evidence of greenland sea water in the iceland basin 1 this study evaluates the presence of intermediate water from the greenland sea in the iceland basin deduced from the observed excess of the tracer sulphur hexafluoride sf6 released in the central greenland sea in 1996 the large tracer release experiment has served a unique opportunity to follow the spread of greenland sea intermediate water to the adjacent basins of the nordic seas and to the areas bordering this region in the present study using data from may june 2001 the released tracer was detected at the sill in the faroe bank channel and at several locations in the iceland basin of the north atlantic just downstream the sill and southeast of iceland the estimated excess of the released tracer at the icelandic slope combined with reported values of the volume flow at this location suggest an annual transport rate of approximately 1 4 kg excess sf6 the results suggest an upper transit time from the central greenland sea to the area southeast of iceland of approximately 4 years

multidecadal variability of potential temperature salinity and transport in the eastern subpolar north atlantic the extended ellett line eel hydrographic section extends from scotland to iceland crossing the rockall trough hatton rockall basin and iceland basin with 61 full depth stations at a horizontal resolution of 10 to 50 km the eel samples the upper limb of the atlantic meridional overturning circulation flowing across the iceland scotland ridge into the nordic seas the rockall trough has been sampled nearly four times per year from 1975 to 1996 and the full section annually since 1996 the eel is an exceptionally long timeseries of deep ocean temperatures and salinities this study extends prior work in the rockall trough and examines for the first time 18 year records in the iceland and hatton rockall basins we quantify errors in the timeseries from two sources observational errors and aliasing the data quality and annual sampling are suitable for observing interannual to decadal variability because the variability exceeds our error estimates the upper waters of all 3 basins are cooler fresher from 1997 to 2001 warmer more saline 2001 to 2006 and cooler fresher from 2006 to 2014 a reference level for geostrophic shear is developed heuristically and by comparison with sea surface altimetry the mean northward transport in the upper waters is 6 7 3 7 sv and there is a 6 1 2 5 sv southward flow below the thermocline although the magnitude of the iceland basin overturning circulation 4 3 1 9 sv is greater than in the rockall trough 3 0 3 7 sv the variability is greater in the rockall trough we discuss the results in the context of our understanding of drivers of variability this article is protected by copyright all rights reserved

chemographic relationships of biotite and cordierite in the mcgerrigle thermal aureole gaspe quebec biotite and cordierite occur in a 1 km wide zone of pelitic hornfelses around the mcgerrigle pluton these phases display systematic changes in xfe that can be attributed to continuous reactions involving chlorite or andalusite in the system kfmash through much of the zone biotite and cordierite were products of the breakdown of chlorite close to the pluton this continuous reaction was terminated by a discontinuous reaction that introduced andalusite pelites which interdigitate with apophyses of the intrusive at the pluton margin contain assemblages that record a continuous reaction between biotite cordierite andalusite muscovite and quartz or alternatively the discontinuous breakdown of muscovite and quartz to k feldspar and andalusite the mole fraction of fe in biotite and cordierite increased significantly with the progress of the first continuous reaction and apparently decreased during the second continuous reaction the kd of fe mg between the minerals decreased and apparently increased respectively during the two reactions biotite cordierite chlorite assemblages are interpreted to have been stable at temperatures between 525 c and 615 c and biotite cordierite andalusite assemblages stable at temperatures between 615 c and 635 c the confining pressure was estimated to have been 2 kbar the results of this study suggest that the kd of fe mg between biotite and cordierite is a function of temperature the fe mg exchange characteristics of the controlling continuous reaction and non ideal mixing of fe and mg

the magnetic fraction a tracer of deep water circulation in the north atlantic abstract we report on a mineral magnetic study of a series of holocene marine sedimentary sequences distributed from northern to southern bjorn and gardar drifts 56 n to 61 n and in the charlie gibbs fracture zone about 53 n all the cores are located at water depths bathed by the iceland scotland overflow water isow a precursor of the north atlantic ocean deep water formed in the nordic seas and flowing into northeast north atlantic after passing over the volcanic sills between iceland and scotland the magnetic fraction is composed of low ti content magnetites with a grain size distribution in the pseudo single domain range these grains originate from a unique source in the north through the erosion by the bottom waters of the icelandic basaltic province the magnetic grain size remains fairly constant in each core but on average progressively fines towards the south and downstream likewise the magnetic concentration and mean magnetic flux decrease towards the south the spatial evolution of the magnetic concentration and of the magnetic grain size suggests a transport of these magnetites by bottom currents associated with the overflow water downstream from the source with progressive deposition of this magnetic fraction along the path of the isow this study provides evidence that characterization of the magnetic parameters of sediments deposited in such an oceanographic context of a unique source upstream and a well defined water mass may be used to detect and trace deep oceanic circulation changes

fluid evolution and its role in the genesis of the granite related madeleine copper deposit gaspe quebec the madeleine copper deposit is hosted by biotite hornfels adjacent to the mcgerrigle granitic complex quebec and consists of stockwork orebodies outwardly zoned from bornite chalcopyrite to chalcopyrite pyrrhotite the mineralization predated the peak of contact metamorphism and is associated with biotite and calc silicate vein and alteration assemblages chlorite muscovite alteration and quartz carbonate veins postdated mineralization vein quartz contains low and high salinity aqueous and co 2 ch 4 aqueous and nonaqueous fluid inclusion types isochore projections suggest that the deposit formed at 400 degrees to 600 degrees c and 1 to 2 kbars low ice melting and eutectic temperatures indicate that some aqueous inclusions have high calcium contents a model has been developed for the fluid evolution in which interaction of high salinity orthomagmatic fluids with organic rich shales produced ch 4 n 2 rich fluids and caused biotite alteration locally the orthomagmatic fluids interacted with calcareous beds releasing co 2 and increasing their calcium content the latter subsequently caused calc silicate alteration chlorite muscovite alteration and quartz carbonate veining were caused by lower salinity fluids derived largely from formational waters outwardly decreasing water rock ratios which produced corresponding decreases in temperature and or cu fe and or increases in a sub h 2 s are invoked to explain the observed zonation in sulfide mineralogy

mean full depth summer circulation and transports at the northern periphery of the atlantic ocean in the 2000s a mean state of the full depth summer circulation in the atlantic ocean in the region in between cape farewell greenland scotland and the greenland scotland ridge gsr is assessed by combining 2002 2008 yearly hydrographic measurements at 59 5 n mean dynamic topography satellite altimetry data and available estimates of the atlantic nordic seas exchange the mean absolute transports by the upper ocean mid depth and deep currents and the meridional overturning circulation moc 16 5 2 2 sv at 0 27 55 at 59 5 n are quantified in the density space inter basin and diapycnal volume fluxes in between the 59 5 n section and the gsr are then estimated from a box model the dominant components of the meridional exchange across 59 5 n are the north atlantic current nac 15 5 0 8 sv 0 27 55 east of the reykjanes ridge the northward irminger current ic 12 0 3 0 sv and southward western boundary current wbc 32 1 5 9 sv in the irminger sea and the deep water export from the northern iceland basin 3 7 0 8 sv 0 27 80 about 60 12 7 1 4 sv of waters carried in the moc upper limb 0 27 55 by the nac ic across 59 5 n 21 1 1 0 sv recirculates westward south of the gsr and feeds the wbc 80 10 2 1 7 sv of the recirculating nac ic derived upper ocean waters gains density of 0 27 55 and contributes to the moc lower limb accordingly the contribution of light to dense water conversion south of the gsr 10 sv to the moc lower limb at 59 5 n is one and a half times larger than the contribution of dense water production in the nordic seas 6 sv

north atlantic nordic seas exchanges abstract the northeastern part of the north atlantic is unique in the sense that it is much warmer in the surface than other ocean areas at similar latitudes the main reason for this is the large northward transport of heat that extends to high latitudes and crosses the greenland scotland ridge to enter the nordic seas and the arctic there the warm atlantic water is converted to colder water masses that return southwards over the ridge partly as surface outflows and partly as overflows through the deep passages across the ridge in this paper the state of knowledge on the exchanges especially across the eastern part of the greenland scotland ridge is reviewed based on results from the ices nansen north atlantic norwegian sea exchanges project from the nordic woce project and from other sources the accumulated evidence allows us to describe the exchanges in fair detail the origins of the waters the patterns of their flow towards and over the ridge and their ultimate fate there is also increasing information on temporal variations of the exchanges although dynamical changes are still not well understood quantitative estimates for the volume transport of most of the overflow branches seem reasonably well established and transport measurements of the atlantic inflows to the nordic seas are approaching acceptable levels of confidence which allows preliminary budgets to be presented the deep overflows are driven by pressure gradients set up by the formation of deep and intermediate water the dominance of deep overflows over surface outflows in the water budget argues that this thermohaline forcing also dominates over direct wind stress and estuarine forcing in driving the atlantic water inflow across the greenland scotland ridge while wind stress seems to influence the characteristics and distribution of the atlantic water north of the ridge

observed and modeled pathways of the iceland scotland overflow water in the eastern north atlantic abstract the spreading of iceland scotland overflow water isow in the eastern north atlantic has largely been studied in an eulerian frame using numerical models or with observations limited to a few locations no study to date has provided a comprehensive description of the isow spreading pathways from both eulerian and lagrangian perspectives in this paper we use a combination of previously unreported current meter data hydrographic data rafos float data and a high resolution 1 12 numerical ocean model to study the spreading pathways of isow from both of these perspectives we identify three isow transport cores in the central iceland basin 59 n with the major core along the eastern boundary of the reykjanes ridge rr and the other two in the basin interior based on trajectories of observed and or numerical floats seeded along 59 n we also describe the isow spreading pathways and quantify their relative importance within 10 years 7 11 of isow from 59 n escapes into the irminger sea via gaps in the rr north of the charlie gibbs fracture zone cgfz the water that moves through these gaps principally originates from the shallower isow layer along the rr eastern boundary 10 13 travels further southward until the cgfz where it crosses westward into the western subpolar gyre 18 21 of isow spreads southward along the eastern flank of the mid atlantic ridge into the western european basin web most of the remaining water stays in the iceland basin over the 10 year period a model based investigation provides a first look at the temporal variability of these isow pathways we find that the fraction of southward water exported into the web is anti correlated with the export through the cgfz a result assumed to reflect these pathways interactions with the north atlantic current in magnitude and or position shift

c o h n salt fluids associated with contact metamorphism mcgerrigle mountains quebec a raman spectroscopic study abstract contact metamorphism and metasomatism of a sequence of cambro ordovician pelitic calcareous and psammitic metasediments in the thermal aureole of the devonian mcgerrigle pluton has resulted in the generation of a wide variety of fluid compositions which can be described by the system c o h n salt microthermometric and raman spectroscopic data on fluid inclusions trapped in quartzsulfide veins adjacent to the intrusive contact indicate that three fluid types existed in the aureole 1 h 2 o 2 h 2 o co 2 and 3 ch 2 n 2 co 2 the aqueous fluids have salinities which range from 0 to 50 eq wt nacl cacl 2 this range in fluid compositions resulted from the progressive devolatilization of a variety of lithologies and the release of waters from the intrusion the range in salinity of the aqueous fluids is attributed to variable contributions of high salinity waters from the intrusions and lower salinity dehydration and formation waters some of the co 2 may be orthomagmatic however most of it probably came from decarbonation of calcareous and possibly carbonaceous lithologies ch 4 and n 2 were generated in pelitic units during thermal metamorphism ch 4 from reactions involving bitumen and graphite and n 2 from nh 2 in silicate minerals and possibly from bitumen the restriction of high mole fractions of ch 4 and n 2 to water free fluid inclusions can be explained by fluid immiscibility within the fracture system the partitioning of co 2 between water poor and water rich fluids was less extreme and in some cases co 2 and h 2 o may have been completely miscible

hydrography and sedimentation under the deep western boundary current on bjorn and gardar drifts iceland basin abstract the interaction of northern component waters overflowing the iceland scotland ridge with sediments further south in the iceland basin has been responsible for highly variable sedimentation patterns since at least the late miocene 5 million years ago and has formed both bjorn and gardar drifts presently this process is maintained by a flux of approximately 3 sv measured along the south icelandic slope of iceland scotland overflow water isow with a mean regional flow direction to the sw which affects sediment transport on bjorn drift below 1350 m depth and over most of the gardar drift coriolis deflection of isow flow causes it to move as a deep western boundary current dwbc in the iceland basin which redistributes sediments under the influence of seabed topography here hydrographic and sedimentological data are used to illustrate the effects and extent of the vigorous dwbc activity the study presents a baseline against which inferred changes in the past can be assessed north of 58 n bottom nepheloid layers with heavy suspended sediment loads are often encountered particularly under the denser and faster flowing core of isow on the eastern slope of gardar drift in this area the presence of migrating regular sedimentary waves is seen on 3 5 khz profiles this is consistent with both the near bottom flow velocity probably in excess of 10 cm s 1 estimated by the geostrophic method and the presence of well sorted foraminiferal sand on the seabed south of 58 n dilute bottom nepheloid layers associated with more tranquil conditions near the seabed inferred from photographic and sedimentological evidence show that currents on gardar drift are weak although most of the south iceland basin is mantled by both regular and irregular non migratory mudwaves the absence of migrating structures with the exception of current intensification associated with discrete basement highs indicates that more sluggish currents characterise this region throughout the region highly variable mean holocene sediment accumulation rates are inferred 2 40 cm ka 1 as a result of the dwbc interacting with the topography

distribution of ammonium in minerals of metamorphic and granitic rocks abstract sixty nine analyses are given for nh4 in minerals of metamorphic and granitic rocks mostly from the ryoke belt japan the distribution of nh4 in coexisting minerals is quite systematic suggesting that nh4 is one of the stable geochemical components in high temperature processes biotite has the highest content of nh4 followed by muscovite k feldspar and plagioclase pure quartz is almost free from nh4 calcic plagioclase contains less nh4 than does sodic plagioclase the partition coefficients d pl bi d kf bi and d kf bi are on the average 0 11 0 38 and 0 43 respectively the fractionation of nh4 in these minerals is quite similar to that of rb but much smaller than that of cs distribution of nh4 as well as those of rb and cs appears to be explained by its ionic radius and the shortest cation o distances in alkali positions of minerals

chronology of greenland scotland ridge overflow what do we really know abstract as a sill constricting the exchange of deep water masses between the nordic seas and the north atlantic which forms an essential part of the atlantic meridional overturning circulation the dynamic height of the greenland scotland ridge and thus its overflow have an important influence on global climate several dsdp odp and iodp sites have been drilled in the north atlantic to shed light on the overflow and climate development reconstructions of bathymetry and sediment thickness have been put forward as well as calculations of the potential temperature of the conduit feeding the iceland plume the available studies have been screened to construct a conceptual model for the evolution of the palaeo circulation in the north atlantic and identify possible weaknesses in our knowledge details e g timing and location about the onset of the overflow are unknown and especially the paleogene development remains enigmatic the database for this period is inadequate and covers only small areas the discussion centres on the earliest traces of the overflow leading to formation of sediment drifts in the eastern north atlantic more data provide a better base to reconstruct variations for the neogene overflow but also appears insufficient for in depth analyses in time and space sediment drifts in the iceland basin indicate a first iceland faroe ridge overflow for the early miocene denmark strait overflow appears to have started in mid miocene times but evidence for this still is sparse grids of high resolution seismic reflection data across all sediment drifts and all limbs of the greenland scotland ridge combined with deeper drill sites targeting the complete sedimentary column down to basement are needed to fully understand the chronology of the greenland scotland ridge overflow and its detailed impact on climate

north atlantic arctic mediterranean exchanges in an ensemble hindcast experiment 1 an ensemble hindcast approach is designed to simulate north atlantic circulation changes during the period 1948 2005 using the max plank institute ocean model forced by atmospheric reanalysis data the experiment seeks to isolate oceanic changes related to the atmospheric forcing history by evaluating the role of initial conditions and masking internal model variability in the ensemble mean results characteristics of the complete north atlantic arctic mediterranean exchange system is described at key sections by time series of exchanges of volume ice heat and liquid freshwater volume transports are divided into water masses by properties and the constructed climatology of exchanges is shown to compare well with available observational estimates of individual branches in response to the atmospheric forcing history we find a modest but robust decline of the atlantic meridional overturning circulation of 0 4 sv decade in total 2 2 5 sv since 1948 in contrast overturning exchanges with the north atlantic and nordic seas and with the nordic seas and arctic ocean show no sign of cessation a marked increase in the freshwater storage of the nordic seas and in particular of the subpolar atlantic accompany the model decline in atlantic overturning the characteristics of the modeled freshening bears similarities with observed patterns of change since the 1950s but whereas the origin of observed freshening is uncertain freshening in the model predominantly results from dynamic changes linked to prominent changes in atmospheric circulation moreover documented increase in the drainage of major arctic rivers is found to have a negligible effect on the oceanic changes

subpolar mode water in the northeastern atlantic 2 origin and transformation 1 the processes that lead to the transformation and origin of the eastern north atlantic subpolar mode waters spmw are investigated from observational data using an extended walin framework air sea flux data from the national oceanography center southampton nocs and hydrographic data from the a24 cruise collected during the world ocean circulation experiment woce are used to estimate the contribution of diapycnal and isopycnal fluxes to the density classes that include spmw surface diapycnal volume flux is the dominant source of waters in the spmw density in the north atlantic subpolar gyre the diapycnal volume flux occurs along the main branches of the north atlantic current nac and it has an average transport of 14 6 5 sv with a maximum of 21 5 sv across the 27 35sq isopycnal the regional distribution of the diapycnal flux on isopycnal surfaces is computed to identify the areas with the largest diapycnal flux these regions coincide with the location of spmw based on potential vorticity the surface diapycnal flux is associated with obduction and subduction through the permanent pycnocline therefore the water involved in the transformation of spmws is continuously exchanged with the ocean interior in addition we suggest that subduction is not associated with smooth advection from the mixed layer to the ocean interior but is water mass loss entrainment into the deep overflows of the subpolar gyre the isopycnal component of the spmw throughput is estimated from the geostrophic transport across the a24 section from greenland to scotland and is 10 to 40 of the diapycnal flux

when do marginal seas and topographic sills modify the ocean density structure 1 we ask what effect marginal seas at high latitudes have on the abyssal densities and stratification of the oceans although marginal seas are not necessary for the formation of dense abyssal waters topographic sills tend to restrict exchange flows and increase density differences laboratory experiments with a steady state large scale overturning circulation forced by a gradient in surface temperatures or heat fluxes show that a marginal sea and topographic sill influence the abyssal density when the sill depth is less than twice the oceanic thermocline depth the overflow over shallow sills interacts directly with the surrounding thermocline stratification decreasing the abyssal density relative to an ocean with no marginal sea and increasing the density difference between the sea and the ocean experiments show that the effect of the sill depends on the surface boundary conditions and indicate a larger response for conditions approaching a prescribed distribution of temperature rather than of heat flux application of the results to the north atlantic circulation suggests that the greenland scotland ridge is shallow enough to lead to a significant reduction of the density of north atlantic deep water and this is consistent with the conclusions from an analysis of water mass properties the greenland scotland ridge is therefore likely to have a significant effect on the density structure and heat transport in the global oceans

intermediate water links to deep western boundary current variability in the subtropical nw atlantic during marine isotope stages 5 and 4 records from ocean drilling program sites 1057 and 1059 2584 m and 2985 m water depth respectively have been used to reconstruct the behavior of the deep western boundary current dwbc on the blake outer ridge bor from 130 to 60 kyr b p marine isotope stage mis 5 and the 5 4 transition site 1057 lies within labrador sea water lsw but close to the present day boundary with lower north atlantic deep water lnadw while site 1059 lies within lnadw high resolution sortable silt mean inline equation grain size and benthic 13c records were obtained and changes in the dwbc intensity and spatial variability were inferred comparisons are made with similar proxy records generated for the holocene from equivalent depth cores on the bor during mis 5e inline equation evidence at site 1057 suggests slower relative flow speeds consistent with a weakening and a possible shoaling of the lsw sourced shallower limb of the dwbc that occupies these depths today in contrast the paleocurrent record from the deeper site suggests that the fast flowing deep core of the dwbc was located close to its modern depth below 3500 m during this interval the benthic 13c suggests little chemical stratification of the water column and the presence of a near uniform lnadw dominated water mass after 111 kyr b p the inline equation record at site 1057 increases to reach values similar to site 1059 for the rest of mis 5 the strengthening of flow speeds at the shallow site may correspond to the initiation of glacial north atlantic intermediate water formation also suggested by a divergence in the benthic 13c records with site 1057 values increasing to 1 2 coupled suborbital oscillations in dwbc flow variability and paleohydrography persisted throughout mis 5 comparison of these data with planktonic 18o records from the sites and alkenone derived sea surface temperature sst estimates from the nearby bermuda rise suggest a hitherto unrecognized degree of linkage between oscillations in subtropical north atlantic sst and dwbc flow

intermediate and deep water paleoceanography of the northern north atlantic over the past 21 000 years benthic foraminiferal stable isotope records from four high resolution sediment cores forming a depth transect between 1237 m and 2303 m on the south iceland rise have been used to reconstruct intermediate and deep water paleoceanographic changes in the northern north atlantic during the last 21 ka spanning termination i and the holocene typically a sampling resolution of 100 years is attained deglacial core chronologies are accurately tied to north greenland ice core project ngrip ice core records through the correlation of tephra layers and changes in the percent abundance of neogloboquadrina pachyderma sinistral with transitions in ngrip the evolution from the glacial mode of circulation to the present regime is punctuated by two periods with low benthic 13c and 18o values which do not lie on glacial or holocene water mass mixing lines these periods correlate with the late younger dryas early holocene 11 5 12 2 ka and heinrich stadial 1 14 7 16 8 ka during which time freshwater input and sea ice formation led to brine rejection both locally and as an overflow exported from the nordic seas into the northern north atlantic as earlier reported by meland et al 2008 the export of brine with low 13c values from the nordic seas complicates traditional interpretations of low 13c values during the deglaciation as incursions of southern sourced water although the spatial extent of this brine is uncertain the records also reveal that the onset of the younger dryas was accompanied by an abrupt and transient 200 300 year duration decrease in the ventilation of the northern north atlantic during the holocene iceland scotland overflow water only reached its modern flow strength and or depth over the south iceland rise by 7 8 ka in parallel with surface ocean reorganizations and a cessation in deglacial meltwater input to the north atlantic

isotopic variations of the fixed nitrogen in metamorphic rocks the content and isotopic composition of fixed nitrogen nh 4 n in metasedimentary rocks phyllites mica schists and gneisses from prograde metamorphic zones in the erzgebirge saxon ore mountains g d r were measured and show that the nitrogen content decreases and 15n increases with increasing metamorphic grade the geochemical and isotopic behaviour of nitrogen during contact metamorphism was investigated in a mica schist profile through the contact aureole of a granitic pluton the nitrogen concentrations of the wall rocks decrease towards the contact whereas the 15n values become higher various model experiments were carried out in the laboratory to explain the changes observed in the rock samples the nitrogen isotope fractionation factor was determined for the isotopic exchange in the system ammonium sulphate ammonia at 250 c 1 0143 0 0012 and 350 c 1 0128 0 0006 in accordance with the model experiments the conclusion seems warranted that the change in nitrogen content and its isotopic composition in rocks during metamorphic processes depend mainly on the metamorphic temperature

overflow waters at the iceland faroe ridge observed in multiyear seaglider surveys abstractthis paper presents new observations of the overflow waters downstream of the faroe bank channel fbc and the iceland faroe ridge ifr between 2006 and 2009 over 17 400 hydrographic profiles were collected during quarterly deployments in the region by autonomous gliders providing previously unrealized spatial resolution to observations downstream of the fbc observations show that the second sill of the fbc coincides with the largest changes in the overflow plume including significant thinning widening and entrainment between the second sill and a topographic feature 75 km downstream the plume bifurcates with the densest portion 65 of the transport descending below 1000 m on the ifr near bottom velocities are directed alongslope with speeds averaging 21 5 cm s 1 observations indicate that 80 of baroclinic velocities associated with mesoscale variability of the overflow plume are smaller than the alongslope topographically induced circulation evidence of overflow is found at all

structure transports and transformations of the water masses in the atlantic subpolar gyre we discuss the distributions and transports of the main water masses in the north atlantic subpolar gyre naspg for the mean of the period 2002 2010 ovide sections 2002 2010 every other year as well as the inter annual variability of the water mass structure from 1997 4x and meteor sections to 2010 the water mass structure of the naspg quantitatively assessed by means of an optimum multiparameter analysis with 14 water masses was combined with the velocity fields resulting from previous studies using inverse models to obtain the water mass volume transports we also evaluate the relative contribution to the atlantic meridional overturning circulation amoc of the main water masses characterizing the naspg identifying the water masses that contribute to the amoc variability the reduction of the magnitude of the upper limb of the amoc between 1997 and the 2000s is associated with the reduction in the northward transport of the central waters this reduction of the northward flow of the amoc is partially compensated by the reduction of the southward flow of the lower limb of the amoc associated with the decrease in the transports of polar intermediate water and subpolar mode water spmw in the irminger basin we also decompose the flow over the reykjanes ridge from the east north atlantic basin to the irminger basin 9 4 4 7 sv into the contributions of the central waters 2 1 1 8 sv labrador sea water lsw 2 4 2 0 sv subarctic intermediate water saiw 4 0 0 5 sv and iceland scotland overflow water isow 0 9 0 9 sv once lsw and isow cross over the reykjanes ridge favoured by the strong mixing around it they leave the irminger basin through the deep to bottom levels the results also give insights into the water mass transformations within the naspg such as the contribution of the central waters and saiw to the formation of the different varieties of spmw due to air sea interaction

isow spreading and mixing as revealed by deep argo floats launched in the charlie gibbs fracture zone to improve our understanding of deep circulation we deployed five deep argo floats 0 4 000 m in the charlie gibbs fracture zone cgfz which channels the flow of iceland scotland overflow water isow a dense water mass of the north atlantic ocean the floats were programed to drift at 2 750 dbar in the isow layer the floats mainly moved westward in the cgfz although some of them followed different routes for few cycles depending on northward intrusions of the north atlantic current over the cgfz one float revealed a direct route for isow from cgfz to the deep western boundary current at flemish cap in the cgfz oxygen data acquired by the floats revealed that the isow layer characterized by salinity higher than 34 94 and density greater than 27 8 kg m was mainly composed of the highly oxygenated isow and the less oxygenated north east atlantic deep water neadw a complex water mass from the east atlantic in the isow layer the relative contribution of isow was generally larger in the northern valley than in the southern valley of cgfz northward intrusions of the north atlantic current above the cgfz increased the relative contribution of neadw in the northern valley and favors mixing between isow and neadw the isow neadw signal flowing westward from the cgfz toward the deep western boundary current was progressively diluted by labrador sea water and denmark strait overflow water oxygen measurements from deep argo floats are essential for a better understanding and characterization of the mixing and spreading of deep water masses

transport of nordic seas overflow water into and within the irminger sea an eddy resolving simulation and observations 1 results from a climatologically forced eddy resolving 1 12 atlantic simulation using the hybrid coordinate ocean model help clarify some presently unresolved connections between volume transports of nordic seas overflow water at key locations in the northernmost north atlantic ocean the model results demonstrate that in addition to the known westward flow through the charlie gibbs fracture zone cgfz some iceland scotland overflow water isow flows westward through gaps in the reykjanes ridge north of the cgfz into the irminger sea and some flows southward along the eastern flank of the mid atlantic ridge into the west european basin these results provide insights into the well known inconsistency between observed westward transport of isow through the cgfz 2 4 sv and the transports upstream at southeast of iceland section 3 2 sv and downstream in the western irminger sea 4 5 sv although the portion of the simulated isow that flows through cgfz is about 500 m deeper than observed the model results also show two isow pathways of this flow into the irminger sea one northward along the western flank of the reykjanes ridge and the other westward before turning north eastward on the western side of the irminger basin comparisons with the long term moored instrument database in the irminger sea show that the model based mean circulation is in reasonable agreement with observed volume transports of overflow water and that it gives approximately correct temperature and salinity characteristics

water masses and circulation pathways through the iceland basin during vivaldi 1996 quasi synoptic data from late 1996 spanning the subpolar north atlantic have been used to determine the major pathways of the north atlantic current nac at that time high spatial resolution allows fronts to be accurately positioned on each seasoar section a clearly defined front of the nac the southern branch turns north at around 25 w and continues through the middle of the iceland basin as far as 60 n 20 w a second branch the northern branch or subarctic front turns north around 30 w and retroflects westward north of 54 n to re enter the irminger basin and become part of the irminger current up the western side of the reykjanes ridge a third eastward branch turns sharply northwest at the mouth of the rockall trough to skirt the southwestern margin of hatton bank this branch carries a tongue of saline eastern north atlantic water enaw over hatton bank and in consequence enaw covers the whole of the hatton and rockall banks as well as the rockall trough bounded in the west by the southern branch the most saline water found in rockall trough spills out into the northern iceland basin between rockall and lousy banks this saline weakly stratified tongue can be traced westward to the south of iceland continuing southwestward along the eastern flank of the reykjanes ridge subarctic intermediate water is carried into the iceland basin creating a fresh tongue bounded east and west by the more saline enaw over hatton bank and the eastern flank of the reykjanes ridge respectively

oceanographic conditions east of iceland circulation and hydrography on the shelf east of iceland and on the western portion of the iceland faeroe ridge is described by a series of surveys using temperature salinity profilers moored current meters and satellite tracked drifters the dominant surface current of the region is the northeastward flow of north atlantic water at the shelf break southeast of iceland as it leaves the shelf to join the iceland faeroe front on the bottom beneath it flowing in the opposite direction is a strong steady current composed of water from the nordic seas that has overflowed the ridge and followed along bathymetric contours north of the front three comparatively weak currents are identified formed by splitting of the north icelandic irminger current after it has rounded the northeast corner of iceland one branch the east icelandic current is confined to the shelf and produces a mean southward flow until it turns eastward to join the iceland faeroe front another leaves the shelf to form the shallow southeastward flowing icelandic current the third follows deeper contours of the continental slope and renews waters on the northern flank of the iceland faeroe ridge

the northern north atlantic ocean mean circulation in the early 21st century the decadal mean circulation in the northern north atlantic was assessed for the early 21st century from repeated ship based measurements along the greenland portugal ovide line from satellite altimetry and from earlier reported transports across 59 5 n and at the greenland scotland sills the remarkable quantitative agreement between all data sets allowed us to draw circulation pathways with a high level of confidence the north atlantic current nac system is composed of three main branches referred to as the northern central and southern branches which were traced from the mid atlantic ridge mar to the irminger sea the greenland scotland ridge and the subtropical gyre at ovide the northern and central branches of the nac fill the whole water column and their top to bottom integrated transports were estimated at 11 0 3 sv and 14 2 6 4 sv 1 sv 106 m3 s 1 respectively those two branches feed the cyclonic circulation in the iceland basin and the flow over the reykjanes ridge into the irminger sea this cross ridge flow was estimated at 11 3 4 2 sv westward north of 58 5 n the southern nac branch is strongly surface intensified and most of its top to bottom integrated transport estimated at 16 6 2 sv is found in the upper layer it is composed of two parts the northern part contributes to the flow over the rockall plateau and through the rockall trough towards the iceland scotland ridge the southern part feeds the anticyclonic circulation towards the subtropical gyre summing over the three nac branches the top to bottom transport of the nac across ovide was estimated at 41 8 3 7 sv because of the surface intensification of the southern nac branch the intermediate water is transported to the northeast atlantic mostly by the northern and central branches of the nac 11 9 1 8 sv eastward this water circulates cyclonically in the iceland basin and anticyclonically in the west european basin with similar transport intensities

differential diagenesis of strontium in archaeological human dental tissues the investigation of prehistoric human migration from the measurement of sr isotope ratios within preserved tissue is critically dependent on the preservation of biogenic sr a number of recent studies have involved isotope ratio measurements on samples of archaeological tooth and bone but doubt remains as to the extent of diagenesis in various skeletal tissues and the effectiveness of procedures designed to decontaminate them the authors have compared sr abundance and isotope ratios in enamel and dentine from archaeological teeth in order to assess the integrity of the biogenic sr signal preserved within the respective tissues it is concluded that enamel appears in most cases to be a reliable reservoir of biogenic sr but that dentine and by implication bone is not the diagenesis of dentine is highly variable even between burials within a single site for the majority of teeth dentine diagenesis was not simply by addition of soil derived sr but involved substantial sometimes complete turnover of the original biogenic material it is suggested that for most of the samples investigated current decontamination techniques may not have been effective in isolating biogenic sr from dentine similar considerations are likely to apply to archaeological and fossil bone but the possibility arises to use dentine and enamel measurements to assess the effectiveness of decontamination procedures which may then be used for bone

graphite ch4 h2o co2 equilibria at low grade metamorphic conditions equilibrium calculations and published phase equilibria are used to show that at temperatures below 400 c and pressures above 300 bar the fluids coexisting with graphite in the c o h system consist either of co2 h2o mixtures or ch4 h2o mixtures bulk fluid compositions consisting of ch4 h2o will unmix to methane rich fluid and h2o rich liquid at temperatures below about 325 c compositions on the co2 h2o join will unmix only at temperatures below about 275 c oxygen fugacity in the ch4 h2o graphite three phase region is fixed at constant p and t and approximately equal to that of the quartz magnetite fayalite assemblage in the co2 h2o graphite three phase region oxygen fugacity is about three orders of magnitude greater from the end stages of diagenesis to temperatures of 300 c and possibly 400 c in salt rich systems many metamorphic rocks may contain ch4 h2o fluids rather than co2 h2o mixtures thus metamorphic reactions involving carbonate minerals would involve ch4 graphite and h2o rather than co2 the immiscibility between ch4 and h2o could result in the common occurrence of methane natural gas in low grade metamorphic terrains

the p v t x f o2 evolution of h2o co2 ch4 bearing fluid in a wolframite vein reconstruction from fluid inclusion studies aqueous carbonaceous and later pure aqueous fluid inclusions in quartz from a ferberite fe 95mn 05 wo4 vein within the low grade metamorphic aureole of the borne granite french massif central have been studied by microthermometry and raman spectrometry the bulk v x properties of the aqueous carbonaceous inclusions have been derived using the equation of state of heyenet al 1982 for the low temperature co2 ch4 system a p t path has been proposed for their trapping using the equations of state of jacobs and kerrick 1981a for the h2o co2 ch4 system two main episodes were reconstructed for the history of the aqueous carbonaceous fluid 1 primary h2o co2 ch4 vapourrich inclusions in quartz indicated the early circulation of a low density fluid 65 mole h2o 34 mole co2 1 mole ch4 and traces of n2 d 0 35 gcm 3 at around 550 50 c and 700 100 bar fluid cooled approximately isobarically to 450 400 c and was progressively diluted by h2o with a concomitant increase in density the fo2 of the h2oco2 ch4 fluid estimated from the equilibrium co2 2h2o ch4 2o2 first ranged from 10 22 to 10 27 bar close to the q f m buffer within analytical errors these values were consistent with the presence of graphite in equilibrium with the fluid 2 a drop in pco2 and therefore a drop in fo2 was recorded by the secondary liquid rich inclusions in quartz the inclusions formed at and below 400 c were composed of h2o and ch4 only and fo2 at that stage was below that fixed by the graphite fluid equilibrium this second episode in the fluid rock system could be explained by the drop of temperature below the blocking temperature of the graphite fluid equilibrium according to this interpretation the blocking of the graphite fluid equilibrium occurred at t 370 c and probably at 400 c on account of the pressure correction mass spectrometric data show that ferberite contains h2o co2 and ch4 in fluid inclusions which lie in the gap of the v x properties of the aqueouscarbonaceous fluid in quartz deposition of ferberite probably occurred at around 400 c the previously inferred blocking temperature resulting from either the drop in pco2 the drop fo2 and or the related ph increase it is concluded that the existence of a blocking temperature for the graphite fluid chemical equilibrium may be a critical factor for maintaining a stable fluid pressure gradient in geothermal systems occurring under greenschist facies conditions in graphite bearing rocks

the flux of dense cold overflow water southeast of iceland abstract from the period commencing midsummer 1990 and lasting for 13 months 13 current meters were deployed on seven moorings at depths between 1000 and 2300 m southeast of iceland 63 09 n 17 18 w to 61 44 n 15 24 w the purpose of the array designated woce acm8 was to measure the overflow of dense water downstream of the source in the faeroe bank channel and downstream of any sources on the iceland faeroe ridge in the depth range 1300 2100 m three of the moorings showed a bottom intensified current that was persistent and directed to the southwest at the other moorings the current was erratic and weak the records were combined to form a transport time series for water denser than 0 27 8 kg m 3 in the direction 240 a mean value of 3 2 0 5 sv was found with considerable variability near a period of seven days but there was no convincing evidence for a seasonal signal the amount of pure norwegian sea water present in the overflow was estimated at 1 6 0 15 sv close to previous determina

hydrography and through flow in the north eastern north atlantic ocean the nansen project abstract the circulation and hydrography of the north eastern north atlantic has been studied with an emphasis on the upper layers and the deep water types which take part in the thermohaline overturning of the oceanic conveyor belt over 900 hydrographic stations were used for this study mainly from the 1987 1991 period the hydrographic properties of subpolar mode water in the upper layer which is transported towards the norwegian sea showed large regional variation the deep water mass was dominated by the cold inflow of deep water from the norwegian sea and by a cyclonic recirculation of lower deep water with a high antarctic bottom water content at intermediate levels the dominating water type was labrador sea water with only minor influence of mediterranean sea water in the permanent pycnocline traces of antarctic intermediate water were found geostrophic transports have been estimated and these agreed in order of magnitude with the local heat budget with current measurements with data from surface drifters and with the observed water mass modification a total of 23 sv of surface water entered the region of which 20 sv originated from the north atlantic current while 3 sv entered via an eastern boundary current of this total 13 sv of surface water left the area across the reykjanes ridge and 7 sv entered the norwegian sea while 3 sv was entrained by the cold overflow across the iceland scotland ridge approximately 1 4 sv of norwegian sea deep water was involved in the overflow into the iceland basin which with about 1 1 sv of entrained water and 1 1 sv recirculating lower deep water formed a deep northern boundary current in the iceland basin at intermediate depths where labrador sea water formed the dominant water type about 2 sv of entrained surface water contributed to a saline water mass which was transported westwards along the south icelandic slope