early miocene iii late eocene iv earliest eocene a period of pronounced sediment drift accumulation marks the interval i ii reflector iii the top of a sediment wedge prograding southward from edoras bank marks a change from terrigenous to pelagic sedimentation that is probably related to subsidence of the rockall plateau following the separation of greenland from eurasia in the earliest eocene reflector iv marks the top of a wedge shaped seismically transparent layer that also thins southward away from edoras bank on the basis of its seismic attributes and magnetic signature this layer is interpreted as a volcanic sheet formed as part of the north atlantic tertiary volcanic province during rifting of greenland from eurasia the recognition of voluminous volcanic rocks south of edoras bank extends the known area of the tertiary volcanic province several hundred kilometres to the south gravity anomaly modelling and continental reconstructions suggest that the region south of edoras bank is underlain by thinned continental crust a four stage geological evolution for this region is indicated i initial rifting associated with the separation of labrador from greenland in the late cretaceous is characterized by enhanced crustal thinning and subsidence in the region of a rift triple junction ii passive subsidence and accumulation of late cretaceous and earliest tertiary sediments followed the initiation of seafloor spreading in the labrador sea iii blanketing of the area by palaeocene volcanic rocks masked pre existing magnetic lineations providing an explanation for some of the problems in earlier interpretations based mainly on magnetic data iv post volcanic sedimentation continuing to the present day

linking atmospheric river hydrological impacts on the u s west coast to rossby wave breaking abstractatmospheric rivers ars have significant hydrometeorological impacts on the u s west coast this study presents the connection between the characteristics of large scale rossby wave breaking rwb over the eastern north pacific and the regional scale hydrological impacts associated with landfalling ars on the u s west coast 36 49 n ars associated with rwb account for two thirds of the landfalling ar events and 70 of total ar precipitation in the winter season the two regimes of rwb anticyclonic wave breaking awb and cyclonic wave breaking cwb are associated with different directions of the vertically integrated water vapor transport ivt awb ars impinge in a more westerly direction on the coast whereas cwb ars impinge in a more southwesterly direction most of the landfalling ars along the northwestern coast of the united states states of washington and oregon are awb ars because of their westerly impinging angles when compared to cwb ars awb ars arrive more orthogonally to the

sequence stratigraphic analysis in deep water underfilled nw european passive margin basins sequence stratigraphic analysis is now carried out routinely on mesozoic cenozoic sedimentary basins with a view to understanding their post rift stratal geometries and predicting facies architecture the conventional method embodies two concepts the physical division of strata into unconformity bounded units and their genetic interpretation on the assumption that hierarchical changes in sea level represent the primary control on sedimentary architecture the genetic model is reflected in a complex descriptive terminology and derives from the development of the method in shallow water basins where the results of analyses typically accord with geological data constraints applied to deep water underfilled basins however the sea level assumption yields results that are unsatisfactory and in many cases misleading reflecting the influence of additional controls including tectonic movements deep sea currents and climate e g glaciation on stratal geometries and facies architecture this is illustrated by comparative analyses of examples from the deep water cenozoic basins of the nw european atlantic passive margin which contain a set of seismic megasequences bounded by unconformable to conformable surfaces correlative from shelf to slope to basinal settings the deep water successions contain regional locally diachronous submarine unconformities that were generated in response to changes in deep water current circulation and slope processes rather than subaerial erosion these bound aggradational contourite drifts that include upslope accretion against basin margins the deep water successions interfinger at two levels with seaward prograding shelf slope wedges that reflect differential tectonic movements involving coeval uplift and subsidence the youngest wedges formed in the last 4 ma and record seaward progradation of the margin by up to 100 km overprinting high amplitude variations in sea level and coeval with changes in deep ocean currents sediment supply by fluvial sources gave way in the pleistocene to direct glacial sediment supply to the slope in all these instances the stratal geometries and facies architecture cannot be attributed to a simple lowering of regional sea level but instead reflect a complex interplay of controlling factors including tectonic movements changes in sediment supply deep water current activity and climate in addition to sea level sequence stratigraphic analysis in such settings must recognise and evaluate alongslope downslope and vertical components of sediment supply

rounded mineral inclusions in upper mantle peridotite abstract mantle derived peridotite xenoliths contain abundant olivine with rounded spinel and orthopyroxene inclusions and orthopyroxene with rounded olivine and spinel inclusions the shape change of spinel olivine and orthopyroxene inclusions from the primarily polyhedral outline to the spherical outline is governed by interfacial diffusion of oxygen in spinel the most sluggish atom due to reduction of total interfacial energy of the host inclusion system the critical radius of maximum rounded inclusions of spinel in olivine is a function of temperature and annealing time assuming that the activation energy for the interfacial diffusion is 40 70 kcal mol 1 and that the annealing time for the spinel lherzolite from salt lake crater in hawaii is 100 ma the annealing times for perioditites under the island arcs of japan are estimated to be 1 10 ma

mid to late cenozoic sedimentation on the continental margin off nw britain the present morphological expression of the continental margin off nw britain is a mid to late cenozoic phenomenon initiated by a major phase of rapid subsidence in the rockall trough and hatton rockall basin during the early late eocene this led to a deepening of the basins and the onset of bottom current activity in this region on seismic reflection profiles this basin subsidence event is manifest in the form of a widespread deep water unconformity caused by bottom current erosion this boundary is particularly enhanced at the basin margins and adjacent to the axial seamounts of rosemary bank and anton dohrn where the downwarped and eroded surface of lower upper eocene and older strata is onlapped by middle to upper cenozoic sediments the latter comprise two megasequences of late eocene to mid miocene and mid miocene to holocene age which consist predominantly of deep marine contourites both in the rockall trough and the hatton rockall basin although a clastic wedge has built out along the hebridean shelf margin since the mid miocene these megasequences reflect a gross two stage depositional history a response to intra plate tectonism which modified sedimentation patterns and palaeoceanographic circulation the development of the bounding unconformities early late eocene and mid miocene was coincident with major phases of regional tectonism

characteristics of the atlantic storm track eddy activity and its relation with the north atlantic oscillation abstract this study focuses on feedbacks of the high frequency eddy activity onto the quasi stationary circulation particularly with regard to the north atlantic oscillation nao the methodology consists of analyzing ncep ncar reanalysis data and sensitivity runs from a high resolution nonhydrostatic regional model consistent with recent studies results show that the jet displacement characteristic of the nao phenomenon depends strongly on the dynamics of the synoptic scale waves and the way they break positive and negative phases of the nao are closely related to anticyclonic and cyclonic wave breaking respectively indeed the high frequency momentum flux whose sign is directly related to the type of wave breaking is correlated with the nao index over the atlantic the peak of the momentum flux signal precedes that of the nao by a few days suggesting that wave breaking is triggering nao events two examples illustrate the significant impact of single storms in particular those occurring in the e