propagation of the great salinity anomaly of the 1990s around the northern north atlantic 1 time series of t and s extending through 2001 are used to describe propagation of the great salinity anomaly of the 1990s gsa 90s comparison of the distance time relations for the gsa 70s 80s and 90s reveals a substantial intensification of the large scale circulation in the northern north atlantic especially in the subarctic gyre between newfoundland and the faroes the advection rate of the gsa 70s 80s and 90s between newfoundland and the faroe shetland channel is conservatively estimated to have been 3 5 10 and 10 cm s respectively the circulation intensification apparently occurred within a decade between the gsa 70s and 80s during the next decade the advection rate increased from 10 to 13 cm s between newfoundland and iceland basin the gsa 90s was advected towards the faroe shetland channel by the northern iceland basin s branch of the north atlantic current whereas the contribution of the southern branch via the rockall trough was minimal

major pathways of atlantic water in the northern north atlantic and nordic seas toward arctic 1 the major pathways of near surface atlantic water in the northern north atlantic and nordic seas are identified as current speeds above 30 cm s using 1014 lagrangian drifters combined with previously published hydrography the inflow over the scotland greenland ridge and establishment of the two branch norwegian atlantic current nwac are described in light of the circulation in the northern north atlantic the western branch of the nwac appears as a jet in the polar front topographically guided from the iceland faroe front through the nordic seas toward fram strait the eastern branch starts as a shelf edge current above the irish scottish continental shelf and after passing through the faroe shetland channel it continues northward along the norwegian shelf edge toward the arctic with a branch bifurcating into the barents sea the nwac appears to maintain its two branch structure throughout the nordic seas with the atlantic water confined to a 200 600 km wide wedge

fabric transitions from shell accumulations to reefs an introduction with palaeozoic examples one unresolved conceptual problem in some palaeozoic sedimentary strata is the boundary between the concepts of shell concentration and reef in fact numerous bioclastic strata are transitional coquina reef deposits because either distinct frame building skeletons are not commonly preserved in growth position or skeletal remains are episodically encrusted by stabilizer reef like organisms such as calcareous and problematic algae encrusting microbes bryozoans foraminifers and sponges the term parabiostrome coined by kershaw can be used to describe some stratiform bioclastic deposits formed through the growth and destruction by fair weather wave and storm wave action of meadows and carpets bearing frame building archaeocyaths bryozoans corals stromatoporoids etc and or epibenthic non frame building e g pelmatozoan echinoderms spiculate sponges and many brachiopods organisms this paper documents six palaeozoic examples of stabilized coquinas leading to pseudo reef frameworks some of them formed by storm processes generating reef soles aborted reefs or being part of mounds on ramps and shelves and were consolidated by either encrusting organisms or early diagenesic processes whereas others bioclastic dominated shoals in barrier shelves were episodically stabilized by encrusting organisms indicating distinct episodes in which shoals ceased their lateral migration a paramount quantity of information characterizes the formation and distribution of shell concentrations and reefs in modern and cenozoic strata but the knowledge of phanerozoic shell concentrations and reefs is decreasing when increasing in age the palaeozoic is a key time span in the history of life owing to the wide occurrence of skeletonized metazoans the so called cambrian explosion zhuravlev riding 2000 and the successive biodiversifications related to i major extinctions such as the end ordovician cooper 2004 the frasnian famenian boundary buggisch 1991 copper 2002 racki house 2002 and the endpermian extinction wignall hallam 1992 and ii major community replacements such as the lower middle cambrian transition 2 j j alvaro et al remains webb 1996 following wood s 1998 definition reefs develop due to the aggregation of sessile epibenthic marine organisms with the resultant higher rate of in situ carbonate production than in surrounding sites although the relative capacity of some gregarious epibenthic organisms bearing mineralized skeletons to be preserved in living position is a common characteristic of reef organisms this character is also shared with other non reef metazoans adapted to soft substrates and forming bundles like clusters one group of these organisms named secondary soft bottom dwellers by seilacher 1984 differs from mud stickers e g non encrusting pelmatozoans and sponges in the heavy weight of their shells these metazoans mainly brachiopods and molluscs develop common cup boulderand fan shaped convergent morphologies favouring recliner strategies seilacher 1984 savazzi 1999 skeletal concentrations can be subdivided according to their biostratinomic features into biogenic sedimentary diagenetic and mixed concentrations kidwell et al 1986 biogenic concentrations can be intrinsic or extrinsic in character the former generated by the organisms that produce the hard parts resulting from intrinsic gregarious behaviours of autochthonous and parautochthonous skeletal organisms e g preferential colonization by larvae and single colonization events of opportunistic species and the latter produced by other organisms that interact with skeletonized organisms on their discarded hard parts leading to the formation of parautochthonous and allochthonous concentrations e g hard part rich fecal masses and shell filled pits sedimentary concentrations result from physical usually hydraulic processes of concentration in which hard parts behave as sediment particles and non bioclastic matrix is either reworked or fails to accumulate e g shelly storm lags aeolian beach pavements channel lags in fluvial intertidal and subtidal environments or shell paved turbidities diagenetic concentrations form or are significantly enhanced by processes acting after burial such as compaction or selective dissolution of matrix and finally mixed concentrations form by the interplay of two or more kinds of the aforementioned processes and can display both autochthonous parautochthonous and allochthonous shell

seasonal cycle of mesoscale instability of the west spitsbergen current abstractthe west spitsbergen current wsc is a topographically steered boundary current that transports warm atlantic water northward in fram strait the 16 yr 1997 2012 current and temperature salinity measurements from moorings in the wsc at 78 50 n reveal the dynamics of mesoscale variability in the wsc and the central fram strait a strong seasonality of the fluctuations and the proposed driving mechanisms is described in winter water is advected in the wsc that has been subjected to strong atmospheric cooling in the nordic seas and as a result the stratification in the top 250 m is weak the current is also stronger than in summer and has a greater vertical shear this results in an e folding growth period for baroclinic instabilities of about half a day in winter indicating that the current has the ability to rapidly grow unstable and form eddies in summer the wsc is significantly less unstable with an e folding growth period of 2 days observations of the eddy kinetic energy eke show a p

wind and buoyancy induced transport of the norwegian coastal current in the barents sea 1 the focus of this study is on the fluxes and forcing of the norwegian coastal current ncc at the entrance to the barents sea the structure and dynamics of the ncc which consists of a slope branch and an offshore branch are investigated using 1 a recent 1 year full depth current meter record in the core of the slope region 2 repeated hydrographic data at an inshore monitoring station 3 broader regional hydrographic surveys and 4 atmospheric reanalysis data the total fluxes are estimated to 1 8 sv for volume and 26 msv for freshwater relative to a reference salinity of 34 8 with the largest contributions from baroclinic offshore branch the heat flux calculated for the slope branch only is 34 tw these estimates are higher compared to earlier estimates but are based on more comprehensive data the major mode of variability in the slope branch is consistent with a continental shelf wave on time scales in the range of 3 16 days forced by the along coast component of the wind stress maximum along slope currents during fall winter corresponding to the stronger wind forcing during these seasons suggest that the observed seasonality in the ncc can be attributed to a similar mechanism

early palaeozoic cooling events peri gondwana and beyond the short lived end ordovician hirnantian glaciation allied to marine mass extinction is variously considered as a short lived event or as the peak of long drawn out climatic cooling through at least late ordovician early silurian times evidence from early palaeozoic facies faunas and stable isotope excursions used to interpret climatic cooling events ranges farther from late mid cambrian to late silurian times glacigenic sediments structures and geomorphology provide direct evidence of glacial episodes cool water carbonate deposition which is particularly widespread during the late ordovician boda event in high latitude peri gondwana gondwana and beyond into mid low palaeolatitudes is interpreted as indicating global cooling not warming as has been proposed such carbonates also characterize mid latitude continents widely at horizons earlier in the ordovician and more locally in the mid silurian in high latitude gondwana cool water carbonate mounds have distinctive facies controlled mound faunas across palaeocontinents other facies evidence for palaeoclimates includes black shale deposition including deglacial organic rich hot shales which indicate transgression in epeiric seas and sea level curves interpreted from facies and faunal successions correlation is shown between facies evidence and positive c isotope excursions from which cyclicities are apparent the possible interface of orbitally controlled rhythms is considered against evolving palaeobiogeography and changes in global sea level and in pco2 facies and faunal evidence from peri gondwanan terranes armorica central europe alborz is assessed with that from gondwana mostly north africa south america and correlatives in avalonia baltica and laurentia to establish a wider picture of early palaeozoic cooling events

late ordovician global warming the boda event there is substantial evidence for mid ashgillian global warming before the latest ordovician hirnantian glaciation as shown by the movement of previously lower latitude benthic faunas such as trilobites and brachiopods to progressively higher latitudes and by an increase in endemic faunas at low latitudes this is shown by faunal dynamics on several paleocontinents and endorsed by published evidence of warmer water sediments from gondwana and elsewhere we term this global warming the boda event

export of nutrients from the arctic ocean 1 this study provides the first physically based mass balanced transport estimates of dissolved inorganic nutrients nitrate phosphate and silicate for the arctic ocean using an inverse model generated velocity field in combination with a quasi synoptic assemblage of hydrographic and hydrochemical data we quantify nutrient transports across the main arctic ocean gateways davis strait fram strait the barents sea opening bso and bering strait we found that the major exports of all three nutrients occur via davis strait transports associated with the east greenland current are almost balanced by transports associated with the west spitsbergen current the most important imports of nitrate and phosphate to the arctic occur via the bso and the most important import of silicate occurs via bering strait oceanic budgets show that statistically robust net silicate and phosphate exports exist while the net nitrate flux is zero within the uncertainty limits the arctic ocean is a net exporter of silicate 15 7 3 2 kmol s 1 and phosphate 1 0 0 3 kmol s 1 net 1 standard error to the north atlantic the export of excess phosphate relative to nitrate from the arctic calculated at 1 1 0 3 kmol s 1 is almost twice as large as previously estimated net transports of silicate and phosphate from the arctic ocean provide 12 and 90 respectively of the net southward fluxes estimated at 47 n in the north atlantic additional sources of nutrients that may offset nutrient imbalances are explored and the relevance and the pathway of nutrient transports to the north atlantic are discussed

reversal of the 1960s to 1990s freshening trend in the northeast north atlantic and nordic seas hydrographic time series in the northeast north atlantic and nordic seas show that the freshening trend of the 1960s 1990s has completely reversed in the upper ocean since the 1990s temperature and salinity have rapidly increased in the atlantic inflow from the eastern subpolar gyre to the fram strait in 2003 2006 salinity values reached the previous maximum last observed around 1960 and temperature values exceeded records the mean properties of the atlantic inflow decrease northwards but variations seen in the eastern subpolar gyre at 57 n persist with the same amplitude and pattern along the pathways to fram strait time series correlations and extreme events suggest a time lag of 3 4 years over that distance this estimate allows predictions to be made the temperature of atlantic water in the fram strait may start to decline in 2007 or 2008 salinity a year later but both will remain high at least until 2010

tide mediated warming of arctic halocline by atlantic heat fluxes over rough topography atlantic water brings heat to the subsurface arctic ocean pan arctic microstructure measurements of energy dissipation suggest that vertical mixing is substantial over the continental slopes tidally induced and insensitive to sea ice cover

arctic ocean warming and its consequences for the denmark strait overflow 1 two anomalously warm inflow pulses into the atlantic water layer of the arctic ocean have occurred since the late 1980s as a consequence temperatures of the arctic basins at 200 800 m depth have increased considerably in comparison to earlier decades the warm inflow pulses also had a low density owing to the decadal time scale of the circulation in the atlantic water layer large pools of anomalously light water have thereby formed in the arctic ocean these will slowly drain back south into the nordic seas we submit that they will be able to influence the overflows into the atlantic across the greenland scotland ridges the atlantic meridional overturning is fed by these overflows our model experiments indicate that the low density anomalies from the arctic ocean may be able to reduce the denmark strait overflow 15 25 years after the entrance of the original signal through fram strait into the arctic ocean the actual size of the reduction depends on the exact path and speed of the anomalies inside the arctic proper and on local processes in the arctic ocean and the nordic sea

along slope variability of barotropic transport in the nordic seas simplified dynamics tested against observations 1 the present study combines simple geostrophic considerations and observational data to examine the along slope evolution of the barotropic transport following the continental slope in the nordic seas and arctic ocean following geostrophic theory the transport evolution is calculated from bottom densities in five different transects within the nordic seas this theoretically predicted transport evolution is compared with transports estimated directly from velocity measurements between the faroe shetland channel and the svinoy section off southern norway across the fram strait below 800 m and between the fram strait and the greenland sea the agreement is generally good between geostrophic theory and observations this indicates that many aspects of the barotropic flow in these regions are captured by geostrophic dynamics between the eastern and western fram strait above 800 m and between svinoy and the eastern fram strait the observed flow fields differ to a large extent from the flow field predicted by geostrophic dynamics indicating that ageostrophic dynamics play a more important role in these regions the barotropic transport differences between the eastern and western fram strait contain information about the barotropic transport evolution along the entire arctic continental slope the good agreement between observations and theory across the strait below 800 m therefore indicates that the flow along the deeper part of the arctic continental slope is well described by geostrophic dynamics according to our results the noticeably more baroclinic nature of the flow in the western fram strait compared with the eastern strait can then be ascribed to water mass modifications along the arctic continental slope

observed sources and variability of nordic seas overflow the overflows from the nordic seas maintain the deep branch of the north atlantic circulation that is an important part of the global climate system an analysis of observed ocean temperatures and salinities between 1950 and 2005 shows that the atlantic water circulating in the nordic seas is the main source for change in the overflow waters

geographical variability of the first baroclinic rossby radius of deformation global 1 83 18 climatologies of the first baroclinic gravity wave phase speed c1 and the rossby radius of deformation l1 are computed from climatological average temperature and salinity profiles these new atlases are compared with previously published 5 83 58 coarse resolution maps of l1 for the northern hemisphere and the south atlantic and with a 1 83 18 fine resolution map of c1 for the tropical pacific it is concluded that the methods used in these earlier estimates yield values that are biased systematically low by 5 15 owing to seemingly minor computational errors geographical variations in the new high resolution maps of c1 and l1 are discussed in terms of a wkb approximation that elucidates the effects of earth rotation stratification and water depth on these quantities it is shown that the effects of temporal variations of the stratification can be neglected in the estimation of c1 and l1 at any particular location in the world ocean this is rationalized from consideration of the wkb approximation

application of bryozoan zoarial growth form studies in facies analysis of non tropical carbonate deposits in new zealand abstract the fragmental remains of bryozoan colonies are the dominant skeletal contributor in many modern and ancient occurrences of non tropical shelf carbonate deposits the taxonomic complexity of the bryozoa the difficulties of systematic classification except by specialists the wide range of particle sizes and of preservation state in the carbonate deposits and the often well cemented nature of host limestones all limit the sedimentological interpretation of the commonly diverse bryozoan component however following the pioneer work of stach in the 1930 s the potential exists for sedimentologists to obtain useful paleo environmental information about the deposits by recording simply the nature and relative abundances of the various growth shapes of the bryozoan material known as their zoarial colonial growth forms here we propose a simple descriptive terminology covering both cheilostome and cyclostome bryozoans that involves four main growth forms encrusting erect rigid erect flexible and free living and a selection of subcategories based on shape identification of these habitat related growth form types is aided by reference to line drawings specimen photographs and photomicrographs of thin section slices the scheme is illustrated by examining briefly some possible environmental controls on the spatial and or time variations in the nature and distribution of colonial growth forms in several examples of modern and tertiary bryozoan dominated carbonate deposits in new zealand we anticipate that the routine description and quantification of bryozoan colonial growth types in non tropical carbonates generally will facilitate the recognition and interpretation of contrasting sub facies within the global foramol bryomol group of carbonate deposits

pre hirnantian latest ordovician benthic community assemblages controls and replacements in a siliciclastic dominated platform of the eastern anti atlas morocco lower middle ashgill sedimentary strata from the mediterranean region have recorded a key episode of temperate to cold water carbonate productivity predating the onset of the hirnantian glaciation the latitudinal position of the moroccan margin of north gondwana during ashgill should have been adequate for the recorded development of carbonate factories however carbonate productivity was neither homogeneous nor laterally persistent as documented in the eastern anti atlas whereas in the erfoud area the bryozoan dominated limestones of the ashgill khabt el hajar formation indicate the intensive activity of carbonate factories these were dramatically reduced in the tiskaouine and gaiz jbels alnif area ca 100 km to the wsw of erfoud in alnif the caradoc ashgill transition lies within the ktaoua group which represents a siliciclastic dominated platform partly truncated by the hirnantian glaciogenic unconformity there three distinct carbonate factories are recognized across the caradoc ashgill transition and early mid ashgill times primarily controlled by accommodation space distance from source areas and subsequent siliciclastic input and benthic community replacements i quiescent episodes of prograding sandy shoals are indicated by a distinct assemblage of epibenthic to quasi endobenthic brachiopods heterorthids drabovids and rafinesquinids and non pelmatozoan echinoderms sphaeronitids and aristocystitids that colonized inclined foresets ii bryozoan thickets rich in robust and delicate branching and encrusting growth forms flourished on carbonate substrates of the distal offshore parts of the platform during major flooding episodes and iii stratigraphically condensed densely fossiliferous phosphatized coquinas display peaks in biodiversity patterns as they are rich in epibenthic rhynchonellid heterorthid and rafinesquinid brachiopods calymenid dalmanitid cheirurid and illaenid trilobites sinuitid eotomariid and holopeid gastropods and hyolithids other episodic and environmentally restricted carbonate factories developed on the alnif mixed platform but are incompletely constrained due to the allochthonous character of their benthic pelagic assemblages which are ecologically mixed due to the effects of continuous shallow water erosive reworking and taphonomically complex histories these shelly carbonate factories allow recognition of the dominant benthic community assemblages that predated the onset of the hirnantian glaciation on this part of the moroccan margin of north gondwana

experiments on bed configurations in fine sands under bidirectional purely oscillatory flow and the origin of hummocky cross stratification abstract we made experiments on bed configurations in bidirectional purely oscillatory flows at a wide range of oscillation periods t and maximum orbital velocities um in two closed flow ducts 0 1 m and 0 4 m wide the motivation was that understanding of bed configurations in oscillatory flows with long periods and high velocities during storm induced deposition in the shallow ocean is needed for interpreting the stratification in such deposits the ripples produced were classified geometrically as two dimensional 2d or three dimensional 3d in plan view geometry and dynamically as oscillatory current ripples dependent upon the patterns of flow and sediment transport specific to the existence of the oscillation itself and reversing current ripples dependent on he existence of the current in one direction or the other during the oscillation runs in the small duct with effectively 0 19 mm and 0 30 mm sand showed the familiar small 2d oscillatory current ripples at short t and low um passing into much larger ripples with spacing up to 2 m at periods of 6 20 s and velocities up to 1 m s with no apparent limit on size with increasing t and um even in such a narrow duct there was some evidence of 3d geometry of the large ripples runs in the large duct with effectively 0 11 mm sand at a single period of about 9 5 s showed a progression from small 2d oscillatory current ripples through small 3d reversing current ripples to large round crested 3d oscillatory current ripples with prominent superimposed 3d to 2d reversing current ripples the large 3d ripples which increased in spacing to 1 3 m at the h ghest attainable um of 1 m s shifted in position and changed in size with time seemingly at random causing substantial local and temporary erosion and deposition at a given point on the bed there was no net aggradation during the runs but a deposit was synthesized by taking a time series of sidewall bed profiles during a run in which large 3d ripples developed from an initially plane bed and changed irregularly in size and position as they grew toward equilibrium and then plotting the profiles one above the previous with a constant upward increment the resulting stratification is strikingly similar to much hummocky cross stratification in ancient sandstones this suggests that some hummocky cross stratification is generated during sediment fallout from strong purely oscillatory flows at moderate to long oscillation periods as large 3d oscillatory current bed forms develop from a planar bed during strong but waning flow

sources of eddy kinetic energy in the labrador sea experiments with a suite of north atlantic general circulation models are used to examine the sources of eddy kinetic energy eke in the labrador sea a high resolution model version 112 quantitatively reproduces the observed signature a particular feature of the eke in the labrador sea is its pronounced seasonal cycle with a maximum intensity in early winter as already found in earlier studies based on altimeter data in contrast to a previously advanced hypothesis the seasonally varying eddy field is not related to a forcing by high frequency wind variations but can be explained by a seasonally modulated instability of the west greenland current wgc the main source of eke in the labrador sea is an energy transfer due to reynolds interaction work barotropic instability in a confined region near cape desolation where the wgc adjusts to a change in the topographic slope geostrophic contours tend to converge upstream of cape desolation such that the topographically guided wgc narrows as well and becomes barotropically unstable the eddies spawned from the wgc instability area dominating the eke in the interior labrador sea are predominantly anticyclonic with warm and saline cores in the upper kilometer of the water column while the few cyclones originating as well from the instability area show a more depth independent structure companion experiments with a model exhibit the strength of the wgc influenced by either changes in the wind stress or heat flux forcing as a leading factor determining seasonal to interannual changes of eke in the labrador sea

oceanic isopycnal mixing by coordinate rotation abstract current numerical models of oceanic circulation differentiate between the eddy diffusion and viscosity transport along the geopotential horizontal and vertical directions only in order to model the effect of anisotropic turbulence as diffusive transport along and across density surfaces the isopycnal mixing tensor has been transformed from a diagonal second rank tensor in the isopycnal coordinate system to a tensor containing off diagonal elements in the geopotential coordinate system

vertical movements along the northern border of the west african craton the reguibat shield and adjacent basins the absence of a sedimentary record on large cratonic areas often prevents the reconstruction of the history of their vertical movements the reguibat rise belonging to the west african craton is typically a large basement high whose meso cenozoic history is poorly known because of the extreme reduction of this sedimentary record in this paper we present the first thermochronological data from the centre of the reguibat rise and combine them with the geometry of the sedimentary formations in the adjoining tindouf and taoudeni basins situated north and south respectively fission track analysis on apatite yields ages from 256 21 ma to 139 8 ma and 120 10 ma by u th he dating two competing scenarios are tested based on these data with thermal history modelling we favour the scenario that includes a late jurassic early cretaceous cooling of the samples based on stratigraphical constraints and the thermochronological results we then propose a new model for the evolution of this region and reveal the occurrence of a previously unknown major exhumation event at the jurassic cretaceous transition accounting for the main present day structures

evolution of a permian intraoceanic arc trench system in the solonker suture zone central asian orogenic belt china and mongolia abstract the identification of a fossil arc trench system from the ophiolite decorated solonker suture zone in the southernmost central asian orogenic belt caob enables us to constrain the timing of pre subduction extension ca 299 290 ma subduction initiation ca 294 280 ma ridge trench collision ca 281 273 ma and slab break off ca 255 248 ma in the permian a fraction of proto arc crust ca 45 km long up to 8 km wide is preserved as a volcanic plutonic sequence and is juxtaposed against a wide ca 30 80 km forearc melange this proto arc crust comprises two distinct magma series island arc tholeiite iat and mid ocean ridge basalt morb both of which have strong supra subduction zone ssz geochemical signatures zircons from a gabbro and a plagiogranite yielded weighted mean 206pb 238u ages of 284 0 4 0 and 288 0 6 0 ma the forearc melange consists of numerous ophiolite fragments and continental margin derived olistoliths blocks that predate the ophiolite the olistoliths are best represented by a gabbroic block 291 8 2 3 ma that contains granite xenoliths 312 6 1 8 and 313 6 3 1 ma other dated blocks include a trondhjemite 323 9 2 7 ma a gabbro 296 6 1 7 ma and a tonalite 294 9 2 4 ma small bodies of diabase andesite and diorite in the forearc melange exhibit a wide variety of geochemical signatures we dated zircons from an n morb like diabase 274 4 2 5 ma an e morb like diabase 252 5 2 3 ma a transitional sanukitoid adakite andesite 250 2 2 4 ma a sanukitoid high mg diorite 251 8 1 1 ma and an anorthosite 252 2 1 7 ma the n morb like diabase contains ca 301 394 ma zircon xenocrysts suggesting assimilation of trench sediments when a spreading ridge intersected a trench the other dated rocks simultaneously formed near the permian triassic boundary and captured abundant zircon xenocrysts ca 269 295 ma ca 301 495 ma and ca 923 2501 ma our new formation ages constrain a magmatic episode in response to slab break off beneath a fossil forearc in a young post collisional setting and the youngest xenocryst ages ca 269 273 ma may define the maximum depositional age of trench sediments

integrated brachiopod based bioevents and sequence stratigraphic framework for a late ordovician subpolar platform eastern anti atlas morocco the upper ordovician katian hirnantian brachiopods of tafilalt eastern anti atlas are locally abundant diverse and well preserved providing a near continuous record of faunal change on a high latitude siliciclastic dominated platform a chronostratigraphic framework based on brachiopod distribution and preservation in shell accumulation events and integrated with sequence stratigraphy has been generated for the katian interval which has allowed correlation with the chitinozoan based chronostratigraphic and sequence stratigraphic framework erected for the central anti atlas in tafilalt two katian transgressive regressive composite depositional sequences c 60 and 170 m thick and related to third order fluctuations in sea level were unaffected by hirnantian glaciogenic erosion they were deposited on a mixed platform with a bryonoderm association dominated by brachiopods bryozoans and echinoderms brachiopods developed in high energy inner shelf areas whereas bryozoans mainly trepostomates and fenestrates and pelmatozoans cystoids and crinoids dominated in low energy outer shelf areas brachiopod accumulations mark distinct event surfaces such as lag and event concentrations hydraulic simple and composite concentrations related to transgressive surfaces and hiatal condensed concentrations marking maximum flooding surfaces the taphonomic condensation displayed by the hirnantian alnif member which onlaps the erosive base of glaciogenic tunnel channels is explained as reworking and resedimentation of allochthonous robust biogenic hard parts sourced from the underlying katian ktaoua group

late paleozoic early mesozoic magmatic history of central inner mongolia china implications for the tectonic evolution of the xingmeng orogenic belt the southeastern segment of the central asian orogenic belt abstract the tectonic setting and location of the southernmost boundary of the central asian orogenic belt caob in the late paleozoic early mesozoic era and the history evolution for the xingmeng orogenic belt xmob are sources of debate within the scientific community this paper presents new geochronological petrological and geochemical data for late paleozoic early mesozoic intrusions from the siziwangqi region in the southeastern caob and discusses the tectonic setting for that area using zircon la mc icpms u pb dating intrusions can be broadly grouped as late carboniferous amphibolite with an age of 323 1 3 4 ma middle late permian granitoids with ages of 271 3 1 5 ma 261 3 3 8 ma 260 6 4 8 ma 259 9 3 5 ma 253 3 4 8 ma and 249 6 4 8 ma early triassic k feldspar granite with an age of 235 0 1 8 ma these studies by interaction of regional geology provide new constraints on the tectonic evolution of the southeastern central asian orogenic belt during the late paleozoic early mesozoic and we predict five stages of tectonic evolution during the late paleozoic early mesozoic 1 the early carboniferous early permian 298 ma which is the active continental margin stage and the exit of the back arc basin during the late carboniferous 2 the early permian middle permian 298 271 ma where there was continued subduction of paleo asian oceanic lithosphere and the solonker ophiolite emplacement at the end of early permian 3 the middle permian 271 261 ma which had continent continent collision between the siberian plate and the north china craton 4 the middle permian middle triassic 261 235 ma which was the collisional orogeny stage with few intermountain basin deposition and the disappearance of marine strata and 5 late triassic

gondwana derived microcontinents the constituents of the variscan and alpine collisional orogens abstract the european variscan and alpine mountain chains are collisional orogens and are built up of pre variscan building blocks which in most cases originated at the gondwana margin such pre variscan elements were part of a pre ordovician archipelago like continental ribbon in the former eastern prolongation of avalonia and their present day distribution resulted from juxtaposition through variscan and or alpine tectonic evolution the well known nomenclatures applied to these mountain chains are the mirror of variscan resp alpine organization it is the aim of this paper to present a terminology taking into account their pre variscan evolution at the gondwana margin they may contain relics of volcanic islands with pieces of cadomian crust relics of volcanic arc settings and accretionary wedges which were separated from gondwana by initial stages of rheic ocean opening after a short lived ordovician orogenic event and amalgamation of these elements at the gondwanan margin the still continuing gondwana directed subduction triggered the formation of ordovician al rich granitoids and the latest ordovician opening of palaeo tethys an example from the alps external massifs illustrates the gradual reworking of gondwana derived pre variscan elements during the variscan and alpine tertiary orogenic cycles

oceanic circulation as an element in palaeogeographical reconstructions the arenig early ordovician as an example a new conceptual palaeo oceanographical model is outlined in this paper the model differs from previous models by using shifts in hadley circulation caused by orbital variations and the rotation rate of the earth to locate the position of the planetary oceanic low and high pressure systems around which the planetary ocean surface currents flow adapting the model to the arenig early ordovician the temperate low pressure zones were found to be located at 50 latitude and the subtropical high pressure zones at 25 latitude traditionally most palaeozoic palaeogeographical recon structions are reconstructed using palaeomagnetic data supplemented with data from climate sensitive lithofacies and palaeo biogeographical distributions however as a new approach in palaeogeographical reconstructions the con ceptual palaeo oceanographical model is combined with palaeobiogeographical data for the arenig series comple menting the palaeomagnetic data and resulting in a new refined palaeogeographical reconstruction

global ocean surface velocities from drifters mean variance el nino southern oscillation response and seasonal cycle 1 global near surface currents are calculated from satellite tracked drogued drifter velocities on a 0 5 0 5 latitude longitude grid using a new methodology data used at each grid point lie within a centered bin of set area with a shape defined by the variance ellipse of current fluctuations within that bin the time mean current its annual harmonic semiannual harmonic correlation with the southern oscillation index soi spatial gradients and residuals are estimated along with formal error bars for each component the time mean field resolves the major surface current systems of the world the magnitude of the variance reveals enhanced eddy kinetic energy in the western boundary current systems in equatorial regions and along the antarctic circumpolar current as well as three large eddy deserts two in the pacific and one in the atlantic the soi component is largest in the western and central tropical pacific but can also be seen in the indian ocean seasonal variations reveal details such as the gyre scale shifts in the convergence centers of the subtropical gyres and the seasonal evolution of tropical currents and eddies in the western tropical pacific ocean the results of this study are available as a monthly climatology

early paleozoic magmatic history of central inner mongolia china implications for the tectonic evolution of the southeast central asian orogenic belt to provide insights into the early paleozoic tectonic evolution of the southern portion of the long lived central asian orogenic belt we have conducted major and trace element analyses and zircon u pb dating of granitoid samples from central inner mongolia our study area covers three pre mesozoic tectonic units from north to south the wenduermiao subduction accretionary complex the bainaimiao magmatic belt and the northern margin of the north china craton our new geochronological and geochemical data show the temporal and genetic relationships between the three tectonic units accordingly we suggest that the wenduermiao subduction accretionary complex developed in the middle cambrian late silurian 509 421 ma comprising of coeval oceanic crust arc magmatism and forearc deposits the bainaimiao continental arc was developed during the late cambrian to early silurian 501 437 ma which superposed on the basement with the affinity of the north china craton the back arc basin opened prior to early silurian and lasted to the late silurian which is slightly younger than bainaimiao island arc the wenduermiao ocean between the wenduermiao subduction accretionary complex and the bainaimiao continental arc existed in early paleozoic

observed and modeled surface eddy heat fluxes in the eastern nordic seas large scale budget calculations and numerical model process studies suggest that lateral eddy heat fluxes have an important cooling effect on the norwegian atlantic current nwac as it flows through the nordic seas but observational estimates of such fluxes have been lacking here wintertime surface eddy heat fluxes in the eastern nordic seas are estimated from surface drifter data satellite data and an eddy permitting numerical model maps of the eddy heat flux divergence suggest advective cooling along the path of the nwac integrating the flux divergence over temperature classes yields consistent estimates for the three data sets the waters warmer than about 6 c are cooled while the cooler waters are warmed similar integrations over bottom depth classes show that regions shallower than about 2000 m are cooled while deeper regions are warmed finally integrating the flux divergence along the core of the nwac suggests that the highest eddy induced heat loss at the surface is along the steepest part of the continental slope east of the lofoten basin the model fields indicate that cooling of the current by lateral eddy fluxes is comparable to or larger than the local heat loss to the atmosphere

on the structure of the lofoten basin eddy 1 a small anticyclonic eddy of extraordinary intensity sits in the center of the lofoten basin near 69 40 n 3 e this paper gives a first detailed description of its kinematics and lowest order dynamic balances using a 75 khz vessel mounted acoustic doppler current profiler hydrography and six rafos floats to probe the eddy we document a solid body core with 7 8 km radius and relative vorticity very close to f where f is the local coriolis parameter maximum orbital velocities close to 0 8 ms 1 were observed at 18 km radius one float trapped in the core of the eddy for 9 months indicated undiminished strength throughout that period possibly even intensifying in winter hydrography revealed adiabatic conditions from the bottom of a shallow seasonal thermocline to 1000 m depth in early july 2010 thermal convection in winter maintains an already deep pycnostad and may also play a key role in intensifying the eddy quite possibly through penetrative convection that deepens and sharpens the underlying pycnocline heat lost to the atmosphere has to be replenished from warm anticyclonic eddies shed off the eastern branch of the norwegian atlantic current but the mechanism s by which it is added to the eddy remains to be studied examination of historical data sets suggests the eddy is a permanent feature of the lofoten basin two hydrocasts from the 1960s also show a similar adiabatic mixed layer albeit 1 c cooler than in 2010 perhaps reflecting the generally cold winter conditions that prevailed then

eddy driven recirculation of atlantic water in fram strait eddy resolving regional ocean model results in conjunction with synthetic float trajectories and observations provide new insights into the recirculation of the atlantic water aw in fram strait that significantly impacts the redistribution of oceanic heat between the nordic seas and the arctic ocean the simulations confirm the existence of a cyclonic gyre around the molloy hole near 80 n suggesting that most of the aw within the west spitsbergen current recirculates there while colder aw recirculates in a westward mean flow south of 79 n that primarily relates to the eastern rim of the greenland sea gyre the fraction of waters recirculating in the northern branch roughly doubles during winter coinciding with a seasonal increase of eddy activity along the yermak plateau slope that also facilitates subduction of aw beneath the ice edge in this area

non tropical carbonate deposits on the modern new zealand shelf abstract extensive ca 50 000 km 2 shallow marine platforms 70 caco 3 despite proximity to a tectonically active plate margin in these regions the terrigenous sediment supply is presently low and growth of epibenthos is fostered by firm substrates rock gravels shells seaweeds and the generally energetic nature and high nutrient levels of open shelf waters rapid transition into adjacent terrigenous dominated facies is characteristic irrespective of water depth the carbonates are coarse grained and fragmental carbonate mud is rare calcite dominates over aragonite high mg calcite widespread off northern new zealand is rare in the south skeletal material is dominated by bryozoans and bivalve molluscs with significant local contributions from foraminifers barnacles calcareous red algae and echinoderms the name bryomol is suggested for this distinctive temperate region skeletal carbonate facies which can be usefully subdivided based on dominant zoarial growth forms of the bryozoan component known to be habitat related bioerosion is an important mechanism of skeletal fragmentation and degradation many grains especially aragontic bivalves are infested by endolithic borers and have low preservation potential ages of skeletal material in the surficial deposits range from more than 20 000 years b p to modern which is consistent with both low rates of carbonate production and sediment accumulation and the wide range in preservation state of grains some data suggest that the skeletal carbonates are dispersed and mixed mainly during infrequent movement of sand ribbons sand waves and sand sheets driven by storm assisted tidal flows tracts of modern palimpsest and relict carbonates can occur in juxtaposition the facies characteristics of the new zealand shelf carbonate deposits contrast significantly with those of the classical bahaman type carbonate model however they are similar to those reported from many other mid to high latitude carbonate shelves and afford good analogues for most onland occurrences of new zealand cenozoic limestones

a late ordovician phreatomagmatic complex in marine soft substrate environment the crozon volcanic system armorican massif france the mafic lavas and the diabases of crozon armorican massif france belong to an anorogenic ordovician volcanic complex emplaced on a rifted passive margin in north gondwana magma passed through syn volcanic soft sedimentary substrate which is today mostly composed of alternating sandstones and mudstones from llanvirn to ashgill in age field observations together with microscopic studies and geochemical analyses of magmatic rocks lead us to propose a model of volcano formation which combines hydromagmatic processes peperitic intrusions a shallow submarine tephra settling eruption fed turbidity currents and a pillow lava effusion the crozon outcrops can be used to reconstruct a complete cross section from the root of the volcanic complex to the lavas and breccias emplaced on the sea floor the sites expose i a hypabyssal breccia containing mud chunks and coarse grained diabase clasts with amoeboidal fine grained magmatic material ii bulbous peperitic sills and pillow like lobes bearing a great quantity of sediment derived enclaves of fluidal morphology iii volcaniclastic breccias containing near spherical magmatic clasts that resulted from the complete fragmentation of sills in the ductile regime iv a rhythmic peperitic breccia interpreted as the product of mingling between thin lava flows and soft calcareous sediment the crozon volcanic form resulting from explosive interaction with subsurface surface water was probably a subaqueous collapsed tuff cone this upper part of the system is synchronous with an ashgill carbonate sedimentation which overlies an ordovician siliciclastic succession deposited in shelf environments

recirculation of atlantic water in the western barents sea 1 in this article the atlantic inflow with the north cape current to the barents sea and potential recirculation of this water in the bear island trough is investigated this is resolved by combining continuous current meter and repeated hydrographic section data in the barents sea opening the estimated annual mean net fluxes when excluding the contribution from the norwegian coastal current are 1 1 sv and 39 tw estimated relative to a reference temperature of 0 c the estimated heat flux associated with the outflow in the bear island trough is relatively large 12 tw long term current meter records do not show a close relationship between variations in the inflow and the outflow one year low pass filtered variations in temperature and salinity of the outflowing waters in the bear island trough are positively correlated with variations of the inflowing atlantic water with a lag of about seven months on the basis of a simple mixing model the outflow water consists of about 80 atlantic water that is additionally cooled by 2 0 2 5 c by heat loss to the atmosphere by considering the relative weak mean currents in this region it can be inferred that the fraction of the atlantic water that recirculates follows a relatively short pathway in the bear island trough before returning to the norwegian sea

subglacial to proglacial depositional environments in an ordovician glacial tunnel valley alnif morocco abstract this paper presents the sedimentary analysis of an exceptional ordovician glacial tunnel valley in the eastern part of the anti atlas the valley infill comprises two major glacial erosion surfaces striated pavements each overlain by a fining upward glacial unit these units are composed of five distinct facies associations recording the evolution from subglacial to proglacial environments and an additional sixth facies association overtopping the tunnel valley infill and associated with post glacial environments the tunnel valley infill also records a transitional environment between the subglacial and proglacial settings which is compared with the antarctic ice sheet margin these three environments are defined by the position of the grounding line and the coupling line the new proposed depositional model also differs from usual ordovician depositional models in which the main tunnel valley infill is interpreted as essentially proglacial outwash deposits in a range of glaciomarine to glaciofluvial environments overall a substantial part of the valley infill 50 of volume was deposited in a subglacial setting the sedimentary bodies could form potentially thick and laterally extended although these were limited by the shape and extent of the subglacial accommodation space finally the sedimentary record when compared with regional analogues also provides information for the palaeogeographic reconstruction of the ordovician ice sheet in this region

winter convection transports atlantic water heat to the surface layer in the eastern arctic ocean a 1 yr 2009 10 record of temperature and salinity profiles from ice tethered profiler itp buoys in the eurasian basin eb of the arctic ocean is used to quantify the flux of heat from the upper pycnocline to the surface mixed layer the upper pycnocline in the central eb is fed by the upward flux of heat from the intermediate depth 150 900m atlanticwater aw layer thisfluxisestimatedtobe 1wm 22 averaged over one year release of heat from the upper pycnocline through the cold halocline layer to the surface mixed layer is however seasonally intensified occurring more strongly in winter this seasonal heat loss averages 3 4wm 22 between january and april reducing the rate of winter sea ice formation this study hypothesizes that the winter heat loss is driven by mixing caused by a combination of brine driven convection associated with sea ice formation and larger vertical velocity shear below the base of the surface mixed layer sml enhanced by atmospheric storms and the seasonal reduction in density difference between the sml and underlying pycnocline

observations of the labrador sea eddy field this paper is an observational study of small scale coherent eddies in the labrador sea a region of dense water formation thought to be of considerable importance to the north atlantic overturning circulation numerical studies of deep convection emphasize coherent eddies as a mechanism for the lateral transport of heat yet their small size has hindered observational progress a large part of this paper is therefore devoted to developing new methods for identifying and describing coherent eddies in two observational platforms current meter moorings and satellite altimetry details of the current and water mass structure of individual eddy events as they are swept past by an advecting flow can then be extracted from the mooring data a transition is seen during mid 1997 with long lived boundary current eddies dominating the central labrador sea year round after this time and convectively formed eddies similar to those seen in deep convection modeling studies apparent prior to this time the topex poseidon altimeter covers the labrador sea with a loose net of observations through which coherent eddies can seem to appear and disappear by concentrating on locating and describing anomalous events in individual altimeter tracks a portrait of the spatial and temporal variability of the underlying eddy field can be constructed the altimeter results reveal an annual pulsation of energy and of coherent eddies originating during the late fall at a particular location in the boundary current pinpointing the time and place of the boundary current type eddy formation the interannual variability seen at the mooring is reproduced but the mooring site is found to be within a localized region of greatly enhanced eddy activity notably lacking in both the annual cycle and interannual variability is a clear relationship between the eddies or eddy energy and the intensity of wintertime cooling these eddy observations as well as hydrographic evidence suggest an active role for boundary current dynamics in shaping the energetics and water mass properties of the interior region

palaeozoic low oxygen high latitude carbonates silurian and lower devonian nautiloid and scyphocrinoid limestones of the anti atlas morocco abstract high latitude silurian and lowermost devonian basinal limestones of northern gondwana are characterised by mass accumulations of orthocone nautiloids bivalves and planktonic crinoids scyphocrinoids extensive exposures in the anti atlas of morocco reveal this basinal facies passes up gradient into an iron rich bioclastic facies associated with distal shelf siliciclastics and into crinoid brachiopod dominated bioclastic blankets and shoals the limestones formed in a cool water setting in which upwelling of nutrient rich waters during sea level lowstands is interpreted to have triggered the abundance of nautiloids and scyphocrinoids preservation of organic matter in under and overlying graptolite shales as well as iron precipitation in the neighbouring shallower water sub oxic zone the nautiloid limestones proved to be good correlation markers on a regional to global scale contemporaneous siliciclastic supply into the neighbouring facies belt as well as new biostratigraphic data are taken as evidence that these limestones can be correlated to 2nd order eustatic sea level lowstands and the following transgression the low oxygen basinal facies disappeared more or less abruptly during the early devonian pragian and was replaced by a well oxygenated basinal lowstand facies suggesting the end of upwelling at the same time the first reefal build ups coral biostromes and mud mounds appear in north africa indicating a significant rise in water temperatures the change from low oxygen lowstand mass accumulations to well oxygenated basinal facies with a concomitant rise in water temperature is in accordance with recent models of a cool silurian to earliest devonian lochkovian ocean with oscillating oxic to anoxic ventilated to poorly circulated oceanic states and a warm ocean with anoxic to euxinic poorly ventilated to stagnant ocean waters from the beginning of the pragian onwards

eddy kinetic energy in the arctic ocean from a global simulation with a 1 km arctic simulating arctic ocean mesoscale eddies in ocean circulation models presents a great challenge because of their small size this study employs an unstructured mesh ocean sea ice model to conduct a decadal scale global simulation with a 1 km arctic it provides a basinwide overview of arctic eddy energetics increasing model resolution from 4 to 1 km increases arctic eddy kinetic energy eke and total kinetic energy tke by about 40 and 15 respectively eke is the highest along main currents over topography slopes where strong conversion from available potential energy to eke takes place it is high in halocline with a maximum typically centered in the depth range of 70 110 m and in the atlantic water layer of the eurasian basin as well the seasonal variability of eke along the continental slopes of southern canada and eastern eurasian basins is similar stronger in fall and weaker in spring

circulation and transformation of atlantic water in the eurasian basin and the contribution of the fram strait inflow branch to the arctic ocean heat budget abstract the inflows of atlantic water from the nordic seas to the arctic ocean through fram strait and over the barents sea are examined and their pathways and transformations in the eurasian basin are described based primarily on hydrographic observations from two cruises with rv polarstern in 2007 and 2011 the contrast between the high salinity atlantic water core in the nansen basin and the lower atlantic water salinity in the amundsen basin combined with a salinity minimum below the atlantic layer suggest that the fram strait branch mainly remains in the nansen basin while the barents sea branch continues along the continental slope enters the amundsen basin and provides most of the atlantic water in the makarov and canada basins to examine the consequences of such a circulation pattern recently published estimates of the in and outflows of volume and liquid freshwater through the barents sea bering strait and the canadian arctic archipelago as well as river runoff net precipitation and ice export are reviewed and added together to achieve volume and freshwater balances net outflows through fram strait of 2 3 sv and 100 msv respectively are required this is reasonably close to the recently reported fram strait transport estimates the net outflows are separated into two parts upper layer transports less dense than the entering atlantic water and lower layer transports as dense as or denser than the atlantic water the largest net volume outflow occurs in the lower layer 1 65 sv while the liquid freshwater is almost exclusively exported in the 0 64 sv net outflow in upper layer leading to unrealistically low salinities in the upper layer compared with observations atlantic water is north of svalbard transformed into less saline surface water through melting of sea ice which can supply the necessary higher salinity halocline water to the upper layer 1 23 sv of halocline water of salinity 34 2 must be added to obtain a more realistic salinity of 33 1 leading to a total export of 1 84 sv upper layer water in the east greenland current existing observations of the net transports into and out of the arctic ocean through fram strait in different temperature classes are used to estimate the heat loss of the atlantic water entering the arctic ocean through fram strait about 10 tw are supplied to the atmosphere in addition to the loss of 24 tw occurring in connection with the formation of the halocline water if the hypothesis that the fram strait branch remains in the nansen basin is true it implies a heat loss between 5 and 15 w m 2 in the nansen basin depending upon how much heat is temporarily stored in the water column this is high compared to the 2 w m 2 commonly cited as the ocean heat flux to the atmosphere in the arctic ocean

great salinity anomalies in the north atlantic abstract we revisited the great salinity anomaly of the 1970s gsa 70s dickson et al 1988 and documented the newly identified great salinity anomaly of the 1980s hence termed gsa 80s both propagated around the north atlantic in a similar fashion the advective mechanism initially proposed to explain the observed sequence of low salinity low temperature events during the gsa 70s apparently holds also for the gsa 80s the latter was successively observed in the west greenland current 1982 the labrador current 1983 the flemish pass 1984 near the charlie gibbs fracture zone 1984 1985 in the rockall channel 1985 south of iceland 1985 1988 in the north sea 1986 1987 norwegian sea 1987 1988 barents sea 1988 1989 and iceland sea 1989 1990 the advection speed of the gsa 80s seems to be greater than the one of the gsa 70s the 1980s anomaly reached the barents sea 6 to 7 years after peaking in the west greenland current while the 1970s anomaly traveled the same route in 8 to 10 years these anomalies however seem to be of different origin the gsa 70s was apparently boosted remotely by a freshwater sea ice pulse from the arctic via fram strait consequently the gsa 70s was accompanied by a large sea ice extent anomaly in the greenland and iceland seas which propagated into the labrador sea in contrast the gsa 80s was likely formed locally in the labrador sea baffin bay mainly because of the extremely severe winters of the early 1980s but supplemented with a possible contribution of the arctic freshwater outflow via the canadian archipelago facilitated by strong northerly winds which would have enhanced stability and ice formation this anomaly was also associated with a positive sea ice extent anomaly in the labrador sea baffin bay which however had no upstream precursor in the greenland sea thus the gsas are not necessarily caused solely by an increased export of freshwater and sea ice from the arctic via fram strait these results are corroborated by the early 1990s data when a new fresh cold anomaly was formed in the labrador sea and accompanied by a large positive sea ice extent anomaly the harsh winters of the early 1990s were however confined to the labrador sea baffin bay area while the atmospheric and oceanic conditions in the greenland iceland and irminger seas were normal the labrador sea baffin bay area appears therefore to play a key role in formation of gsas as well as in propagation of the gsas formed upstream a likely contribution of the enhanced canadian archipelago freshwater outflow to the gsa formation also seems to be significant two major modes of the gsa origin are thus identified remote generated by an enhanced arctic ocean freshwater export via either fram strait or the canadian archipelago and local resulting from severe winters in the labrador sea baffin bay both modes should be taken into account to model decadal variability of the coupled ocean ice atmosphere system in the north atlantic arctic basin

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

width of the north cape current and location of the polar front in the western barents sea 1 earlier results have shown that stronger southwesterly winds give higher temperatures stronger velocities and higher transports in the north cape current ncac in the western barents sea this investigation shows that the wind field causing the stronger southwesterlies also causes a wider ncac i e the ncac becomes warmer and wider at the same time in warm periods the ncac seems to be a two core current system while it has only one wider core in cold periods the reason for the fluctuations in the width of the ncac is a non uniform wind field across the current the varying width of the ncac affects the location of the polar front south of bear island the location of this front is not as stationary as earlier believed and in warm periods with strong wind the front is located further upslope than in cold periods

the great salinity anomaly in the northern north atlantic 1968 1982 the widespread freshening of the upper 500 800m layer of the northern north atlantic which this paper describes represents one of the most persistent and extreme variations in global ocean climate yet observed in this century though a range of explanations have been advanced to explain this event including in situ changes in the surface moisture flux this paper describes the great salinity anomaly as largely though not entirely an advective event traceable around the atlantic subpolar gyre for over 14 years from its origins north of iceland in the mid to late 1960s until its return to the greenland sea in 1981 1982 the overall propagation speed around this subpolar gyre is estimated at about 3cm s 1 of the total salt deficit associated with the anomaly as it passed south along the labrador coast in 1971 1973 about 72 109 tonnes a deficit equivalent to about two thirds of this figure 47 109 tonnes ultimately passed through the faroe shetland channel to the barents sea arctic ocean and greenland sea during the mid 1970s possible effects on deep water formation and on the representativeness of historical section data are discussed

freshwater fluxes in the east greenland current a decade of observations 1 over a decade of mooring measurements in the western fram strait at 78 50 n shows that the annual mean liquid freshwater flux fwf in the east greenland current is relatively constant at 1274 453 km3 yr 1 40 4 14 4 msv despite the fact that the annual mean total volume transport of the egc has more than doubled since 2001 this is shown to be due to an increase of the transport in the deeper ocean and the fact that the largest fw content is present on the east greenland shelf and not in the core of the egc in order to capture the fwf on the shelf modeling results of naosim are included showing that a mean contribution of fwf on the shelf of at least 807 357 km3 yr 1 25 6 11 3 msv should be added to the fwf obtained for the egc when compared to the extra input of freshwater required to account for the 1960 1990 freshening of the northern north atlantic the observed variations in the 1998 2008 egc liquid freshwater fluxes are small

a type granites in northeastern china age and geochemical constraints on their petrogenesis abstract a type granites are widely distributed in northeastern china ne china they were emplaced during three major episodes the permian late triassic to early jurassic and early cretaceous and evolved in different tectonic regimes according to their mineralogical and geochemical characteristics two subgroups of a type granites aluminous and peralkaline can be recognized the peralkaline subgroup contains alkali mafic minerals such as riebeckite arfvedsonite and sodic pyroxene while the aluminous subgroup contains annite and fe rich calcic or sodic calcic amphibole with respect to the aluminous subgroup the peralkaline granites contain higher rb ga and total rare earth elements ree but lower mgo cao al 2 o 3 ba and sr based on the discrimination criteria of eby geology 20 1992 641 the permian and late triassic to early jurassic a type granites belong to the a 2 post orogenic type whereas the early cretaceous granites are of the a 1 anorogenic type nd isotopic compositions of these a type granites indicate their derivation from a dominantly juvenile crustal source their origin is thought to have involved partial melting of an underplated lower crustal source because the generation of a type granites requires high melting temperature we propose models involving slab break off lithospheric delamination and extension the permian a type granites have the same age range as those in eastern junggar southern mongolia and central inner mongolia they occur along a major suture and form a narrow belt between the north china and siberian cratons we suggest that their formation was associated with post collisional slab break off the late triassic to early jurassic a type granites are likely to be the product of lithospheric delamination after the final collision of the major crustal blocks in the late paleozoic to early triassic the early cretaceous a type granites have an anorogenic affinity and were possibly associated with rifting in eastern china at this time associated with the onset of paleo pacific subduction consequently we conclude that the a type granites in ne china were generated at three different times involving multiple processes operative in different tectonic environments

does porewater or meltwater control tunnel valley genesis case studies from the hirnantian of morocco several ordovician tunnel valleys are exposed in the moroccan anti atlas mountains including the alnif and the foum larjamme tunnel valleys located 150 km away from each other sedimentological and deformational analyses of these two glacial troughs reveal that differing processes lead to their formations the alnif tunnel valley contains numerous deformation structures within sediments both below and above the main glacial erosion contact surface ball structures and clastic dykes occur within preglacial sediments down to 35 m below glacial incisions while overlying glacial sediments contain fluted surfaces clastic dykes dewatering structures folds and radial step normal faults the characteristics of the alnif tunnel valley can be explained by a porewater pressure driven model of formation where the localized increase of basal shear stress and porewater pressure underneath subglacial deforming zones lead to the development of a dense hydrofracture network in the preglacial bed these processes of hydraulic brecciation promoted subglacial remobilization of the preglacial material and contributed to the formation of the tunnel valley the foum larjamme tunnel valley displays undisturbed preglacial sediments and few dewatering structures at the base of the glacial sedimentary infill which suggests relatively low porewater pressures within the tunnel valley during formation this second type of tunnel valley where porewater pressure remained relatively low appears to have been formed by meltwater erosion the undulating base of the foum larjamme tunnel valley implies progressive erosion by a stable subglacial braided network of nye channels or alternatively by channels migrating laterally during episodic minor subglacial outbursts these two tunnel valleys highlight the regional variability of processes involved in the formation of tunnel valleys the distribution of palaeo ice streams in north africa illustrate that morphologies and processes involved in the formation of tunnel valleys vary between ice stream and inter ice stream zones due to variations in meltwater availability the topography and bed lithological properties

attributes and origins of ancient submarine slides and filled embayments examples from the gulf coast basin large submarine slides and associated shelf margin embayments represent an intermediate member in the continuum of unstable shelf margin features on seismic profiles they may resemble submarine canyons but are different in their size morphology origin and hydrocarbon exploration potential two large neogene submarine slides located in the northwestern gulf coast basin formed on the upper slope and flanks of prominent shelf margin deltas the basal detachment surface of each slide is a structural discontinuity that may be misinterpreted as an erosional unconformity and therefore misidentified as a stratigraphic boundary separating depositional sequences regional stratigraphic correlations indicate that both slides were initiated after the continental platform wa flooded the condensed sections deposited during the rise in relative sea level contain the basal detachment surfaces beyond these observations the relationships between the slides and sea level fluctuations are uncertain the shelf margin embayments created by the slides apparently were partly excavated during periods of lowered relative sea level and were filled during the subsequent relative sea level rise and highstand eventually the preslide morphology of the shelf margin was restored by coalesced prograding deltas submarine slides exhibit landward dipping wavy mounded and chaotic seismic reflections that are manifestations of slump blocks and other mass transport material composition of these internally derived slide deposits depends on the composition of the preexisting shelf margin embayment fill above the slide consists mostly of externally derived mudstones and sandstones deposited by various disorganized slope processes as well as more organized submarine channel levee systems thickest slope sandstones which are potential hydrocarbon reservoirs commonly occur above the basal slide mudstones where seismic reflections change from chaotic patterns to overlying wavy or subhorizontal reflections