spreading of the western mediterranean deep water after winter 2005 time scales and deep cyclone transport this work is dedicated to the study of the propagation of the western mediterranean deep water wmdw formed in the gulf of lions during the exceptional winter 2005 a simulation of the 1998 2008 period has been carried out with an eddy resolving ocean general circulation model of the mediterranean sea driven by interannual high resolution air sea fluxes this study first presents a validation of the recently improved model configuration against satellite observations then we assess the ability of the model to reproduce the particularly intense deep convection event of winter 2005 in the gulf of lions a huge volume of very dense water is formed in the simulations at that time annual formation rate of about 3 sv the thermohaline characteristics of the new wmdw allow a monitoring of its deep propagation we identify several deep cyclones as mainly responsible of the fast spreading of the wmdw southwards in the western mediterranean by comparing eulerian and lagrangian approaches we estimate different transport times of the wmdw by these cyclonic eddies and compare them to those deduced from several observations finally we argue that these cyclones favour the propagation of the wmdw thermohaline characteristics towards the channel of sardinia and decrease the volume of wmdw which can reach the strait of gibraltar

hydrographic structure of the convection regime in the gulf of lions winter 1987 abstract deep winter convection in the northwestern mediterranean gulf of lions and the subsequent formation of mediterranean deep water were observed using advanced oceanographic instrumentation during a six week long experiment in 1987 the severe 1987 european winter forced an intense outbreak of the mistral a cold dry wind blowing down the rhone valley in mid january surface cooling and evaporation were of sufficient intensity to cause an initial episode of deep convection shortly before the experiment described here began however several more mistral events took place during the experiment during several cruises into the area ctd and absolute horizontal velocity profiles were measured in the mixed area over the rhone fan as well as across the southern front of this region in addition continuous records of shipboard meteorological and oceanographic parameters air temperature surface salinity etc were made an early february mistral apparently did not produce enough surface cooling to

the chemical composition of ree y th u rich accessory minerals in peraluminous granites of the erzgebirge fichtelgebirge region germany part ii xenotime xenotime from a geochemically heterogeneous series of mildly to strongly peraluminous granites of the erzgebirge germany displays extended compositional variability with respect to abundances of hree y u and th with few exceptions the maximum and minimum concentrations for the lanthanides and actinides exceed those noted for this mineral from other geologic environments xenotime chemistry is dominated by the theoretical end members hree po 4 and ypo 4 90 mol in total typical xenotime grains from the erzgebirge granites and from other granites worldwide contain 70 80 mol ypo 4 and 16 25 mol hree po 4 this study documents the occurrence of xenotime abnormally rich in hree in place of y with up to 45 mol hree po 4 substitutions of thorite coffinite th u pb sio 4 brabantite ca th u po 4 2 and monazite la sm po 4 are of minor importance reaching maximum levels of 5 6 mol each with a total contribution typically th u super 4 ca super 2 the total lanthanide and actinide contents in xenotime and host granite are not strongly correlated however formation of xenotime unusually rich in hree occurs only in the a type limica granites that are strongly enriched in these elements the shapes of hree patterns of xenotime and host rock are similar which combined with mass balance calculations indicate the importance of this mineral in affecting the hree as well as y evolution of late stage granitic melts late xenotime may show strong y ho fractionation thus recording the decoupling of y and the hree which can occur in the latest stages of crystallization of evolved granites and which may be associated with deuteric alteration

what induced the exceptional 2005 convection event in the northwestern mediterranean basin answers from a modeling study 1 open sea convection occurring in the northwestern mediterranean basin nwmed is at the origin of the formation of western mediterranean deep water wmdw one of the main mediterranean water masses during winter 2004 2005 a spectacular convection event occurred observed by several experimental oceanographers it was associated with an exceptionally large convection area and unusually warm and salty wmdw explanations were proposed tentatively relating the unusual characteristics of this event to the eastern mediterranean transient emt or to the atmospheric conditions during winter 2004 2005 in the nwmed they could however not be supported until now here we used numerical modeling to understand what drove this convection event the control simulation performed for the period 1961 2006 reproduces correctly the long term evolution of the mediterranean sea circulation the emt and the nwmed convection event of 2004 2005 sensitivity simulations are then performed to assess the respective contributions of atmospheric and oceanic conditions to this event the weakness of the winter buoyancy loss since 1988 in the nwmed prevented strong convection to occur during the 1990s enabling heat and salt contents to increase in this region this resulted in the change of wmdw characteristics observed in 2005 the strong buoyancy loss of winter 2004 2005 was responsible for the intensity of the convection observed this winter in terms of depth and volume of newly formed wmdw the emt did not fundamentally modify the convection process but potentially doubled this volume by inducing a deepening of the heat and salt maximum that weakened the preconvection stratification

the petrology and origin of the tertiary lundy granite bristol channel uk the british tertiary volcanic province btvp comprises within plate central igneous complexes associated with plateau lavas and regional dyke swarms lundy is the southernmost complex of the btvp and comprises granite small tilde90 emplaced into deformed devonian sedimentary rocks within the hercynian cornubian granite province of southwest england the complex is intruded by a northwest southeast trending dyke swarm in common with other btvp igneous complexes lundy is associated with positive gravity and magnetic anomalies which are interpreted in terms of the presena of an underlying basic intrusion at shallow depth with a volume exceeding that of the overlying granite the lundy intrusion is a coarse grained megacrystic granite containing up to 20 alkali feldspar megacrysts in a coarse grained groundmass composed of alkali feldspar quartz lithium bearing muscovite and biotite lithian siderophyllite with a range of aaxssory minerals the main granite has a coarse grained locally miarolitic pegmatitic facies and is intruded by thin sheets and veins of fine grained aplite and microgranite the mineralogy indicates crystallization of the lundy granite from a highly fractionated h2o and halogen rich magma at a relatively shallow crustal level the main lundy granite is a peraluminous leucogranite with na2o 3 4 k2osmall tilde5 low tio2 meo cao zr and sr and high rb and rb sr in comparison with many other peralurninous granites including those from the cornubian batholith and the btvp a new rb sr whole rock isochron for the granite yields an age of 58 7 1 6 ma with an initial 87sr 86sr of 0 715 0 006 nd values for the granite i 0 9 to 1 9 plot between contemporaneous mantle positive nd and cornubian granites nd ca i 11 the trace element data rb y nb show affinities with syn collision and within plate granites as the sr isotope data indicate a major crustal component and the nd isotope data suggest both mantle and crustal components we propose that the lundy granite is derived from a parental magma comprising crustal components derived from a similar source to that of the cornubian granite batholith and a mantle derived component derived from a differentiate of contemporaneous basaltic magma this magma experienced fractional crystallization of plagioclase alkai feldspar fe mg minerals and ree bearing accessory minerals before emplacement and the lundy granite experienced further in situ fractional crystallization associateded with crustal contamination by the devonian shale after emplacement

observations inferences and mechanisms of the atlantic meridional overturning circulation a review this is a review about the atlantic meridional overturning circulation amoc its mean structure temporal variability controlling mechanisms and role in the coupled climate system the amoc plays a central role in climate through its heat and freshwater transports northward ocean heat transport achieved by the amoc is responsible for the relative warmth of the northern hemisphere compared to the southern hemisphere and is thought to play a role in setting the mean position of the intertropical convergence zone north of the equator the amoc is a key means by which heat anomalies are sequestered into the ocean s interior and thus modulates the trajectory of climate change fluctuations in the amoc have been linked to low frequency variability of atlantic sea surface temperatures with a host of implications for climate variability over surrounding landmasses on intra annual timescales variability in amoc is large and primarily reflects the response to local wind forcing meridional coherence of anomalies is limited to that of the wind field on interannual to decadal timescales amoc changes are primarily geostrophic and related to buoyancy anomalies on the western boundary a pacemaker region for decadal amoc changes is located in a western transition zone along the boundary between the subtropical and subpolar gyres decadal amoc anomalies are communicated meridionally from this region amoc observations as well as the expanded ocean observational network provided by the argo array and satellite altimetry are inspiring efforts to develop decadal predictability systems using coupled atmosphere ocean models initialized by ocean data

observations of deep convection in the gulf of lions northern mediterranean during the winter of 1991 92 abstract during december 1991 to april 1992 measurements with moored acoustic doppler current profiler adcp stations and shipboard surveys were carried out in the convection regime of the gulf of lions northwestern mediterranean first significant mixed layer deepening and generation of internal waves in the stratified intermediate layer occurred during a mistral cooling phase in late december mixed layer deepening to about 400 m eroding the salinity maximum layer of saltier and warmer levantine intermediate water and causing temporary surface layer warming followed during a second cooling period of late january during a mistral cooling period from 18 to 23 february 1992 convection to 1500 m depth was observed where the size of the convection regime was 50 100 km extent vertical velocities 40 640 m deep recorded by four adcps of a triangular moored array of 2 km sidelength in the center of the convection regime exceeded 5 cm s 1 and were not correlated over the separation of the moorings hori

on the relationship between the water mass pathways and eddy variability in the western mediterranean sea the role of eddies on the formation and spreading of water masses in the western mediterranean sea is studied with an ocean general circulation model the model is forced with interannually variable surface forcing for the years from 1979 to 1999 it is found that the model reproduces the major features of the observed mesoscale variability in the gulf of lions and the large eddies evolution in the algerian basin the seasonal evolution of circulation in the gulf of lions and processes of spreading of newly formed intermediate deep waters in the postconvection period is studied for years 1987 and 1992 the model results are compared with data from observations it is shown that the instability of the transition zone between old and newly formed deep waters which takes place after the violent mixing stages of the deep convection leads to collapse of the mixed patch and formation of mesoscale eddies some of these eddies propagate out of the gulf of lions transporting deep waters into the algerian basin the rest of the mesoscale eddies filled with newly formed deep waters remain in the gulf of lions and tend to merge and enlarge after the cyclonic eddies reach the algerian basin they interact with the intense mesoscale field existing there the energy analysis shows that the winter and spring are seasons of intensified baroclinic instability of the mean flow in the two regions of interest the gulf of lions and algerian basin the kinetic energy is released by baroclinic instability in spring and summer the spring spectra in the two regions have maximums at horizontal scales of about 80 100 km which is the typical scale of the eddies in the model these eddies propagate a cyclonic circuit the resulting eddy induced mass transport in deep and intermediate layers is directed out of the gulf of lions and toward the gibraltar strait equivalently we can argue the intermediate and deep waters conveyor belt of the western mediterranean sea is eddy drive

fluorine as a tool in the petrogenesis of quartz bearing magmatic associations applications of an improved f oh biotite apatite thermometer grid abstract fluorine contents of whole rock and biotites allow to discriminate quartz bearing magmatic associations through the nature of protoliths and petrogenetic processes f and rb are used to discriminate crustal and mantle derived melts with the exception of calcalkaline association in which mantle contribution may be significant the other quartz bearing associations are essentially derived from crustal melting by biotite and or amphibole vapor absent reactions based on experimental data and on an improved biotite apatite thermometer grid closure temperatures from near liquidus to near solidus conditions as well as fh2o fhf evolution during cooling are determined for the different magmatic associations it appears that the liquidus temperature and fh2o fhf decreases in the order high silica alkaline high k calcalkaline and calcalkaline associations while the solidus temperature follows an inverse order the fh2o fhf values for the peraluminous associations vary over a wide range and overlap the fh2o fhf values of the high k calcalkaline and calcalkaline associations

monitoring open ocean deep convection from space deep convection dc is a key process of the oceanic circulation costly to monitor in situ and under the influence of climate change our study is a first step toward monitoring dc from space we investigate the feasibility of observing its variability using improved satellite altimetry an oceanic simulation of the mediterranean circulation was performed for the 1999 2007 period dc interannual variability is realistically modelled and the sea surface elevation sse is in agreement with altimetry data numerical results show a strong correlation between the annual dc characteristics and the winter sse from that we propose a method to monitor dc interannual variability and long term evolution using altimetry data our method applied to the longest available altimetry series represents correctly the interannual variability of dc in the northwestern mediterranean between 1994 and 2007 citation herrmann m j bouffard and k beranger 2009 monitoring open ocean deep convection from space geophys res lett 36 l03606 doi 10 1029 2008gl036422

the western mediterranean deep water a proxy for climate change reconstructions of mediterranean ocean temperature fields back to 1950 show a proxy relationship between heat content changes in the north atlantic and the western mediterranean deep water wmdw formed in the gulf of lions in winter because of consistent air sea heat fluxes over these areas strongly correlated to the north atlantic oscillation nao

origin and some geomorphological changes of majuli island of the brahmaputra river in assam india abstract the present study on majuli the largest river island of the brahmaputra aims at exploring its origin and geomorphological evolution during the last century according to the earlier official data in 1901 the island covered an area of 1255 km2 the databases of the study comprised historical reports soi topographic maps of 1917 1966 1972 and satellite images of 1996 and 2001 the brahmaputra and one of its major tributaries the dihing once flowed parallel and close to each other an extreme flood which occurred around 1750 appears to have diverted part of the flow of the brahmaputra through the channel of the dihing about 190 km upstream of its confluence when the two rivers joined the intervening land area formed the majuli island according to the first geographical report majuli was a cluster of 15 large and numerous small islands in 1792 the description of the island during the 19th century has been given based on various written reports whereas the changes in the island during 20th century have been assessed in detail at different parts of the island by superimposing the bank lines of 1917 1966 1972 1996 and 2001 and subdividing the island into an array of twenty six 5 latitude 5 longitude blocks the rate of bank line shift has not been uniform throughout the island in time and space migration leading to erosion along the brahmaputra is dominant at the south bank the maximum rate of retreat being 0 480 km year bank line migration leading to silting is confined chiefly to the north bank due to the subansiri river the maximum rate of advance being 0 146 km year in 1917 the island had an area of 751 31 km2 which gradually shrank to 564 01 km2 in 1966 1972 453 76 km2 in 1996 and 421 65 km2 in 2001 similar changes were noticed in the length and width of the island the average annual rate of erosion was 1 77 km2 from 1917 to 1972 1 84 km2 from 1972 to 1996 and 6 42 km2 from 1996 to 2001 indicating a gradual increase in the rate of erosion in later periods in 1917 the number of named streams draining majuli was 49 which decreased to only 7 in 1966 1972 drainage density was 0 963 km km2 in 1917 which decreased to 0 442 km km2 in 1966 1972 similarly stream frequency also decreased from 0 346 km2 in 1917 to 0 144 km2 in 1966 1972 majuli has a fairly large number of swamps and wetlands the larger swamps owe their origin to pre existing rivers the total number of swamps and wetlands observed during 1917 was 112 covering total area of 20 13 km2 which decreased to 50 occupying a composite area of 17 88 km2 during 1966 1972

near surface circulation of the nordic seas as measured by lagrangian drifters in the period june 1991 to august 1993 107 argos tracked drifters drogued to 15 m depth were released in the nordic seas or greenland iceland and norwegian seas the drifter movements revealed the strong and spatially confined current systems along the surface salinity fronts of the iceland faroe frontal zone and of the norwegian coast and along the continental margins and their extensions to the barents sea and spitsbergen the norwegian atlantic current is composed of three distinct streams two continental margin and one coastal branches which join into one single swift mean current west of the lofoten and vesteralen islands where the strongest measured currents are in excess of 110 cm s 1 in addition to the general cyclonic gyre circulation in the nordic seas the drifters indicate smaller cyclonic circulation patterns in all the major subbasins i e the iceland plateau the norwegian the lofoten and the greenland basins no surface signature of the east icelandic current is disclosed by the drifters interpolated and low pass filtered position data were used to construct maps of 15 m depth ensemble mean velocity velocity variability and residence time vigorous eddy fields are dominant in the strong currents and in the lofoten basin eulerian correlations indicate that they tend to propagate to the west in contrast the iceland plateau appears quiescent both in the mean and eddy velocities single particle diffusivities are computed and are found to be in the range 1 7 107 cm2 s 1 the corresponding lagrangian timescale and space scale are 1 3 days and 10 40 km respectively these lagrangian drifter measurements compose the first basin scale accurate near surface velocity data set of the nordic seas

shallow subsurface stratigraphy and alluvial architecture of the kosi and gandak megafans in the himalayan foreland basin india abstract the kosi and the gandak are two major himalayan tributaries of the ganga river in the north bihar plains india with a large hinterland in the nepal himalaya both these rivers have generated megafans in the plains over the quaternary time scale both these rivers are known to be highly dynamic and sediment charged a few conceptual models and limited field data suggested that these megafans have produced thick sand sheets over late quaternary period but these ideas have remained speculative and there is no data on the size and dimension of these sand bodies this paper attempts to reconstruct the subsurface stratigraphy and alluvial architecture for the upper 100 m of the megafans based on electrical resistivity soundings borehole data and drill cores alluvial architecture of the kosi megafan shows significant variability from proximal to medial parts of the fan in terms of sediment grain size and layer thicknesses while the medial part shows 20 30 m thick medium to coarse sand sheets which are laterally stacked the proximal part of the fan has a dominantly gravel unit below 15 m depth that is underlain and overlain by medium to coarse sand units further the medial fan also shows significant vertical and lateral variability in alluvial stratigraphy the near surface

open ocean convection observations theory and models we review what is known about the convective process in the open ocean in which the properties of large volumes of water are changed by intermittent deep reaching convection triggered by winter storms observational laboratory and modeling studies reveal a fascinating and complex interplay of convective and geostrophic scales the large scale circulation of the ocean and the prevailing meteorology two aspects make ocean convection interesting from a theoretical point of view first the timescales of the convective process in the ocean are sufficiently long that it may be modified by the earth s rotation second the convective process is localized in space so that vertical buoyancy transfer by upright convection can give way to slantwise transfer by baroclinic instability moreover the convective and geostrophic scales are not very disparate from one another detailed observations of the process in the labrador greenland and mediterranean seas are described which were made possible by new observing technology when interpreted in terms of underlying dynamics and theory and the context provided by laboratory and numerical experiments of rotating convection great progress in our description and understanding of the processes at work is being made

an extensive western mediterranean deep water renewal between 2004 and 2006 1 the deep waters of the western mediterranean are known to have an almost constant trend towards higher salinity and temperature values since the 1950s recent observations have shown an acceleration of this tendency which has been attributed by some authors to the effect of the propagation of the signal of the eastern mediterranean transient from east to west from 2004 to 2006 five basin scale oceanographic cruises evidenced a relevant change in the deep structure of the western mediterranean in less than two years almost the whole deep basin has been filled with highly saline and warm new deep water which substantially renewed the resident deep water the paper shows evidence of the rapid basin wide extension of the event giving insights into the origin and the propagation of the new deep water towards the basin interior and showing the evolution of the deep characteristics

mediterranean outflow mixing and dynamics the mediterranean sea produces a salty dense outflow that is strongly modified by entrainment as it first begins to descend the continental slope in the eastern gulf of cadiz the current accelerates to 1 3 meters per second which raises the internal froude number above 1 and is intensely turbulent through its full thickness the outflow loses about half of its density anomaly and roughly doubles its volume transport as it entrains less saline north atlantic central water within 100 kilometers downstream the current is turned by the coriolis force until it flows nearly parallel to topography in a damped geostrophic balance the mixed mediterranean outflow continues westward slowly descending the continental slope until it becomes neutrally buoyant in the thermocline where it becomes an important water mass

observations of open ocean deep convection in the northwestern mediterranean sea seasonal and interannual variability of mixing and deep water masses for the 2007 2013 period we present here a unique oceanographic and meteorological data set focus on the deep convection processes our results are essentially based on in situ data mooring research vessel glider and profiling float collected from a multiplatform and integrated monitoring system moose mediterranean ocean observing system on environment which monitored continuously the northwestern mediterranean sea since 2007 and in particular high frequency potential temperature salinity and current measurements from the mooring lion located within the convection region from 2009 to 2013 the mixed layer depth reaches the seabed at a depth of 2330m in february then the violent vertical mixing of the whole water column lasts between 9 and 12 days setting up the characteristics of the newly formed deep water each deep convection winter formed a new warmer and saltier vintage of deep water these sudden inputs of salt and heat in the deep ocean are responsible for trends in salinity 3 3 0 2 10 3 yr and potential temperature 3 2 0 5 10 3 c yr observed from 2009 to 2013 for the 600 2300 m layer for the first time the overlapping of the three phases of deep convection can be observed with secondary vertical mixing events 2 4 days after the beginning of the restratification phase and the restratification spreading phase still active at the beginning of the following deep convection event

overturning the mediterranean thermohaline circulation for more than five decades the mediterranean sea has been identified as a region of so called thermohaline circulation namely of basin scale overturning driven by surface heat and freshwater exchanges the commonly accepted view is that of an interaction of zonal and meridional conveyor belts that sink at intermediate or deep convection sites however the connection between convection and sinking in the overturning circulation remains unclear here we use a multidecadal eddy permitting numerical simulation and glider transport measurements to diagnose the location and physical drivers of this sinking we find that most of the net sinking occurs within 50 km of the boundary away from open sea convection sites vorticity dynamics provides the physical rationale for this sinking near topography only dissipation at the boundary is able to balance the vortex stretching induced by any net sinking which is hence prevented in the open ocean these findings corroborate previous idealized studies and conceptually replace the historical offshore conveyor belts by boundary sinking rings they challenge the respective roles of convection and sinking in shaping the oceanic overturning circulation and confirm the key role of boundary currents in ventilating the interior ocean

modeling the intense 2012 2013 dense water formation event in the northwestern mediterranean sea evaluation with an ensemble simulation approach the northwestern mediterranean sea is a well observed ocean deep convection site winter 2012 2013 was an intense and intensely documented dense water formation dwf event we evaluate this dwf event in an ensemble configuration of the regional ocean model nemomed12 we then assess for the first time the impact of ocean intrinsic variability on dwf with a novel perturbed initial state ensemble method finally we identify the main physical mechanisms driving water mass transformations nemomed12 reproduces accurately the deep convection chronology between late january and march its location off the gulf of lions although with a southward shift and its magnitude it fails to reproduce the western mediterranean deep waters salinification and warming consistently with too strong a surface heat loss the ocean intrinsic variability modulates half of the dwf area especially in the open sea where the bathymetry slope is low it modulates marginally 3 5 the integrated dwf rate but its increase with time suggests its impact could be larger at interannual timescales we conclude that ensemble frameworks are necessary to evaluate accurately numerical simulations of dwf each phase of dwf has distinct diapycnal and thermohaline regimes during preconditioning the mediterranean thermohaline circulation is driven by exchanges with the algerian basin during the intense mixing phase surface heat fluxes trigger deep convection and internal mixing largely determines the resulting deep water properties during restratification lateral exchanges and internal mixing are enhanced finally isopycnal mixing was shown to play a large role in water mass transformations during the preconditioning and restratification phases

age and petrogenesis of the lundy granite paleocene intraplate peraluminous magmatism in the bristol channel uk the lundy granite forms part of the lundy igneous complex which is the southernmost substantive expression of magmatism within both the british cenozoic igneous province and the wider north atlantic igneous province its qz pl kfs bt grt tpz mineralogy and peraluminous character contrast with other british cenozoic igneous province granites farther north but are similar to the granites of the adjacent early permian cornubian batholith we present the results of mapping petrographical and mineral chemical analysis and the first u pb zircon ages for the granite 59 8 0 4 58 4 0 4 ma and cross cutting basic dykes 57 2 0 5 ma which confirm a paleocene age for magmatism zircon inheritance is limited but two cores imply the presence of early palaeozoic igneous rocks in the unexposed basement of sw england the anomalous southerly location of the lundy igneous complex is a consequence of mantle melting arising from the superimposition of localized lithospheric extension related to intraplate strike slip tectonics with the distal ancestral icelandic plume granite generation primarily reflects crustal partial melting during the emplacement of mantle derived melts the change in geochemical character between the lundy granite peraluminous and other british cenozoic igneous province granites metaluminous or subalkaline indicates a fundamental crustal source control between contrasting peri gondwanan and laurentian basement provinces supplementary material sample locations petrographic summaries mineral chemistry data and secondary ionization mass spectrometry u pb analytical data are available at https doi org 10 6084 m9 figshare c 3886783

paired 26al and 10be exposure ages from lundy new evidence for the extent and timing of devensian glaciation in the southern british isles lundy lies in a strategic geographical position for understanding the glacial history of the british isles the island bears evidence of glaciation largely in the form of ice moulded bedrock and glaciallytransported boulders e an unusual occurrence this far south in the british isles irish sea ice penetrated the western bristol channel overriding lundy from the northwest during the last phase of glaciation in this area the results of paired terrestrial cosmogenic nuclide analyses 26al 10be constrain the timing of this extensive glaciation and provide for the first time an age for the exposure of lundy granite following deglaciation the results from nine paired samples yield 26al 10be exposure ages of 31 4e48 8 ka 10be and 31 7e60 0 ka 26al this challenges the view that any glaciation this far south must belong to middle pleistocene glaciations such as the anglian stage c 480e420 ka and a devensian age for the last glaciation is consistent with findings from the isles of scilly further south however the findings suggest early mid devensian marine isotope stage mis 4e3 glaciation of lundy it also implies that the island was exposed or covered for a short time by non erosive cold based ice at the global last glacial maximum lgm during mis 2 26e21 ka the potential exposure of the island throughout mis 2 contrasts with the evidence from the isles of scilly and the celtic sea which were glaciated at the lgm

age dating of individual grains of uraninite in rocks from electron microprobe analyses it is shown that an electron microprobe analysis of the u th and pb content of a single uraninite uo2 grain may be used to calculate the age of formation of that grain this is known as a chemical age examples are shown for a range of natural samples with a wide range of ages comparison with ages derived from isotopic measurements shows the results to be valid approximate formulae which have been proposed for the calculation of the chemical age are not sufficiently reliable especially where the th content is high and for older ages a method for calculating the age by iteration is presented this uses the full and exact formula and is shown to produce a reliable age for the uraninite compared to isotopic measurements the method is particularly useful for samples where the minerals and mineral textures record information on more than one event two examples of samples recording information on dual ages are discussed to show how these ages can be related to events in the formation of the host rocks in one example an alluvial heavy mineral concentrate is shown to contain uraninites from two distinct sources with significantly different ages in the other example two phases of u mineralisation are distinguished in the same rock sample one phase relates to the genesis of the sediments from which the rock was formed the second phase records remobilisation of the u during later tectonic movement

puzzling over the dynamics of the lofoten basin a sub arctic hot spot of ocean variability 1 a sub arctic hot spot of intense synoptic scale variability is observed in the lofoten basin lb of the norwegian sea using ers 1 2 and envisat satellite altimetry measurements we discover a cyclonic propagation of the synoptic scale sea surface height anomalies around the center of the lb surface drifter trajectories do not reveal an associated coherent near surface cyclonic flow suggesting that the propagating signals have a wavelike nature we identify a dipole and a quadrupole wave modes rotating around the center of the lb obtain analytic dispersion relations for these modes and demonstrate that the observed propagation is a manifestation of topographic rossby waves most of the observed waves have a wavelength of about 500 km and phase speeds ranging from 2 to 10 km day we show that these waves are largely responsible for the localization and amplification of sea surface height variability in the center of the lb

role of resolved and parameterized eddies in the labrador sea balance of heat and buoyancy abstractdeep convection in the labrador sea is an important component of the global ocean ventilation the associated loss of heat to the atmosphere from the interior of the sea is thought to be mostly supplied by mesoscale eddies generated either remotely or as a result of convection itself processes that are not resolved by low resolution ocean climate models the authors first employ a high resolution ocean model forced with high resolution 33 km 3 h atmospheric fields to further elaborate on the role of mesoscale eddies in maintaining the balance of heat and buoyancy in the labrador sea in general agreement with previous studies it is found that eddies remove heat along the coast and supply it to the interior some of the eddies that are generated because of the barotropic instability off the west coast of greenland are recaptured by the boundary current in the region of deep convection the convergence of heat and buoyancy by eddies significantly increases with the deepening of the winter

baroclinic instability and the mesoscale eddy field around the lofoten basin the vigorous mesoscale eddy field around the lofoten basin west of northern norway is thought to be related to eddy shedding from the norwegian atlantic current flowing along the norwegian coast here we study baroclinic instability in the current with a particular focus on the influence of topography the flow over the steepest part of the continental slope is found to be the most unstable the growth characteristics cannot be understood from eady theory alone but require the consideration of interior potential vorticity gradients a study of the fully developed macroturbulent field shows that eddy kinetic energy is advected away from the generation regions and that nonlinear effects likely draw the eddy statistics away from the linear growth regime

multiscale observations of deep convection in the northwestern mediterranean sea during winter 2012 2013 using multiple platforms during winter 2012 2013 open ocean deep convection which is a major driver for the thermohaline circulation and ventilation of the ocean occurred in the gulf of lions northwestern mediterranean sea and has been thoroughly documented thanks in particular to the deployment of several gliders argo profiling floats several dedicated ship cruises and a mooring array during a period of about a year thanks to these intense observational efforts we show that deep convection reached the bottom in winter early in february 2013 in a area of maximum 28 3 109 m2 we present new quantitative results with estimates of heat and salt content at the subbasin scale at different time scales on the seasonal scale to a 10 days basis through optimal interpolation techniques and robust estimates of the deep water formation rate of 2 0 0 2 sv we provide an overview of the spatiotemporal coverage that has been reached throughout the seasons this year and we highlight some results based on data analysis and numerical modeling that are presented in this special issue they concern key circulation features for the deep convection and the subsequent bloom such as submesoscale coherent vortices scvs the plumes and symmetric instability at the edge of the deep convection area

radioelement distribution in the tertiary lundy granite bristol channel uk the radioelement distribution and content of the lundy granite a coarse grained megacrystic granite of tertiary age has been measured using a portable gamma ray spectrometer in order to assess fractionation and alteration processes in the granite results indicate a systematic variation of k th and u with a few notable exceptions that follows a partially concentric distribution to lower concentrations inland the plateau region of the island particularly the southern half is relatively depleted in all radioelements over the island measurements of k vary from 1 3 4 9 wt th varies from 5 0 20 3 ppm and u varies from 2 0 12 5 ppm a petrographic electron microprobe and autoradiography examination of the granite indicates that the radioelements mainly reside in discrete major and accessory minerals of which k feldspar k biotite k monazite th xenotime u tungsteniferous columbite u and uraninite u are the most important uraninite is rare being preserved only in fresh samples which come mainly from abandoned quarries mass balance modelling indicates that up to 76 6 of uranium could reside in uraninite and where this has been leached by secondary processes such as hydrothermal alteration or weathering then the present radioelement content no longer reflects the original rock composition fission track evidence is presented to show the pathways along which uranium has been mobilized from or within the granite secondary sites of radioelements include fractures cross cutting all major minerals but especially quartz grain boundaries altered cores of plagioclase feldspar and occasionally yellowy brown mixed chlorite smectite replacement product after biotite biotite itself may exhibit secondary tracks along cleavage traces combined effects of crystal fractionation primary variation and secondary alteration best explain the distribution of radioelements with k controlled by fractionation of the major phases k feldspar and biotite th by fractionation of the accessory mineral monazite xenotime and uraninite and u contents by uraninite and tungsteniferous columbite secondary processes have removed much of the uraninite leaving behind indeterminate fe u material along fractures and residual u and th enrichment within altered major minerals there is some evidence to suggest that late radioelement bearing fluids precipitated monazite and uraniferous zircon along fractures during the waning stages of magmatic activity

impact of the spatial distribution of the atmospheric forcing on water mass formation in the mediterranean sea the impact of the atmospheric forcing on the winter ocean convection in the mediterranean sea was studied with a high resolution ocean general circulation model the major areas of focus are the levantine basin the aegean cretan sea the adriatic sea and the gulf of lion two companion simulations differing by the horizontal resolution of the atmospheric forcing were compared the first simulation med16 era40 was forced by air sea fields from era40 which is the ecmwf reanalysis the second simulation med16 ecmwf was forced by the ecmwf analyzed surface fields that have a horizontal resolution twice as high as those of era40 the analysis of the standard deviations of the atmospheric fields shows that increasing the resolution of the atmospheric forcing leads in all regions to a better channeling of the winds by mountains and to the generation of atmospheric mesoscale patterns comparing the companion ocean simulation results with available observations in the adriatic sea and in the gulf of lion shows that med16 ecmwf is more realistic than med16 era40 in the eastern mediterranean although deep water formation occurs in the two experiments the depth reached by the convection is deeper in med16 ecmwf in the gulf of lion deep water formation occurs only in med16 ecmwf this larger sensitivity of the western mediterranean convection to the forcing resolution is investigated by running a set of sensitivity experiments to analyze the impact of different time space resolutions of the forcing on the intense winter convection event in winter 1998 1999 the sensitivity to the forcing appears to be mainly related to the effect of wind channeling by the land orography which can only be reproduced in atmospheric models of sufficient resolution thus well positioned patterns of enhanced wind stress and ocean surface heat loss are able to maintain a vigorous gyre circulation favoring efficient preconditioning of the area at the beginning of winter and to drive realistic buoyancy loss and mixing responsible for strong convection at the end of winter