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

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

asymmetry of free circulations in closed ocean gyres steady flows in regions of closed geostrophic contours such as in ocean basins or over seamounts are examined by calculating solutions to the nonlinear quasigeostrophic and shallow water equations with topography for oceanically realistic choices of parameters the solutions are asymmetric in that those with cyclonic circulation resemble the topography while those with anticyclonic circulation exhibit small scale structure and cross isobath flow these small scale structures reflect topographic wave modes which are stationary with the anticyclonic circulation the implication of the asymmetry is that random wind forcing is much more likely to excite persistent cyclonic than anticyclonic flow this may explain why the circulation in the norwegian and greenland gyres is most often cyclonic

39ar recoil artifacts in chloritized biotite biotite separates from the metamorphosed granitic rocks of eastern taiwan yield disturbed 40ar39ar age spectra their disturbed profiles become more pronounced with increasing degree of chloritization and are attributed to mixed release of argon from sub micron scale biotite and chlorite intercalations 39ar internal recoil best explains the discordance of the age spectra chlorite is randomly intercalated with biotite at scales ranging from 10 a to several tens of microns both 40ar and k were evidently lost during the chloritization reaction during the neutron irradiation 39ar atoms recoil into the chlorite from the adjacent biotite intercalations the recoil and chloritization combine to produce a variable 40ar39ar spatial distribution in the intercalated biotite chlorite during 40ar39ar step heating analyses argon in biotite is released in two pulses centered at 650 c and 950 1050 c which represent two stages of dehydroxylation of the biotite chlorite out gasses in two pulses centered at 550 c and 700 900 c during dehydroxylation and then decomposes this differential thermal release of argon from each mineral phase with variable 40ar39ar ratios yields discordant incremental heating age spectra

rigid topographic control of currents in the nordic seas 1 neutrally buoyant floats deployed across the northern slope of the iceland faroe ridge at 800m depth reveal tight topographic control of their movement a cluster of 22 floats drifts southeast to the faroe shetland channel where it bifurcates such that floats deployed over the upper slope turn south and eventually exit the norwegian sea through the faroe bank channel and floats over the deeper slope turn north in the norwegian sea a subset of the latter group moves quickly north along the western slope of the voring plateau and divides with most of the floats turning east into the lofoten basin and the remainder circulating cyclonically around the norwegian basin this study establishes that i the faroe bank channel overflow waters must come from along the slope north of the faroes not the interior of the norwegian sea and ii exchange of intermediate waters between basins takes place along topographically controlled routes

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

circulation of the chukchi sea shelfbreak and slope from moored timeseries abstract data from a year long mooring array across the shelfbreak upper slope of the chukchi sea are used to describe and quantify the circulation and water masses of the region the timeseries revealed the year round existence of the eastward flowing shelfbreak jet and seaward of this the westward flowing chukchi slope current in the mean the slope current is estimated to transport 0 57 0 04 sv of pacific water while the bottom intensified shelfbreak jet transports 0 009 0 003 sv towards barrow canyon the slope current is surface intensified in summer and fall and in winter and spring it becomes middepth intensified moves shoreward and weakens two extreme states of the circulation were identified 1 an enhanced slope current and reversed westward flowing shelfbreak jet and 2 a strong eastward flowing shelfbreak jet and weak slope current the former state occurs when the wind stress curl on the chukchi shelf is positive and the latter state occurs when the curl is negative a simple theoretical model is used to determine the changes in sea surface height due to such wind stress curl forcing which is consistent with the observed changes in flow seaward of the shelf both in amplitude and phase via geostrophic set up shelfbreak upwelling occurred throughout the year but there was no correlation between the regional wind conditions and the upwelling furthermore there was no apparent relationship between upwelling and the extreme slope current shelfbreak jet events a comparison of water mass signals between the chukchi slope array and a mooring at the head of barrow canyon supports the notion that the slope current is fed by the outflow of pacific water from the canyon

a linear equivalent barotropic model of the antarctic circumpolar current with realistic coastlines and bottom topography abstract a linear equivalent barotropic eb model is applied to study the effects of the bottom topography h and baroclinicity on the total transport and the position of the antarctic circumpolar current acc the model is based on the observation of killworth that the time mean velocity field of the fram model is self similar in the vertical a realistic large scale topography h is constructed by filtering 5 minute resolution data with an appropriate smoothing kernel it is shown that the asymptotic behavior of the solution of the barotropic model a particular case of the eb model in the limit of very small bottom friction depends on subtle details of topography and basin geometry given the uncertainties of the smoothing procedure the authors conclude that the barotropic model is not robust with respect to possible variations of model topography the authors found that the eb model with a vertical profile function similar to that of killworth reproduces the major features of the time and depth ave

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

a numerical investigation of the circulation in the greenland and norwegian seas abstract an ocean general circulation model is used to investigate the circulation in the greenland and norwegian seas the primitive equations are solved on 12 levels with a horizontal grid point distance of 20 km this resolution is sufficient to take into account mesoscale topographic structures which according to observations and the model results presented here have a large influence on the distribution of hydrographic variables however the model is not eddy resolving the baroclinic deformation radius in this region is about 5 km only at first a 2 year experiment is run with the forcing functions and the initial stratification derived from climatological annual mean data compared with quasi synoptic data the calculated temperature and salinity distributions show a much better adjustment to the topography than does the climatology the velocities and transports lie within the range of observed long term mean values the model fields obtained by this experiment are used to initialize another e

an equivalent barotropic mode in the fine resolution antarctic model abstract both the 6 year time mean flow and the eddy kinetic energy in the fine resolution antarctic model are found to be approximately self similar in the vertical with the velocity showing a rapid decay with depth a simple argument is given as to why this would be expected to occur in this and other numerical models and an analysis is given as to the degree of steering of the mean flow by topography

the mean circulation of the southwestern mediterranean sea algerian gyres this is a study about the general circulation of the southwestern mediterranean sea based on observations of currents carried out in the southwestern mediterranean sea in the framework of the mass transfer and ecosystem response mater program eec mast3 program from july 1997 to august 2002 profiling floats medprof experiment isobaric floats liwex experiment and moored current meters elisa experiment give evidence of two large scale barotropic cyclonic circulations the here called western and eastern algerian gyres centered around 3730 n 230 e and 3830 n 600 e respectively these gyres have typical horizontal scales of 100 300 km and are characterized by orbital velocities of about 5 cm s corresponding to rotational periods of about 4 months they are strongly related to the bottom topography of the basin and to the planetary vorticity gradient closed f h isocontours f is the planetary vorticity h the water depth correspond to the locations of the gyres and favor such circulations as free geostrophic modes a linear and barotropic model is used to investigate the possibility of wind driving but the results suggest that the wind stress is not responsible for establishing such circulations the boundary currents flowing along the continental slope of africa sardinia and the balearic islands are proposed to be the main drivers of these gyres

near surface circulation in the northern north atlantic as inferred from lagrangian drifters variability from the mesoscale to interannual 1 the near surface circulation of the nordic seas is basically cyclonic and consists of jets and recirculation cells which are tightly linked to the bottom topography variable forcing by the large scale rotation of the wind leads to a modulation in the strength of the gyres and their interconnecting jets this is seen in drifter and altimeter data currents are stronger during winter and during phases of high north atlantic oscillation index the exchanges between the north atlantic and the nordic seas do not seem to be directly affected by this variable forcing the narrow boundary currents and the intergyre jets are subject to instability causing mesoscale current fluctuations which contribute to the stirring and mixing of polar and atlantic water masses

an empirical evaluation of the argon diffusion geometry in muscovite the temperature time significance of 40ar 39ar muscovite ages is difficult to evaluate quantitatively because of ambiguities in the choice of an appropriate model diffusion geometry the effective diffusion dimension and large uncertainties in experimentally determined diffusion parameters laser 40ar 39ar studies of natural 40ar concentration gradients suggest that argon loss in muscovite occurs primarily via cylindrical volume diffusion commonly with an effective diffusion dimension equal to the crystal diameter the present study tests the cylinder model geometry and the control of physical grain size on the effective diffusion dimension by measuring the anisotropy of a natural40ar diffusion gradient parallel and perpendicular to 001 in a single euhedral muscovite phenocryst the new data combined with previous studies clearly indicate loss of 40ar via cylindrical volume diffusion and strongly suggest that loss of 40ar across the 001 sheets slab diffusion geometry is minimal in undeformed crystals

structure and forcing of observed exchanges across the greenland scotland ridge abstractthe atlantic meridional overturning circulation and associated poleward heat transport are balanced by northern heat loss to the atmosphere and corresponding water mass transformation the

and mg fe si al2 compositional control on argon behaviour in high pressure white micas a continuous laser probe study from the dora maira nappe of the internal western alps italy abstract high pressure white micas from a restricted area in the dora maira nappe of the western alps italy were analyzed by the conventional 40 ar 39 ar bulk sample step heating method and by the step heating and the spot fusion 40 ar 39 ar continuous laser probe techniques on single grains high si ferich phengites from fine grained gneisses display homogeneous 35 40 ma plateau and spot fusion ages consistent with the upper eocene 40 ar 39 ar phengite ages documented over the whole internal western alps in contrast phengite separates and single grains of high si and mg rich to intermediate composition selected from metapelitic and mg rich mica schist samples yield older discordant apparent ages even when sampled in the same outcrop as the fine grained gneisses these local age variations are interpreted to reflect primarily an increasing ar retentivity with increasing mg content in phengites in metapelite derived white micas the isotopic discordance is marked by 1 1 a characteristic bulk sample upward convex spectrum shape 2 2 single grain disturbed age spectra 3 3 a systematic radially outward decrease in spot ages across individual mica cleavage planes and 4 4 strong grain to grain spot age variations in rock sections 1 1 in mg rich mica schists the isotopic discordance is observed as a reproducible upward convex bulk sample age spectrum with high 140 ma intermediate apparent ages 2 2 upward convex single grain age spectra and 3 3 irregular intra and intergrain age gradients on geochemical grounds it is argued that the isotopic discordance occurring in the metapelites is mainly controlled by the compositional changes introduced by the mg fe si al2 celadonitic re equilibration of the high pressure phengites during greenschist overprinting in mg rich phengites this chemical re equilibration may induce ar loss below their presumed higher blocking temperature a model of ar behaviour in high pressure white micas is proposed which explains the age variations recorded throughout the different lithologies in terms of a simple interaction between the mg fe compositional control on ar retentivity and the mg fe si al2 modifications occurring in phengites during progressive overprinting

coherent seasonal acceleration of the weddell sea boundary current system driven by upstream winds abstract the weddell sea is of global importance in the formation of dense bottom waters associated with sea ice formation and ocean ice sheet interaction occurring on the shelf areas in this context the weddell sea boundary current system bcs presents a major conduit for transporting relatively warm water to the weddell sea ice shelves and for exporting some modified form of wedell sea deep and bottom waters into the open ocean this study investigates the downstream evolution of the structure and the seasonality of the bcs along the weddell sea continental slope combining ocean data collected for the past two decades at three study locations the interannual mean geostrophic flow which follows planetary potential vorticity contours shifts from being surface intensified to bottom intensified along stream the shift occurs due to the densification of water masses and the decreasing surface stress that occurs westward towards the antarctic peninsula a coherent along slope seasonal acceleration of the barotropic flow exists with maximum speed in austral autumn and minimum speed in austral summer the barotropic flow significantly contributes to the seasonal variability in bottom velocity along the tip of the antarctic peninsula our analysis suggests that the winds on the eastern north eastern side of the gyre determines the seasonal acceleration of the barotropic flow in turn they might control the export of weddell sea bottom water on seasonal time scales the processes controlling the baroclinic seasonality of the flow need further investigation

a basin coherent mode of sub monthly variability in arctic ocean bottom pressure 1 a sub monthly mode of non tidal variability of ocean bottom pressure obp is observed in a 5 year record of deep sea bottom pressure at the north pole obp records from other regions in the arctic show that the north pole non tidal mass fluctuation is part of a non propagating basin coherent variation that is well represented by the ice ocean model piomas with a basin averaged winter only rms of 3 3 cm wavelet analysis of the modeled obp shows that the basin averaged mass variations are non stationary and only significant during the winter the basin averaged obp is strongly related to the meridional wind component over the nordic seas the ocean response is consistent with episodic wind forcing driving a northward geostrophic slope current the mass transport anomaly associated with the mode is significant relative to the annual net mean flow

on the asymmetry between cyclonic and anticyclonic flow in basins with sloping boundaries the authors present results from laboratory experiments and numerical simulations of the barotropic circulation in a basin with sloping boundaries forced by a surface stress focus is placed on flows with large scale rossby numbers that are significantly smaller than unity the results of the laboratory experiments and simulations show that cyclonic circulation follows the isobaths the flow pattern being independent of the strength of the forcing for anticyclonic circulation the flow pattern changes with forcing strength it is similar to the cyclonic topographically steered pattern for weak forcing and it develops strong cross slope flows for strong forcing linear dynamics are symmetric between cyclonic and anticyclonic circulations and give a good description of the cyclonic and weakly forced anticyclonic circulations the analysis of the nonlinear dynamics shows that topographically steered cyclonic flows are all stable and steady energy minimum solutions to the inviscid nonlinear equations this implies that the nonlinear terms advection of relative vorticity are always small for the topographically steered cyclonic flow for anticyclonic flow the situation is very different it is possible that no anticyclonic topographically steered flow is ever a solution to the steady inviscid equations and if such a steady anticyclonic flow does exist it is likely to be unstable since it must correspond to a saddle point in energy rather than to a minimum or a maximum the nonlinear terms are important when the rossby number is larger than the ekman number which is the case for the anticyclonic experiments with strongest forcing for these experiments the advection of relative vorticity prevents the flow from following topography creating locations with strong relative vorticity and cross slope flow the development of cross slope flow can be understood from the conservation of potential vorticity in basins with irregular topography the separation of anticyclonic flow from steep topography shown in the laboratory experiments and the theoretical analysis herein are in agreement with features like the gulf stream separation from the continental slope at cape hatteras north carolina

the crystal chemical basis for ar retention in micas inferences from interlayer partitioning and implications for geochronology cation partitioning data for coexisting muscovite and biotite are shown to be useful indicators of relative interlayer bond length strength in these minerals these data therefore provide a useful crystal chemical perspective on relative mass transfer kinetics of radiogenic isotopes and account for the observation that biotite is generally less retentive of 40ar and 87sr than coexisting muscovite partitioning behavior of trace elements underscores three reasons why overall interlayer bonding in biotite is weaker than in muscovite first the preferences of large rb cs in biotite and of small la3 and na in muscovite indicate a relatively spacious interlayer volume in biotite suggesting a longer mean k o bond second the preference of interlayer vacancies in biotite with some all possibly h2o h3o filled suggests that its adjacent 2 1 sheets are connected by fewer interlayer bonds per unit cell than those of muscovite third the relative exclusion of large ba2 from biotite despite its large interlayer sites is attributed to o h bonds pointing into the interlayer cavity sub normal to 001 k ba2 h repulsion thereby induced by the bare proton both destabilizes ba2 and weakens k o bonds in contrast muscovite offers a more favorable electrostatic environment for ba2 substitution since its o h bonds are directed into the vacant m1 octahedral site sub parallel to 001 this hypothesis is supported by the observation that progressive f oh 1 exchange enhances ba2 partitioning into biotite phlogopite relative to coexisting muscovite these crystal chemical differences between biotite and muscovite are mirrored in calculated values of ionic porosity z i defined here as the percentage of their interlayer unit cell volume not occupied by ions a monitor of ionic packing density and geometry z i is inversely correlated with k o bond strength which appears to be the rate determining kinetic common denominator for a variety of processes affecting micas including those responsible for loss of radiogenic isotopes in biotite and muscovite accordingly the relatively longer weaker k o bonds of biotite are envisioned as being more easily stretched during volume diffusion or broken during recrystallization or retrograde alteration this in turn accounts for common observations of enhanced radiogenic ar sr loss and younger 40ar 39ar and rb sr ages in natural biotite high z i relative to coexisting muscovite lower z i significantly this pattern may arise irrespective of isotopic loss mechanism diffusion or recrystallization etc and it follows that any age discordance observed between muscovite and biotite cannot be ascribed uniquely to one mechanism or the other without appropriate field petrographic and petrologic constraints extension of this partitioning porosity based synthesis leads to prediction of corollary age retentivity composition effects among chemically diverse trioctahedral and dioctahedral micas which are best field tested in terranes that cooled slowly under dry static conditions pressure effects on argon retention are also inferred from the porosity model

40ar 39ar age gradients in micas from a high temperature low pressure metamorphic terrain evidence for very slow cooling and implications for the interpretation of age spectra estimates of the time temperature history of geologic samples are often based on 40 ar 39 ar ages obtained through incremental heating experiments on minerals with different ar retentivities laser incre mental heating of single crystals of muscovite and biotite from an 1700 ma monzogranite from a low pressure high temperature metamorphic terrain in central arizona suggested an essentially uniform distribution of radiogenic 40 ar in each crystal and yielded ages of 1412 5 ma for the muscovite and 1410 10 ma for the biotite the similarity in these ages implies rapid 25 k m y cooling of the monzogranite after a reheating episode slightly before 1412 ma in contrast detailed age mapping of single crystals from the same samples with the laser microprobe revealed large radiogenic 40 ar gradients indicative of very slow 400 m y evidence for such low cooling rates has important implications for the longevity of high thermal gradients in the early middle proterozoic lithosphere in addition inconsistency between the laser mapping and incremental heating results for these micas suggests caution when interpreting incremental heating data for slowly cooled samples

variability of the norwegian atlantic current and associated eddy field from surface drifters the norwegian atlantic current nwac and its eddy field are examined using data from surface drifters the data set used spans nearly 20 years from june 1991 to december 2009 the results are largely consistent with previous estimates which were based on data from the first decade only with our new data set statistical analysis of the mean fields can be calculated with larger confidence the two branches of the nwac one over the continental slope and a second further offshore are clearly captured the norwegian coastal current is also resolved in addition we observe a semipermanent anticylonic eddy in the lofoten basin a feature seen previously in hydrography and in models the eddy kinetic energy eke is intensified along the path of the nwac with the largest values occurring in the lofoten basin the strongest currents exceeding 100 cm s 1 occur west of lofoten lateral diffusivities were computed in five domains and ranged from 1 5 107 cm2 s 1 the lagrangian integral time and space scales are 1 2 days and 7 23 km respectively the data set allows studies of seasonal and interannual variations as well the strongest seasonal signal is in the nwac itself as the mean flow strengthens by approximately 20 in winter the eke and diffusivities on the other hand do not exhibit consistent seasonality in the sampled regions there are no consistent indications of changes in either the mean or fluctuating surface velocities between the 1990s and 2000s

on the flow of atlantic water and temperature anomalies in the nordic seas toward the arctic ocean the climatic conditions over the arctic ocean are strongly influenced by the inflow of warm atlantic water conveyed by the norwegian atlantic slope current nwasc based on sea surface height ssh data from altimetry we develop a simple dynamical measure of the nwasc transport to diagnose its spatio temporal variability this supports a dynamical division of the nwasc into two flow regimes the svinoy branch svb in the southern norwegian sea and the fram strait branch fsb west of spitsbergen the svb transport is well correlated with the ssh and atmospheric variability within the nordic seas factors that also affect the inflow to the barents sea in contrast the fsb is influenced by regional atmospheric conditions around svalbard and northern barents sea using a composite analysis we further relate anomalous strong svb flow events to temperature fluctuations along the core of atlantic water a warm composite anomaly is found to propagate northward with a tendency to amplify enroute after these events a roughly 12 months delayed temperature signal is identified in the fsb however also in the lofoten basin interior a delayed temperature signal is found which appears to originate from the nwasc this study suggests that hydrographic anomalies both upstream from the north atlantic and locally generated in the norwegian sea are important for the oceanic heat and salt transport that eventually enters into the arctic

an 40 ar 39 ar investigation of the contact effects of a dyke intrusion kapuskasing structural zone ontario an 40ar 39ar study on biotite and hornblende from baked tonalite gneiss adjacent to a 14 m wide kapuskasing dyke in the chapleau block of the kapuskasing structural zone employed resistance furnace step heating of bulk mineral separates single grain laser step heating and laser spot dating of individual grains in thick section all three methods yielded concordant results for the biotite indicating that it has been uniformly overprinted at ca 2 05 ga this date is probably a close estimate of the age of the dyke intrusion the argon data from the hornblende are more difficult to interpret all three methods suggest that the hornblende was partially overprinted and then affected by a later influx of excess argon from the external environment laser spot dates record an apparent age gradient extending radially outward from 2 25 ga in the grain cores to 2 4 2 7 ga in the grain rims corresponding 37ar 39ar values show no systematic variation across the hornblende although 38ar 39ar ratios display a similar pattern to the age distribution with lower values in the cores than in the rims the bulk separate and single grain step heating spectra mimic a volume diffusion ar loss profile that would appear to be inconsistent with the laser spot dates three possible interpretations to explain this apparent discrepancy may involve either experimental difficulties an effective radius of diffusion which is much smaller than the actual grain radius or an effective radius of diffusion that is of the order of the grain radius it is clear that for the 40ar 39ar dating of samples that have experienced complex geologic histories it is important to utilize both resistance furnace and laser techniques

advective and atmospheric forced changes in heat and fresh water content in the norwegian sea 1951 2010 climate variability in the norwegian sea was investigated in terms of ocean heat and fresh water contents of atlantic water above a reference surface using hydrographic data during spring 1951 2010 the main processes acting on this variability were examined and then quantified the area averaged water mass cooled and freshened but a deepening of the reference surface resulted in a positive trend in the heat content of 0 3 w m 2 air sea heat fluxes explained about half of the interannual variability in heat content the effect of the advection of atlantic and arctic waters on the variability varied with time apparently due to large scale changes in the ocean circulation the data are consistent with the explanation that changing wind patterns caused buffering and then release of arctic water in the iceland sea during the late 1960s to early 1970s and this caused large hydrographic changes in the norwegian sea

the effect of the instability of muscovite during in vacuo heating on 40ar 39ar step heating spectra abstract the goal of this study was to ascertain the nature of the ar release mechanism s for a single well characterized muscovite heated incrementally in vacuo 1 at temperatures and time intervals typical of 40ar 39ar step heating experiments and 2 isothermally at 500 c and 700 c for time intervals much longer than typical 40ar 39ar experiments the rate of delamination was monitored by sem and the rate of dehydroxylation was determined by xrd analyses the rate of in vacuo ar loss was compared to that for muscovite heated at 700 c and 2 kbar h2o pressure for all experiments the rate of ar loss was found to be consistent with the rates of dehydroxylation and delamination at 500 c ar loss behavior for a 3000 m diameter muscovite grain was approximated by volume diffusion but the ar release pattern became increasingly non fickian with decreasing grain size we propose that the cause of the non fickian behavior is delamination the portions of the isothermal runs exhibiting diffusion like profiles also yielded discordant 40ar 39ar ages and low atmospheric ar contamination we attribute this phenomenon to the preferential concentration of atmospheric ar in interlayer extended defects and of 40ar in interlayer vacancies whereas 39ar is uniformly distributed throughout the muscovite structure by recoil the 40ar 39ar age spectrum of the muscovite heated under hydrothermal conditions has a staircase shape comparable to that usually interpreted as due to 40ar diffusive loss whereas 40ar 39ar laser spot analyses did not allow this interpretation the in vacuo ar release rate for this sample however indicates that it had been altered during the experiment therefore we propose that this 40ar 39ar age spectrum reflects the differential release of ar from the alteration phases vs muscovite for our sample dehydroxylation and delamination control the in vacuo ar release at temperatures less than 900 c whereas ar diffusion from thin dehydroxylated slabs may dominate the ar release mechanism for temperatures greater than 900 c this model would predict that the recovery of fossil 40ar concentration gradients from muscovite by typical incremental heating schedules is not possible the rates of delamination in vacuo and the rate of ar diffusion for muscovite in nature however both depend upon its the chemical composition structural integrity and grain size consequently for samples with either a naturally occurring broad range of grain sizes such as detrital muscovite and authigenic clay from sedimentary rocks or a compositionally or structurally heterogeneous population of grains such as muscovite from shear zones 40ar 39ar incremental heating may be able to detect intergranular variations in the k ar age

in pursuit of anomalies analyzing the poleward transport of atlantic water with surface drifters we examine the trajectories of 168 drifters as a proxy for atlantic water flowing through the nordic seas the drifters were released at or passed through the svinoy section off the west coast of norway for comparison we generate a set of synthetic trajectories using a stochastic model with a range of diffusivities with the both sets we determine the transit times of both drifters and particles from svinoy to arctic gateways the barents sea and spitsbergen the mean arrival times to these locations are roughly 200 and 500 days respectively this implies ample time for cooling of the surface waters which increases densities and permits subduction before reaching the arctic however a range of transit times is seen some parcels reach fram strait in only 4 months while others are still in the southern nordic seas after 2 years the results do not support the idea that temperature or salinity anomalies can exist as coherent packets the drifters passing svinoy when treated as a group quickly spread over large distances mixing with water in the norwegian and lofoten basins thus an anomaly entering the nordic seas would quickly be obliterated however the velocity of the clusters center of mass is consistent with anomaly propagation speeds inferred previously from hydrographic measurements suggesting the observed variability is advective in nature

simulated low frequency modes of circulation in the arctic ocean the variability of the arctic circulation is investigated for a 43 year period 1951 1993 from a coupled ice ocean model empirical orthogonal function eof analysis shows that the variability of the sea surface height ssh and vertically integrated transport is organized so that in the leading mode the whole arctic operates as a single gyre the mode is associated with the arctic oscillation ao thompson and wallace 1998 and it explains over 70 of the variance in the vertically integrated transport and 25 of the ssh variability the physical interpretation of this mode is derived to arise from its close connection to the atlantic inflow to the arctic the mode shows a major shift toward cyclonic circulation in the end of the 1980s which is associated with a large multiyear pulse of atlantic water to the arctic thus this event appears as the likely initiation of the atlantic layer warming observed during the recent years carmack et al 1995 overall the first mode shows strong decadal variability as reported by proshutinsky and johnson 1997 the second mode of the oceanic circulation which explains 9 of the variance in the transport contains two gyres with opposing cyclonicity in the eurasia and canada basins it projects onto the north atlantic oscillation nao pattern and displays a 14 year cycle which is known to exist in the midlatitude north atlantic surface temperatures deser and blackmon 1993 a further examination reveals that this mode describes the variability of the flow through the barents sea which is modulated by the water mass modification due to the local heat flux variability the apparent nao connection is provided by a simultaneous correlation between the time series of this second mode and the leading heat flux mode in the north atlantic which is associated with nao

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

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

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

nonlinear seismic response of soft clay sites a nonlinear stress strain model utilizing ramberg osgood idealization of backbone curve and allowing for its progressive degradation due to cyclic loading is used to conduct site response studies at two soft clay sites the sites selected are 1 southern pacific building san francisco and 2 station no 119 site tokyo japan the subsurface conditions and the material properties used in analyses are presented the computer program dcharm used for nonlinear analysis allows for progressive degradation of the backbone curve for comparison the results obtained from program shake using equivalent linear idealization are also presented the program dcharm is shown to provide ground response results closer to the recorded data than shake the results obtained indicate that substantially higher accelerations and durations of earthquakes are needed to cause significant degradation of soft clay

seasonal variability of sea surface height in the coastal waters and deep basins of the nordic seas sea surface height measured by the envisat radar altimeter over open ocean and from leads in sea ice are combined to generate a complete view of variability in the nordic seas geographically and seasonally the observed seasonal variability is decomposed using empirical orthogonal functions and is consistent with seasonal variations in steric and dynamic forcing wintertime increase in sea surface height on the east greenland shelf is hypothesised to be caused by wind forced downwelling which provides direct evidence for the regional play of coastal dynamics high levels of eddy kinetic energy around the sea ice edge in fram strait and off east greenland and svalbard are consistent with the interaction of the wind with the ice edge

argon retentivity of hornblendes a field experiment in a slowly cooled metamorphic terrane hornblende from samples of amphibolite and granitic gneiss collected within a single outcrop in the central adirondacks yield significantly different sup 40 ar sup 39 ark sub k dates of 948 plus minus 5 and 907 plus minus 5 ma assuming that this terrane cooled slowly following high grade metamorphism and that the samples have experienced the same thermal history the difference in dates apparently reflects a corresponding difference in blocking temperature for diffusion of radiogenic argon in these hornblende samples the fe fe mg mn of the hornblende samples are 0 8 and 0 6 the higher ratio corresponding to the younger sup 40 ar sup 39 ar sub k date transmission electron microscopy observations indicate that both hornblende samples are homogeneous and devoid of any exsolution but contain zones of fibrous phyllosilicates approximately 0 1 to 2 mu m wide parallelling 100 and 110 these alteration zones probably formed during post metamorphic cooling as a result of the migration of fluids through the hornblendes and are obvious pathways for argon escape from hornblende as these features are more abundant in the hornblende sample with the younger sup 40 ar sup 39 ar date and higher fe fe mg mn they may influence the argon blocking temperature by effectively partitioning the hornblende grains intomore diffusion domains of varying size biotite from the granitic gneiss yields an sup 40 ar sup 39 ar sub k date of 853 plus minus 2 ma with a mildly discordant step heating spectrum that in part reflects the degassing of submicroscopic inclusions precipitated during alteration of the host biotite plagioclase from the amphibolite yields a sup 40 ar sup 39 ar sub k integrated date of 734 plus minus 3 ma less

topographic influence on baroclinic instability and the mesoscale eddy field in the northern north atlantic ocean and the nordic seas abstracta weak planetary vorticity gradient and weak density stratification in the northern north atlantic and nordic seas lead to time mean currents that are strongly guided by bottom topography

representing topographic stress for large scale ocean models abstract interaction of eddies with seafloor topography can exert enormous systematic forces on the ocean circulation this interaction has been considered previously under idealized circumstances theoretical results are here simplified and extended toward practical application in large scale ocean circulation models among the suggestions is that coarse resolution models can correct a depth independent part of the velocity field toward a velocity given by z flh where z is the vertical unit vector f is coriolis form l is a length scale o 10 km and h is the total depth absence of this tendency may be implicated in a number of systematic defects that appear in present ocean models

structure and transports of the east greenland current at 75 n from moored current meters the east greenland current runs from 80 n to 60 n from the fram strait to the denmark strait via the nordic seas it transports waters from the arctic and the nordic seas into the atlantic and also acts as a western intensified southward return flow for waters recirculating within the greenland sea gyre itself an area important for deep water formation data from current meters moored across the current at 75 n in 1994 1995 show a large seasonal variation in the current the annual mean transport is 21 3 sv taking 9 w as the eastern boundary varying from 11 sv in summer to 37 sv in winter errors approximately 5 sv no significant seasonal signal has been observed in the fram or denmark straits suggesting that the seasonal transport is confined within the greenland sea using temperature and velocity data we split the flow at 75 n into two parts a mainly wind driven circulation annual mean of order 19 sv which is trapped within the greenland sea gyre and exhibits a large seasonal cycle transporting predominantly the waters of the greenland sea and a steadier throughflow probably thermohaline driven of order 8 sv in the annual mean with very little seasonal variation data from previous years 1987 1994 indicate the interannual variability of the current is low assuming a spatially coherent structure to the current we extend the time series of the transport back to 1991 and suggest it may be possible to monitor the total transport with one suitably placed mooring

interannual variability in the hydrography of the norwegian atlantic current frontal versus advective response to atmospheric forcing 1 the warm and saline inflow of the north atlantic current to the nordic seas is highly relevant for the region and the global climate north of the greenland scotland ridge the norwegian atlantic current consists of two 40 60 km wide branches situated at the slope and 150 200 km offshore respectively to interpret changes in these branches in terms of climate variability in the northern north atlantic it is important to understand their spatiotemporal response to both atmospheric forcing and advection we analyzed three decades of synoptic hydrographic observations of the branches variability with particular focus on the response to the north atlantic oscillation nao and related wind stress curl changes in the nordic seas to do so we separated the effect of fluctuating position and thickness of the branches from the variability in temperature and salinity in the spatially fluctuating cores as a rapid response to the nao we find a deflection of both branches toward the coast which is consistent with an enhanced basin wide cyclonic circulation while the immediate correlation between hydrographic properties and the nao is weak we find a significant negative correlation when the nao leads temperature and salinity by 4 6 years we attribute the overall delayed response to the advection of anomalies generated in the northwestern north atlantic through nao induced air sea interaction and changes in the position of the subpolar front

an ocean model for climate variability studies abstract models of the time dependent ocean circulation can be simplified considerably by filtering out all short term small scale motions which are unimportant for climatic processes for time scales large compared with a day and space scales large compared with the internal rossby radius of deformation 50 km the currents in most of the interior ocean can be determined diagnostically as quasi equilibrium fields so that only the salinity and temperature fields need be treated prognostically regions of closed f h contours however represent exceptions here trapped vorticity gyres exist as free flow solutions without external forcing and in the presence of forcing the barotropic velocity field must therefore be determined prognostically through a potential vorticity equation for the gyres lateral boundary layers and the equatorial regions also require separate treatment these were not considered specifically but it is suggested that integrated parametrical models analogous in structure to mixed layer models or the integrated boundary layer models of aerodynamics may be the most appropriate technique for coupling these regions to the interior ocean in a comprehensive ocean model suitable for climate studies a coupled multi region model of the global ocean circulation based on these scale considerations could be sufficiently cost effective to permit systematic investigation of the role of the oceanic heat storage and transport in climate variability studies over a wide spectrum of space and time scales the analysis of the seasonal variations of the interior ocean circulation represents a simple example in which the filtered model yields considerably simpler and more readily interpretable results than a fully three dimensional unfiltered model

on the dynamics of the zapiola anticyclone recent observations obtained in the south atlantic suggest the existence of a strong anticyclonic flow positioned over a major bottom topographic feature known as the zapiola drift here a numerical simulation of the south atlantic is described in which this anticyclone is reproduced and the model is used to diagnose the dynamics maintaining this flow with a mean barotropic transport of 140 sv and bottom velocities of 10 cm s 1 the simulated zapiola anticyclone compares well with in situ observations furthermore the model surface eddy kinetic energy shows a local minimum over the drift in agreement with observations from topex poseidon numerical experiments show that the circulation feature is sensitive to the intensity of the eddy field and to the particular value of the bottom friction both of these tendencies are in agreement with a theoretical explanation of the zapiola anticyclone that has recently appeared elsewhere thus we argue that the anticyclone is maintained by eddy driven potential vorticity fluxes accelerating flow within topographically closed ambient potential vorticity contours as far as we know this is the first south atlantic simulation to reproduce the zapiola anticyclone in a realistic fashion the quantitative success of this experiment is attributed to the use of a topography following sigma coordinate in a spatially well resolved model

interpretations of the jebar term abstract in diagnostic calculations of the ocean s circulation the so called jebar joint effect of baroclinicity and relief term may induce a significant depth average current field as has been noted in the oceanographic literature here we present two consistent interpretations of this term in the equation governing the vorticity of the depth averaged current a topographic vortex stretching term proportional to the dot product of depth averaged velocity and the depth gradient arises we show that jebar corrects this term by removing the contribution of the geostrophic flow referenced to the bottom which cannot generate topographic vortex stretching in the evolution equation for the vorticity of the depth integrated flow a bottom torque term is present we show that the jfbar term discussed above enters here as a contribution to the bottom torque emphasizing the role of jebar as a forcing term we also show that when a diagnostic calculation is formulated completely in terms of the transport str

wind feedback mediated by sea ice in the nordic seas air sea interactions play a critical role in the climate system this study investigates wind induced changes in the ocean surface temperature and sea ice cover feeding back onto the atmospheric circulation this interaction was modeled in the nordic seas using a partial coupling method to constrain the ocean with prescribed wind forcing in an otherwise fully coupled earth system model this enabled the evaluation of not only the direct oceanic but also the indirect atmospheric response to idealized forcing scenarios of perturbed winds over the nordic seas the results show that an anticyclonic wind anomaly forcing leads to significant surface cooling in the greenland sea mostly due to anomalous drift of sea ice during winter the cooling reduces the net surface heat flux to the atmosphere and increases sea level pressure the pressure gradients result in anomalous geostrophic southerly winds which locally are comparable both in direction and in velocity to the prescribed forcing anomalies suggesting a positive feedback

some observations on the interpretation of 40ar 39ar age spectra several recent applications of the 40ar 39ar age spectrum technique have utilized the ability of this technique to resolve the internal ar isotope distribution in crystals for the purpose of placing constraints on the timing of thermal events additionally a few of these studies have attempted to use certain properties of the age spectrum to estimate the temperature and duration of heating experienced by the sample during the disturbance although these successful applications are encouraging the interpretation of age spectra of disturbed samples is in many ways still an art form with the beholder apparently relatively free of constraints that might limit an assessment in fact there are a number of restrictions on interpretation imposed by 1 multiple episodic loss 2 slow cooling 3 mixed phases 4 resolution of the age spectrum 5 excess 40ar 6 recoil artifacts 7 grain distribution and size and 8 phase changes while in the vacuum extraction system these effects are discussed with a view to understanding possible ambiguities in ar release patterns in most cases only with independent geochronological knowledge an understanding of the release systematics and complete sample characterization can these constraints be successfully dealt with in a quantitative framework

apparent argon diffusive loss 40ar 39ar age spectra in amphiboles detailed investigations have been made of two amphibole samples where 40ar 39ar age spectra have been interpreted to show argon diffusive loss both samples display complex compositional zoning that reflects partial major and minor element chemical re equilibration during later thermal events that is associated with the loss of radiogenic 40ar the apparent diffusive loss age spectra in these samples are an artefact of this chemical re equilibration process one sample additionally shows the effect of potassium gain and contamination with a potassium rich phase biotite the resulting ages in this sample are geologically meaningless and the apparent fit to a theoretical diffusive loss curve is coincidental this study shows that volume diffusive loss of argon appears to operate at slower rates than argon loss by chemical re equilibration in amphiboles

wind driven variability of the large scale recirculating flow in the nordic seas and arctic ocean the varying depth integrated currents in the nordic seas and arctic ocean are modeled using an integral equation derived from the shallow water equations this equation assumes that mass divergence in the surface ekman layer is balanced by convergence in the bottom ekman layer the primary flow component follows contours of f h the model employs observed winds and realistic bottom topography and has one free parameter the coefficient of the linear bottom drag the data used for comparison are derived from in situ current meters satellite altimetry and a primitive equation model the current meter data come from a 4 yr record at 75 8 ni n the greenland sea the currents here are primarily barotropic and the model does well at simulating the variability the best bottom friction parameter corresponds to a spindown time of 30 60 days a further comparison with bottom currents from a mooring on the norwegian continental slope deployed over one winter period also shows reasonable correspondence the principal empirical orthogonal function obtained from satellite altimetry data in the nordic seas has a spatial structure that closely resembles f h a direct comparison of this mode s fluctuations with those predicted by the theoretical model yields linear correlation coefficients in the range 0 75 0 85 the primitive equation model is a coupled ocean ice version of the princeton ocean model for the north atlantic and arctic monthly mean depth averaged velocities are calculated from a 42 yr integration and then compared with velocities predicted from an idealized model driven by the same reanalyzed atmospheric winds in the largely ice free norwegian sea the coherences between the primitive equation and idealized model velocities are as high as 0 9 on timescales of a few months to a few years they are lower in the remaining partially or fully ice covered basins of the greenland sea and the arctic ocean presumably because ice alters the momentum transferred to the ocean by the wind the coherence in the canadian basin of the arctic can be increased substantially by forcing the idealized model with ice velocities rather than the wind estimates of the depth integrated vorticity budget in the primitive equation model suggest that bottom friction is important but that lateral diffusion is of equal or greater importance in compensating surface ekman pumping

topographic effects on current variability in the caspian sea 1 satellite derived surface height fields reveal that variability in the central and southern basins of the caspian sea is correlated with topography consistently empirical orthogonal functions from current meter data from the southern basin are aligned with the isobaths in addition the gravest mode which accounts for over 80 of the variance has an equivalent barotropic structure in the vertical to what extent this variability can be modeled using a linear analytical model is examined the latter assumes equivalent barotropic flow aligned with the geostrophic contours which in turn are dominated by the topography with ecmwf winds and etopo2 topography the model yields surface height deviations which are significantly correlated with satellite derived estimates on seasonal and longer time scales in the central basin the model is somewhat less successful in the southern basin where the stratification is stronger nevertheless the results are encouraging given the extreme simplicity of the model

observations of the ocean response to cold air outbreaks and polar lows over the nordic seas 1 the impact of intense atmospheric mesocyclones polar lows on the ocean circulation at high latitudes as well as the role of ocean feedbacks on the evolution of these atmospheric systems themselves is under debate here the upper ocean response to atmospheric forcing before during and after polar lows events over the nordic seas is studied a set of 96 unique polar low tracks from 2002 to 2010 are collocated with satellite based sea surface temperature and altimeter observations and with surface drifter observations the satellite data show systematic temperature and sea level drops and enhanced geostrophic kinetic energies over the days leading up to polar low events these data however reveal little information about the ocean response to the polar lows themselves the drifter observations largely agree with the satellite data on the response to synoptic conditions but they also give indication of enhanced upper ocean kinetic energies immediately following the passage of polar lows

ocean change around greenland under a warming climate the impact of climate warming on the ocean near greenland is investigated with a high resolution coupled global climate model the ocean around greenland exhibits a strong warming in response to a four times increase of present day atmospheric co 2 levels the signal is intensified in the intermediate layer and regionally strongest in the greenland sea the projected changes in temperature are driven by changes affecting the large scale ocean circulation rather than changes of the local atmospheric heat forcing the ocean conditions examined here provide a background for the water masses in contact with the outlet glaciers around the greenland coast the future warming of the warm subtropical origin layer could thus lead to enhanced ice sheet melting although the signal could be mitigated by other effects including an enhanced stratification of the surface fresh layer applying a simple parameterization to estimate the change in melt rate along the greenland coast we find that ice sheet melting increases everywhere in response to the change in water mass properties although the melt rate changes show large variations in space the largest melting acceleration is found on the east coast between fram strait and denmark strait where both the parameterization applied to present day conditions and observations suggest moderate melting up to now these model results caution that the greenland ice sheet mass balance should be monitored everywhere and not only where melting occurs at the moment

generation and stability of a quasi permanent vortex in the lofoten basin abstract in the nordic seas the lofoten basin is a region of high mesoscale activity the generation mechanism and the conditions for the stability of a quasi permanent vortex in the center of the lofoten basin are studied with a high resolution ocean circulation model and altimeter data the vortex and its generation mechanism manifest themselves by a pronounced sea surface height ssh signature and variability which are found to be in agreement with altimeter data the vortex results primarily from anticyclonic eddies shed from the eastern branch of the norwegian atlantic current which propagate southwestward the large scale bottom depression of the lofoten basin plays a crucial role for attracting anticyclones into the trough and for enabling the dynamical stability of the vortex the water mass characteristics of the anticyclone lead to enhanced atmospheric interaction heat loss during wintertime the cold water trapped in the upper part of the vortex preconditions convection in the following wi

vertical structure and seasonal variability of the inflow to the lofoten basin inferred from high resolution lagrangian simulations the lofoten basin in the eastern nordic seas plays a central role in modifying the warm atlantic water inflow toward the arctic ocean here the atlantic water experiences increased residence times

a diagnostic model of the nordic seas and arctic ocean circulation quantifying the effects of a variable bottom density along a sloping topography abstract a linear diagnostic model solving for the time mean large scale circulation in the nordic seas and arctic ocean is presented solutions on depth contours that close within the nordic seas and arctic ocean are found from vorticity balances integrated over the areas enclosed by the contours climatological data for wind stress and hydrography are used as input to the model and the bottom geostrophic flow is assumed to follow depth contours comparison against velocity observations shows that the simplified dynamics in the model capture many aspects of the large scale circulation special attention is given to the dynamical effects of an along isobath varying bottom density which leads to a transformation between barotropic and baroclinic transport along the continental slope enclosing both the nordic seas and arctic ocean the along slope barotropic transport has a maximum in the nordic seas and a minimum in the canadian basin with a difference of 9 sv 1 sv 106 m3 s 1 between the two thi

the prevalence of oceanic surface modes satellite observations have revolutionized oceanography capturing diverse phenomena over much of the globe however it remains to understand how surface fields like sea surface height reflect the motion occurring at depth the vertical structure of ocean eddies is often expressed in terms of baroclinic modes which are basis functions derived assuming a flat ocean bottom bathymetry alters the modes though weakening the bottom velocities using analytical solutions we demonstrate that with realistic bathymetry and or bottom friction the bottom velocities are nearly zero the resulting surface modes should be ubiquitous in the ocean this would explain the dominant mode of variability obtained from globally distributed current meter data and is consistent with energy spectra derived from sea surface height data the results yield a simple way to infer subsurface velocities from satellite data and suggest that ocean analyses should be made in terms of surface modes and topographic waves