on the origin of the warm inflow to the nordic seas abstract warm and saline waters enter the nordic seas from the south as part of the warm to cold water transformation of the thermohaline circulation of the northern north atlantic one explanation for the origin of the nordic seas inflow is a shallow source hypothesis under which the inflow waters are a modification of upper ocean subtropical waters warm waters from the subtropical gyre are carried to the eastern north atlantic by the north atlantic current and branch northwards joined by poleward upper thermocline flow along the upper continental slope to provide the nordic seas inflow along this pathway the upper water column is progressively cooled and freshened by winter convection the subpolar mode water transformation process and this sets the inflow characteristics a deep source hypothesis provides an alternative explanation for the characteristics of the nordic seas inflow and the pathway delivering the waters to the inflow under this hypothesis inflow waters originate from the core of the mediterranean overflow waters in the gulf of cadiz carried northward at mid depth by the eastern boundary undercurrent in the subtropics continuing into the subpolar gyre along the eastern boundary and rising from depths near 1200m in the rockall trough to less than 600m to cross the wyville thomson ridge into the faroe shetland channel and thence to the nordic seas the deep source hypothesis focus is on lower thermocline source waters beneath the sill depth for the nordic seas inflow in contrast to the shallow source hypothesis focus of transformation of upper thermocline waters above the sill depth on the basis of regional water mass distributions geostrophic shear and direct current measurements we reject the deep source hypothesis in favor of the shallow source hypothesis rather than a flow of deep mediterranean overflow water along the eastern boundary rising from depth to feed the nordic seas the inflow is supplied directly by transformed north atlantic current waters from the same depth range as the inflow mediterranean overflow water is a constituent of the inflow but only through its contribution to defining the temperature salinity relationship of the interior of the subtropical gyre from which the north atlantic current draws its water rather than by direct northward advection of mediterranean outflow water via the eastern boundary undercurrent crossing from the subtropics into the subpolar domain instead the eastern boundary undercurrent wholly expels its transport of mediterranean overflow water into the eastern edge of the subtropical gyre creating the mid depth westward extending subtropical salinity plume for the lower thermocline isopycnal range of the core of the mediterranean overflow water measurements show that at the wyville thomson ridge the flow is southward and descending rather than northward and rising representing cold spillover from the faroese channels entraining warm upper ocean waters as the spillover plume descends and warms into the northern rockall trough no evidence is found in rockall trough northward of 54 n porcupine bank for direct advection of mediterranean overflow waters via an eastern boundary undercurrent extension and the very dilute mediterranean overflow waters in the trough reflect the interaction of the wyville thomson ridge plume descending into the trough from the north and lower thermocline waters delivered to the trough from the south

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

a numerical study of interannual variability in the north icelandic irminger current author posting american geophysical union 2018 this article is posted here by permission of american geophysical union for personal use not for redistribution the definitive version was published in journal of geophysical research oceans 123 12 2018 8994 9009 doi 10 1029 2018jc013800

eddies in the labrador sea as observed by profiling rafos floats and remote sensing abstract data from profiling rafos floats topex poseidon altimetry and the alongtrack scanning radiometer atsr aboard ers 1 have been used to describe the spatial and seasonal patterns of eddy variability in the labrador sea peaks in sea surface height ssh variability appear in two regions off the west greenland shelf near 61 5 n 52 w where the 3000 m isobath separates from the shelf and in the center of the basin at 58 n 52 w both locations show seasonal ranges in ssh variability of up to 40 mm with the greenland site having largest variability in january march leading the central site by 50 days a sea surface temperature image from the atsr at the greenland site shows numerous eddies both cyclonic and anticyclonic being formed by injection of west greenland current water into the labrador sea interior data from profiling rafos floats launched in 1997 as part of the labrador sea deep convection experiment are used to describe three of the west greenland current eddies in detail one of

an updated view on water masses on the pan west greenland continental shelf and their link to proglacial fjords the accelerated melt of the greenland ice sheet has been linked to a sudden increase in the presence of warm subsurface coastal water in west greenland yet pathways of warm coastal water along the entire west greenland coast have remained largely unstudied here we present the first near synoptic hydrographic observations at both the continental slope and fjord entrances of the west greenland coastal system from cape farewell 59 n to melville bay 75 n in summer 2016 we observed a distinct north south division in the water mass distribution in west greenland approximately partitioned by the northern part of davis strait and a division between the continental slope and fjord entrances waters from the regional southern freshwater source with origin in the east greenland current that rounds cape farewell are not observed to enter baffin bay the regional heat source transported by the west greenland current is blocked by southwest greenland coastal water in the south but the deep connections in the north allow warm deep subpolar mode water to enter fjords furthermore we observed cold and relative saline baffin bay polar water over the inner part of the banks periodically reaching as far south as 64 n suggesting the presence of an undescribed southward current at the southwest greenland continental shelf

deep seismic reflection images of the wharton basin oceanic crust and uppermost mantle offshore northern sumatra relation with active and past deformation 1 we present deep seismic reflection images along two profiles collected in 2006 in the wharton basin offshore northern sumatra the main profile is located subparallel to the sumatran trench at a distance of 32 66 km faulting of the entire sedimentary section strike slip deformation sometimes accompanied by a dip slip component is imaged over two fracture zones of the extinct wharton spreading center that prior studies have shown to be reactivated as left lateral faults the western fracture zone is associated with a wide region of strong basement topography a difference in crustal thickness of 1 5 km and an age offset of 9 ma the epicenters of the 11 april 2012 mw 8 6 great strike slip earthquake its mw 7 2 foreshock and mw 8 2 aftershock align along this major structure 100 km south of the profile intersection our high quality long offset seismic reflection data also reveal bright dipping reflections extending down to a maximum of 24 km into the oceanic mantle 37 km below sea level apparent dips are mostly 25 35 corresponding to 30 55 along either n s to nne ssw or e w to wnw ese directions which encompass the directions of plate fabric and nodal planes of the mw 8 6 event we suggest that these enigmatic reflections arise from presently inactive dip slip fault planes reaching for the deepest ones to the base of the brittle layer possible origins include extension related to plate bending or an episode of now inactive thrust type deformation reactivating paleonormal faults similar to that taking place in the central indian basin

an extensive region of off ridge normal faulting earthquakes in the southern indian ocean an unusually large number of off ridge earthquakes have occurred within a broad region astride the southeast indian ridge the source mechanisms of nine of these earthquakes in lithosphere from 4 to 27 m y old have been determined with a formal inversion technique based on matching observed and synthetic p and sh waves all events occur in the oceanic mantle from 8 to 22 km below the seafloor the seismic moment and duration of faulting obtained from the inversion constrain the stress drop to lie between a few tens of bars and a few hundred bars for most of the events all of the off ridge earthquakes are characterized by normal faulting mechanisms with the t axes nearly parallel to the nearby ridge axis in sharp contrast to typical mid ocean ridge or intraplate earthquakes a variety of possible tectonic processes which might produce normal faulting in young oceanic lithosphere are considered as possible causes including bending stresses thermal stresses of various origins differential subsidence at a fracture zone off ridge volcanism latitudinal plate motions on a nonspherical earth basal shear stress from small scale convection and plate wide perturbations of the stress field due to the continental collision between india and asia no single mechanism is adequate to explain all the observed off ridge normal faulting earthquakes an apparent asymmetry in the observed seismicity with respect to the ridge suggests that the earthquakes on the antarctic and indian plates are caused by different processes the antarctic plate events can be satisfactorily attributed to the release of thermal and bending stresses associated with a residual depth anomaly between the kerguelen plateau and the southeast indian ridge a region which has been suggested as the site of a horizontal pipe for flow in the asthenosphere from the kerguelen hot spot to the vicinity of amsterdam and st paul islands on the southeast indian ridge the off ridge earthquakes in the indian plate are speculatively attributed to part of the plate wide response of the lithosphere to the ongoing continental collision

depth determination for shallow teleseismic earthquakes methods and results the depths of moderate sized shallow earthquakes can be routinely determined to an accuracy of several kilometers using teleseismic data alone making it possible to determine the vertical positions of earthquakes within the lithosphere this capability provides a valuable tool for plate tectonic studies since earthquake depths can be used to constrain lithospheric thermal and mechanical structure at plate boundaries and in intraplate regions two basic techniques are used for depth analyses surface wave spectra can be used to determine focal depths as mode excitation reflects the behavior of the eigenfunctions with depth the primary limitation on such studies stems from lateral heterogeneity of velocity structure the waveforms of body waves are also diagnostic of focal depth which controls the time separation between the direct arrival and near source surface reflections these studies can be limited by a partial trade off between depth and source time function duration the reliability of the body wave modeling approach now in general use is shown by excellent agreement between depths determined by different investigators using different algorithms the depth determination is robust to typical uncertainties in focal mechanism and near source structure the trade off with source time function duration generally does not produce major difficulties for small events ms 6 5 for larger events the trade off can be resolved using a approach in which for a given depth the time function yielding the best fit to a suite of seismograms is found by deconvolution deconvolution at a series of depths yields a misfit function whose minimum indicates the focal depth tests with synthetic data show that the deconvolution process yields reliable depth estimates even given uncertainties in focal mechanism and near source structure it successfully handles multiple sources moderate sized finite sources and horizontally propagating ruptures good results are obtained for vertically propagating ruptures until the fault area becomes so large that waveforms differ significantly from the point source approximation a number of important tectonic results have emerged from studies using these depth determination methods the maximum depth of oceanic intraplate seismicity increases with lithospheric age and is approximately bounded by the 750 c isotherm this depth roughly equals the flexural thickness of the lithosphere but is much less than the depth to the low velocity zone indicated by surface wave dispersion the maximum depth of continental intraplate seismicity is also temperature limited but by a lower temperature these observations are consistent with the rapid weakening of the appropriate rocks with depth predicted by standard temperature dependent rheologies the maximum depth of oceanic transform seismicity corresponds to an isotherm of about 400 c this temperature is lower than would be predicted from the intraplate results and may indicate that transforms are either hotter or weaker than expected the depths of ridge crest earthquakes large enough for teleseismic analysis are extremely shallow 0 8 km the depth distribution of seismicity in continental normal faulting regions provides constraints on the nature of the extension process at subduction zones precise depth determinations can resolve the upper and lower flexural regions in the bending downgoing plate precisely locate the plate interface and map the vertical extent and position of faulting in large earthquakes

the production of north atlantic deep water sources rates and pathways updating an earlier account by dickson et al 1990 this paper reviews the initial development phase of north atlantic deep water nadw production from the points where the dense inflows from nordic seas cross the greenland scotland ridge to the point off south greenland where the buildup of new production appears almost complete in particular three long term current meter arrays totaling 91 instruments and set at 160 km intervals south from the denmark strait sill are used to validate earlier short term arrays by others and in combination with these earlier arrays to describe the downstream evolution of mean speed depth and entrainment the variability of the overflow current in space and time and the likely contribution of the other three main constituents of nadw production at densities greater than 27 8 from the points of overflow 5 6 sv the transport within this range increases by entrainment and confluence with other contributory streams to around 13 3 sv at cape farewell while recirculating elements prevent us from determining the net southgoing transport a nadw transport of this order appears consistent with recent estimates of net abyssal flow passing south through the north and south atlantic

characteristics of ocean waters reaching greenland s glaciers interaction of greenland s marine terminating glaciers with the ocean has emerged as a key term in the ice sheet mass balance and a plausible trigger for their recent acceleration our knowledge of the dynamics however is limited by scarcity of ocean measurements at the glacier ocean boundary here data collected near six marine terminating glaciers 79 north kangerdlugssuaq helheim and petermann glaciers jakobshavn isbrae and the combined sermeq kujatdleq and akangnardleq are compared to investigate the water masses and the circulation at the ice ocean boundary polar water of arctic origin and atlantic water from the subtropical north atlantic are found near all the glaciers property analysis indicates melting by atlantic water aw found at the grounding line depth near all the glaciers and the influence of subglacial discharge at depth in summer aw temperatures near the glaciers range from 4 58c in the southeast to 0 168c in northwest greenland consistent with the distance from the subtropical north atlantic and cooling across the continental shelf a review of its offshore variability suggests that aw temperature changes in the fjords will be largest in southern and smallest in northwest greenland consistent with the regional distribution of the recent glacier acceleration

wind driven currents in the tropical pacific abstract an analysis is made of the ensemble mean ageostrophic near surface circulation measured by 1503 lagrangian drifters drogued to 15 m depth in the tropical pacific between 1987 and 1994 it was found that the physical model of the wind driven currents in a weakly stratified upper layer in which the richardson number remains near unity accounts for 40 of the vector variance of the observations in such a model the amplitude of the current is proportional to u n f 1 2 and the depth scale of the wind driven layer is proportional to u n f 1 2 when the ageostrophic currents at 15 m depth are binned by the scaled ekman depth a net rotation of 0 87 radians was observed through the layer depth these measurements suggest that the vertical austausch coefficient of the upper ocean is proportional to u2 n ekman proposed such a model based on two reports of wind driven currents in 1905 at widely separated latitudes

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

new insights from seismic tomography on the complex geodynamic evolution of two adjacent domains gulf of cadiz and alboran sea 1 in this study we present a three dimensional p wave upper mantle tomography model of the southwest iberian margin and alboran sea based on teleseismic arrival times recorded by iberian and moroccan land stations and by a seafloor network deployed for 1 year in the gulf of cadiz area during the european commission integrated observations from near shore sources of tsunamis towards an early warning system ec nearest project the three dimensional model was computed down to 600 km depth the tomographic images exhibit significant velocity contrasts as large as 3 confirming the complex evolution of this plate boundary region prominent high velocity anomalies are found beneath betics alboran sea off shore southwest portugal and north portugal at sublithospheric depths the transition zones between high and low velocity anomalies in southwest and south iberia are associated to the contact of oceanic and continental lithosphere the fast structure below the alboran sea granada area depicts an l shaped body steeply dipping from the uppermost mantle to the transition zone where it becomes less curved this anomaly is consistent with the results of previous tomographic investigations and recent geophysical data such as stress distribution gps measurements of plate motion and anisotropy patterns in the atlantic domain under the horseshoe abyssal plain the main feature is a high velocity zone found at uppermost mantle depths this feature appears laterally separated from the positive anomaly recovered in the alboran domain by the interposition of low velocity zones which characterize the lithosphere beneath the southwest iberian peninsula margin suggesting that there is no continuity between the high velocity anomalies of the two domains west and east of the gibraltar strait

ocean to shelf signal transmission a parameter study 1 oceanic signal transmission onto and across the continental shelf to the coast is investigated focusing on pressure and surface elevation the model used represents a uniform cross slope section on an f plane with stratification along shelf wave number and oscillatory frequency inclusion of beta and probably a fully three dimensional numerical model would be necessary to treat all forms of oceanic signal at the model s oceanic boundary care is needed for the prescription of the oceanic signal to be physically realistic then substantial transmission across the slope and shelf is limited to 1 large response near a dispersion relation for a coastal trapped wave and 2 large along shelf scale relative to a frictional decay distance for coastal trapped mode 1 that is friction aids signal transmission as a consequence coastal gauges are likely to be effective monitors of only the largest scale oceanic motion typically thousands of kilometers

pathways of inflow and dispersion of warm waters in the nordic seas 1 in this study we use 22 acoustically tracked rafos floats to examine the routes and spreading of warm north atlantic waters entering the norwegian sea between iceland and the faroes the majority of floats crossed the iceland faroe ridge at the eastern end where it is deepest they joined the iceland faroe front but rather than continue north with the outer branch of the norwegian atlantic current into the nordic seas most of them jumped over to the inner branch which continues the inflow through the faroe shetland channel northeast over the voring plateau toward the lofoten basin indeed 17 floats whether deployed near iceland or the faroes did so only 2 floats continued north along the outer branch despite the small numbers these results highlight 1 the strong influence of topography on flow patterns 2 the strong crossover of iceland faroes waters to the inner branch and 3 the rapid and structured spreading into the nordic seas

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

digital isochrons of the world s ocean floor we have created a digital age grid of the ocean floor with a grid node interval of 6 arc min using a self consistent set of global isochrons and associated plate reconstruction poles the age at each grid node was determined by linear interpolation between adjacent isochrons in the direction of spreading ages for ocean floor between the oldest identified magnetic anomalies and continental crust were interpolated by estimating the ages of passive continental margin segments from geological data and published plate models we have constructed an age grid with error estimates for each grid cell as a function of 1 the error of ocean floor ages identified from magnetic anomalies along ship tracks and the age of the corresponding grid cells in our age grid 2 the distance of a given grid cell to the nearest magnetic anomaly identification and 3 the gradient of the age grid i e larger errors are associated with high age gradients at fracture zones or other age discontinuities future applications of this digital grid include studies of the thermal and elastic structure of the lithosphere the heat loss of the earth ridge push forces through time asymmetry of spreading and providing constraints for seismic tomography and mantle convection models

deep convection in the labrador sea as observed by lagrangian floats abstract during the winters of 1997 and 1998 a total of 24 lagrangian floats were deployed in the labrador sea these floats were designed to match the buoyancy and compressibility of seawater they measured temperature and three dimensional position pressure for vertical position and rafos acoustic tracking for latitude and longitude as they followed water motions three dimensionally this data provides direct observation of mixed layer depth and excellent estimates of vertical velocity floats were repeatedly carried across the convecting layer by vertical velocities averaging several centimeters per second with vertical excursions of up to one kilometer in the horizontal several scales of eddy motion were resolved as was a possible float predilection toward remaining in water preconditioned for convection heat flux estimates from this data reveal entrainment and surface heat fluxes similar in magnitude the mixed layer acts as a vertical conveyor belt of temperature transporting heat from depth

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

role of greenland freshwater anomaly in the recent freshening of the subpolar north atlantic the cumulative greenland freshwater flux anomaly has exceeded 5 000 km3 since the 1990s the volume of this surplus freshwater is expected to cause substantial freshening in the north atlantic analysis of hydrographic observations in the subpolar seas reveals freshening signals in the 2010s the sources of this freshening are yet to be determined in this study the relationship between the surplus greenland freshwater flux and this freshening is tested by analyzing the propagation of the greenland freshwater anomaly and its impact on salinity in the subpolar north atlantic based on observational data and numerical experiments with and without the greenland runoff a passive tracer is continuously released during the simulations at freshwater sources along the coast of greenland to track the greenland freshwater anomaly tracer budget analysis shows that 44 of the volume of the greenland freshwater anomaly is retained in the subpolar north atlantic by the end of the simulation this volume is sufficient to cause strong freshening in the subpolar seas if it stays in the upper 50 100 m however in the model the anomaly is mixed down to several hundred meters of the water column resulting in smaller magnitudes of freshening compared to the observations therefore the simulations suggest that the accelerated greenland melting would not be sufficient to cause the observed freshening in the subpolar seas and other sources of freshwater have contributed to the freshening impacts on salinity in the subpolar seas of the freshwater transport through fram strait and precipitation are discussed

preliminary results from directly measuring middepth circulation in the tropical and south pacific as part of the world ocean circulation experiment 300 autonomous lagrangian circulation explorer floats were deployed in the tropical and south pacific to measure the general circulation at 900 m depth most floats measured average currents over 25 submerged days between ascents to the surface for locating and data relay by the end of 1997 over 12 500 observations spanning 840 float years were obtained accuracy of the average velocity is limited by variability some of which is found to arise from steady flows with spatial variations smaller than averaging scales observed 25 day velocities are serially uncorrelated except near the equator where energetic zonal variability has seasonal timescales and appears to be described by a data assimilating ocean circulation model run by the national centers for environmental prediction space time averages of float velocities disclose a general pattern of middepth flow that resembles the surface circulation with the strongest flows of o 3 cm s in the deep antarctic circumpolar current and east australian current the weaker elements of the flow including an interior subtropical circulation with o millimeters per second flows are described by an objective analysis whose accuracy is limited by sampling noise rather than uncertainty of the analysis parameters the subtropical circulation has a gyres within a gyre structure including boundary currents along australia and east of new zealand and a concentrated equatorial limb with surprising strength in the western basin this current is also involved in a tropical gyre with generally eastward flow along the equator in the western basin at least because of strong seasonal scale variability the equatorial zonal currents are not well measured yet but data are still being accumulated comparison with reid s 1997 absolute circulation shows more areas of agreement than of disagreement

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

a rare great earthquake on an oceanic fossil fracture zone first motion solution found in this study and has a strike consistent with the fracture zone north of the bend the southern fault plane with strike 178 d ip 54 and rake 65 has a strike consistent with the portion of the fracture zone to the south of the bend and has a dip which can be explained by the style of deformation that the region is undergoing the centroid moment tensor solution of the broad band model is calculated and found to be consistent with the region of low misfit in mantle wave solution space the broad band solution has a moment of 1 53 10 21 nm mw 8 1 again consistent with the mantle wave data slip propagated bilaterally with an approximate rupture velocity of 3k ms 1 80 per cent of local shear wave speed the rupture front is less well resolved to the south of the epicentre than to the north the majority 75 per cent of moment originated from slip on the northern fault the broad band data requires significant slip below the oceanic moho with as much as 70 per cent of moment due to slip in the brittle uppermost mantle in the preferred model

quantifying atlantic water transport to the nordic seas by remote sensing abstract in this study the variability of atlantic water aw entering the nordic seas from the north atlantic through the passage between iceland the faroe islands and scotland has been investigated the poleward transport of this warm aw is a key component in maintaining a relatively mild climate in the northwestern europe satellite remote sensing datasets from altimetry and the gravity field and steady state ocean circulation explorer goce mission in combination with surface drifters fixed current meter and hydrographic data are used the high resolution mean dynamic topography mdt is shown to resolve the time invariant surface currents in the inflow region in addition to the improved mdt we take benefit of the new reprocessed sea level anomaly data in the estimation of absolute dynamic topography analysis of the monthly surface velocities from 1993 to 2016 demonstrates significant influence of the large scale atmospheric forcing associated with the north atlantic oscillation nao furthermore a significant increase in surface velocities along the slope current front current and the norwegian coastal current are found during winter finally combining altimetry with hydrographic data we demonstrate that the variability in surface velocities of the inflow region is also reflected in the deeper layers and that altimetry therefore can be used to monitor the variability of the poleward transport of aw in this region

characteristics and dynamics of two major greenland glacial fjords the circulation regimes of two major outlet glacial fjords in southeastern greenland sermilik fjord sf and kangerdlugssuaq fjord kf are investigated using data collected in summer 2009 the two fjords show similar flow patterns with a time dependent vertically sheared flow structure dominating over the background estuarine flow driven by buoyancy input we show that this time dependent flow is consistent with circulation induced by density interface fluctuations at the fjord mouth often referred to as intermediary circulation one difference between the fjords is that the hydrographic and velocity structure below a surface modified layer is found to be three layer in kf in summer compared to two layer in sf outside each fjord large scale geostrophic currents dictate the stratification at the mouth although the way in which these large scale flows impinge on each fjord is distinct combining the observations with estimates from existing theories we find the magnitudes of the estuarine qe and intermediary qi circulation and show that qi qe although along fjord winds can also be significant we expect that the critical parameter determining qi qe is the sill depth compared to the fjord depth with shallower sills corresponding to weaker intermediary circulation finally we discuss the implications of strong intermediary circulation on calculating heat transport to the glacier face and its potential feedbacks on the background circulation in these highly stratified estuaries

wind driven motions in the northeast pacific as measured by lagrangian drifters abstract analysis is presented of the time dependent motion of 47 surface drifters in the northeast pacific during fall 1987 and 16 drifters in fall and winter 1989 90 the drifters were designed at 15 m depth and were designed to have wind produced slips less than 2 cm s 1 for wind speeds up to 20 m s 1 the coherence of velocity and local wind is presented for motions with periods between 1 day and 40 days for periods between 5 and 20 days drogue motion at 15 m depth is found to be highly coherent with local wind with an average phase of 70 to the right of the rotating wind vector these results differ from analyses of fgge type drifters as reported by mcnally et al and niiler in the same area a model of wind produced slip as a function of drifter design is used to provide a possible explanation of the differences a linear regression which accounts for 20 40 of the current variance gives water motion al 0 5 of wind speed and 68 to the right of the wind vector assuming an ekman type balance

measured volume heat and salt fluxes from the atlantic to the arctic mediterranean 1 the flow of warm and saline atlantic water towards the arctic crosses the greenland scotland ridge in three current branches since the mid 1990 s extensive monitoring with quasi permanent moorings and regular ctd cruises has been in operation on three sections crossing the branches averaged over the years 1999 to 2001 values of volume heat relative to 0 c and salt flux due to the total atlantic inflow across the greenland scotland ridge into the nordic seas are estimated as 8 5 sv 1 sv 106 m3 s 1 313 1012 w and 303 106 kg s 1 in this period the average temperature and salinity of the atlantic inflow were 8 5 c and 35 25 respectively within the observational uncertainty we do not find any significant seasonal variation of the volume flux but a negative correlation between the inflow flux through the faroe shetland channel and through the other two gaps was indicated

teleseismic search for slow precursors to large earthquakes some large earthquakes display low frequency seismic anomalies that are best explained by episodes of slow smooth deformation immediately before their high frequency origin times analysis of the low frequency spectra of 107 shallow focus earthquakes revealed 20 events that had slow precursors 95 percent confidence level 19 were slow earthquakes associated with the ocean ridge transform system and 1 was a slow earthquake on an intracontinental transform fault in the east african rift system these anomalous earthquakes appear to be compound events each comprising one or more ordinary fast ruptures in the shallow seismogenic zone initiated by a precursory slow event in the adjacent or subjacent lithosphere

laboratory simulation of exchange through fram strait laboratory experiments and theory were conducted to observe the flow patterns and transport in both buoyancy driven and wind driven rotating fluids in lock exchange experiments water with one density flows into a second basin after a sliding gate is removed water of a second density flows back into the first basin the size and location of the currents for various values of density difference rotation rate and assorted sidewall geometries was recorded volume flux of the fluid was also measured and compared with a theory for lock exchange flow of a rotating fluid in a separate group of experiments with a passive upper layer easterly winds like those in the arctic ocean drive the upper level water into the arctic ocean and therefore oppose the buoyant exchange westerly winds would drive the water out of the arctic ocean this indicates that the exchange between the arctic ocean and the greenland norwegian sea is likely to be driven by buoyancy rather than by driven by wind crude estimates of the volumetric and fresh water exchange rate from the lock exchange formulas are compared with observed ocean fluxes and approximate agreement is found

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

rupture characteristics of the 2003 mw 7 6 mid indian ocean earthquake implications for seismic properties of young oceanic lithosphere 1 analysis of broadband seismograms from the 15 july 2003 large earthquake m 7 6 in the central indian ocean reveals an unusual source process the source duration of longer than a minute is more than twice as long as expected from earthquake scaling relations yet 80 of the moment release occurred in two energetic asperities near the end of the rupture these two asperities were located in lithosphere with an age of 7 ma or greater a previous study has suggested that strike slip earthquakes in oceanic lithosphere having much longer than expected source durations also have a slow dissipative rupture process characterized by low radiated seismic energy and therefore low apparent stress we find no evidence for a slow rupture process to the 2003 earthquake instead the long duration appears to be due only to nucleation close to the actively spreading carlsberg ridge in lithosphere younger than 7 ma younger oceanic lithosphere may be able to generate small to moderate earthquakes but be unable to sustain slip in a large event due to steady release of strain in aseismic creep events large strike slip earthquakes within oceanic lithosphere may occur only in the central portions of long transform faults or in intraplate regions rupturing energetic asperities like those that failed in the mid indian ocean earthquake and leading to the observation that oceanic strike slip earthquakes have the largest apparent stresses among the global population of shallow earthquakes

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

the arctic front in the greenland sea during february 1989 hydrographic and biological observations high resolution hydrographic and biological observations in the arctic frontal regime were made in february 1989 along 74 45 n the frontal zone was found to contain four individual frontal interfaces these fronts were a result of the large scale convergence of the currents around the greenland sea gyre bringing together arctic and polar surface waters and two modes of atlantic surface water the distribution of arctic and atlantic copepod species as well as the composition of their developmental stages showed a strong correlation with the distribution of water masses whereby the frontal interfaces acted as biogeographic boundaries whereas the fronts bounding the polar water reached only to a depth of about 100 m the fronts bordering the atlantic water masses could be observed to depths of 600 m at subsurface levels a core of atlantic intermediate water from the jan mayen current was observed the properties of this water type can be explained quantitatively from double diffusive exchange with the overlying water the mixing across the fronts was found to be dominated by fluxes of heat salt and copepods toward the central greenland sea gyre

lagrangian eddy scales in the northern atlantic ocean eddy time and length scales are calculated from surface drifter and subsurface float observations in the northern atlantic ocean outside the energetic gulf stream subsurface timescales are relatively constant at depths from 700 m to 2000 m length scale and the characteristic eddy speed decrease with increasing depth below 700 m but length scale stays relatively constant in the upper several hundred meters of the gulf stream it is suggested that this behavior is due to the lagrangian sampling of the mesoscale field in limits set by the eulerian eddy scales and the eddy kinetic energy in high energy regions of the surface and near surface north atlantic the eddy field is in the frozen field lagrangian sampling regime for which the lagrangian and eulerian length scales are proportional however throughout much of the deep ocean interior the eddy field may be in the fixed float regime for which the lagrangian and eulerian timescales are nearly equal this does not necessarily imply that the deep interior is nearly linear as fixed float sampling is possible in a flow field of o 1 nonlinearity

reconstruction of hydrographic changes in the southern norwegian sea during the past 135 kyr and the impact of different foraminiferal mg ca cleaning protocols uit arctic university of norway the mohn foundation the research council of norway through its centres of excellence funding scheme project grant number 223259

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

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

postglacial vegetation and climate of the cascade range central oregon abstract pollen data from two sites provide information on the postglacial vegetation and climate history of the cascade range indian prairie in the western cascade range was colonized by subalpine forests of pinus picea and tsuga and open meadows prior to ca 12 400 14 c yr b p the treeline lay 500 to 1000 m below its modern elevation and conditions were cooler than at present from ca 12 400 to ca 9950 14 c yr b p abies became important and the forest resembled that presently found at middle elevations in the western cascade range the pollen record implies a rise in treeline and warmer conditions than before from ca 10 000 to 4000 4500 14 c yr b p conditions that were warmer and effectively drier than today led to the establishment of a closed forest composed of pseudotsuga abies and at lower elevations quercus and corylus during this period gold lake bog in the high cascades was surrounded by closed forest of pinus and abies the early holocene pollen assemblages at both indian prairie and gold lake bog lack modern analogues and it is likely that greater than present summer radiation fostered unique climatic conditions and vegetation associations at middle and high elevations in the late holocene beginning ca 4000 4500 14 c yr b p cooler and more humid conditions prevailed and the modern vegetation was established a comparison of these sites with others in the pacific northwest suggests that major patterns of vegetational change at individual sites were a response to large scale changes in the climate system that affected the entire region

bathymetric prediction from dense satellite altimetry and sparse shipboard bathymetry the southern oceans south of 30 s are densely covered with satellite derived gravity data track spacing 2 4 km and sparsely covered with shipboard depth soundings hundreds of kilometers between tracks in some areas flexural isostatic compensation theory suggests that bathymetry and downward continued gravity data may show linear correlation in a band of wave lengths 15 160 km if sediment cover is thin and seafloor relief is moderate at shorter wave lengths the gravity field is insensitive to seafloor topography because of upward continuation from the seafloor to the sea surface at longer wavelengths isostatic compensation cancels out most of the gravity field due to the seafloor topography we combine this theory with wiener optimization theory and empirical evidence for gravity noise to signal ratios to design low pass and band pass filters to use in predicting bathymetry from gravity the prediction combines long wavelengths 160 km from low pass filtered soundings with an intermediate wavelength solution obtained from multiplying downward continued band pass filtered 15 160 km gravity data by a scaling factor s s is empirically determined from the correlation between gravity data and existing soundings in the 15 160 km band by robust regression and varies at long wave lengths we find that areas with less than 200 m of sediment cover show correlation between gravity and bathymetry significant at the 99 level and s may be related to the density of seafloor materials in these areas the prediction has a horizontal resolution limit of 5 10 km in position and is within 100 m of actual soundings at 50 of grid points and within 240 m at 80 of these in areas of very rugged topography the prediction underestimates the peak amplitudes of seafloor features images of the prediction reveal many tectonic features not seen on any existing bathymetrie charts because the prediction relies on the gravity field at wavelengths 160 km it is insensitive to errors in the navigation of sounding lines but also cannot completely reproduce them therefore it may be used to locate tectonic features but should not be used to assess hazards to navigation the prediction is available from the national geophysical data center in both digital and printed form

the east greenland coastal current structure variability and forcing abstract the subtidal circulation of the southeast greenland shelf is described using a set of high resolution hydrographic and velocity transects occupied in summer 2004 the main feature is the east greenland coastal current egcc a low salinity high velocity jet with a wedge shaped hydrographic structure characteristic of other surface buoyancy driven currents the egcc was observed along the entire greenland shelf south of denmark strait while the transect north of the strait showed only a weak shelf flow this observation in conjunction with water mass considerations and other supporting evidence suggests that the egcc is an inner branch of the east greenland current egc that forms south of denmark strait it is argued that bathymetric steering is the most likely reason why the egc apparently bifurcates at this location repeat sections occupied at cape farewell between 1997 and 2004 show that the alongshelf wind stress can have an influence on the structure and strength of the egcc and egc on timescales of 2 3 days accounting for the wind induced effects the volume transport of the combined egcc egc system is roughly constant 2 sv over the study domain from 68 n to cape farewell near 60 n the corresponding freshwater transport increases by roughly 60 over this distance 59 96 msv referenced to a salinity of 34 8 this trend is consistent with a simple freshwater budget of the egcc egc system that accounts for meltwater runoff melting sea ice and icebergs and net precipitation minus evaporation

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

coherent eddies in the labrador sea observed from a mooring abstract during june november 1994 a mooring in the central labrador sea near the former ocean weather station bravo recorded a half dozen anomalous events that prove to be two different types of coherent eddies comparisons with simple analytical models are used to classify these events as coherent eddies on the basis of their velocity signatures the first clear examples of long lived convectively generated eddies are reported these four small radius 5 15 km eddies are exclusively anticyclonic with cold fresh middepth potential temperature and salinity s cores surrounded by azimuthal currents of 15 cm s 1 their s properties identify them unambiguously as the products of wintertime deep convection in the interior labrador sea compared with eddies in other regions these anticyclones are unusual for their strong surface expressions and composite s cores two warm cyclones are also seen these are larger radius 15 km than the anticyclones and about as energetic currents 15 cm s 1

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

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

coherent sea level fluctuations along the global continental slope signals in sea level or more properly sub surface pressure ssp sea level corrected for the inverse barometer effect are expected to propagate rapidly along the continental slope due to the effect of sloping topography on wave modes resulting in strongly correlated ssp over long distances observations of such correlations around the arctic and antarctic are briefly reviewed and then extended using satellite altimetry to the rest of the global continental slope it is shown that such long distance correlations are common especially in extra tropical regions simple correlations from altimetry cannot however establish the wave speed or whether waves are responsible for the correlations as opposed to large scale coherence in the forcing a case study around south america is used to highlight some of the complications and is found to strengthen the case for the importance of wave modes in such long distance ssp coherence although more detailed in situ data are required to resolve the cause of the correlations

structure and variability of the west greenland current in summer derived from 6 repeat standard sections abstract six historical sections across the west greenland current are examined three sections have been regularly occupied since the late 1950s while the three southern ones have been taken since 1984 significant variability is observed for the freshwater core of the coastal current on the shelf with salinity varying by over 3 units between years there is also significant variability in the shape and offshore position of the main shelf break front leading to large variability in eulerian velocities significant presence of irminger water is seen during the 1960s and the 2000s being found right across the sections in recent years maximum mean transport relative to the 34 8 isohaline of 5 5 3 9 sv relative to 700 db for 1984 2005 is observed at the cape desolation section transports decrease to the north with the majority of the exchange with the interior of the labrador sea occurring between cape desolation and fylla bank inter decadal transport variability is observed at fylla bank while a decline in transports since peaks in the early 1990s is seen at cape farewell and cape desolation freshwater transport is largest at cape desolation with a mean summer transport of 60 2 20 5 msv freshwater transport increases slightly between cape farewell and cape desolation and we suggest it is related to local discharge by glaciers into juliannehaab bight as well as the melting of sea ice we also find that years of high greenland ice cap melt are consistently associated with years of high freshwater transport at cape desolation suggesting a portion of the freshwater transport of the west greenland current may be associated with melt from the greenland ice sheet finally significantly enhanced freshwater transports 33 msv at cape desolation compared to the long term mean are seen in 2008 probably a signature of the record arctic ocean ice melt and export in 2007

north atlantic surface circulation during the 1990 s observed with satellite tracked drifters a new compilation of lagrangian velocity observations describes the state of the north atlantic surface circulation during the 1990s gridded fields of velocity and eddy kinetic energy eke are constructed from trajectories of more than 1500 15 m drogued satellite tracked surface drifters in service between january 1990 and december 1999 this time period overlaps a coordinated field study of circulation and variability in the north atlantic completed between 1996 2000 as part of the world ocean circulation experiment we describe the construction of a self consistent drifter climatology present decadal mean quasi eulerian velocity and eke fields computed on a 1 grid and compare these results with contemporary satellite measurements detailed discussion of the inferred surface circulation is focused on three regions 1 the gulf stream and north atlantic current 2 the labrador sea and subpolar gyre and 3 the caribbean sea the swiftest drifter motions were found in the equatorial region and along the tropical subtropical and subpolar western boundaries the maximum instantaneous speed determined from a single quality controlled and filtered drifter observation was 273 cm s 1 in the gulf stream southeast of cape cod the highest eke value in the north atlantic 2790 cm2 s 2 was found in the gulf stream just downstream of the new england seamounts over most of the atlantic basin drifter derived eke values were found to be o 100 cm2 s 2 higher than corresponding values derived from satellite altimetry in the labrador sea a region of sharply elevated eke appears to be geographically related to the localized ejection of drifters and by extension mass and kinetic energy from the energetic west greenland current between 60 and 62 n when compared to drifter measurements made in the late 1970s our results suggest but do not statistically confirm an enhancement and slight northward shift of the zonal gulf stream extension such a shift is consistent in sign with expectations based on observed interdecadal variations in wind stress and subtropical gyre potential energy associated with the north atlantic oscillation

upper ocean heat content in the nordic seas 1 seven years of temperature profiles are obtained from the argo float project and are used to study the vertically integrated heat content for the nordic seas which is broken up into the norwegian basin greenland sea lofoten region and iceland plateau the world ocean atlas 2005 woa05 is used as the climatological baseline for temperature and hence heat content temporally and spatially averaged temperature profiles within the norwegian and iceland basins show good agreement between the argo and woa05 data sets for the greenland and lofoten basins the woa05 data show cooler surface temperatures by 1 2 c but still lie within 1 standard deviation of each other over the 7 year period the argo float data show circulation within each of the basins that is counterclockwise and some of the floats eventually disperse toward the outer edges of the basins vertically integrated heat content from 0 to 1200 m shows similar characteristics as the woa05 results including the timing and strength of the seasonal variability the anomalous heat content for the greenland and norwegian sea basins is calculated in depth bins of 400 m the greenland sea shows a warming trend over the 7 years of study which corresponds to a temperature increase of 4 1 0 3 10 2 c yr the norwegian sea basin shows interannual variability in heat content for the surface layer 0 400 m that may be related to the north atlantic oscillation nao during an nao phase the norwegian basin shows a warm phase and during an nao phase the norwegian basin is in a cold phase the correlation is small r 0 32 but different from zero correlation only at the 90 level implying that the variability in the ahc may be due to 1 local atmospheric forcing and hence changes in heat loss 2 atmospheric pressure differences that are not resolved by the nao index and 3 exchange of heat with the basin boundaries

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

near surface mean circulation and kinetic energy in the central north atlantic from drifter data an analysis of a large drifting buoy data set is presented the objective is to obtain a self contained description of the properties of the near surface circulation drogue depth 100 m in the central north atlantic ocean independent of hydrographic data a necessary preanalysis step was the removal of all data from undrogued buoys from the data set the physical parameters of the circulation were deduced by averaging the remaining data in 2 3 boxes the minimum amount of data which is necessary to get statistically stable results was determined by an empirical quality criterion all important mean currents in the investigation area are reproduced by the near surface mean velocity field a separation of the mean velocity field into a nondivergent and an irrational part shows that the flow field is almost nondivergent the distribution of eddy kinetic energy is concentrated along the mean currents and provides the largest part of the total kinetic energy but there are regional variations energy from inertial movements dominates the high frequency part of the kinetic energy its distribution is very patchy the analysis of the reynolds stress terms shows an energy transfer from the eddy field to the mean circulation in the vicinity of the north atlantic current

variability of the atlantic inflow to the nordic seas and its causes inferred from observations of sea surface height 1 we investigate the potential to use sea surface height observed with satellites and tide gauges to explore and to estimate the variability of volume transport of atlantic water to the nordic seas it is shown that the variability of the atlantic inflow to the nordic seas over the iceland faroe ridge faroe current primarily responds to an oceanic regime dominated by steric height changes in the interior nordic seas in contrast variations in the norwegian atlantic slope current measured at the svinoy section are largely driven by direct wind forcing using linear regression analysis volume transports anomalies were successfully modeled from the leading modes of altimeter derived sea surface height and reconstructed back in time using sea surface height observations from tide gauges the reconstructions explain 22 and 38 of the observed variability in the faroe and svinoy currents respectively for the svinoy current the reconstruction indicates that the volume transport variability is typically of the order 1 sv high inflow around 1983 and low inflow around 1987 coincide with times when respectively warm and cold anomalies passed through the system

a freshwater jet on the east greenland shelf in august 1997 rrs discovery cruise 230 world ocean circulation experiment woce section a25 ran a hydrographic section into cape farewell on the southern tip of greenland the closest approach to the shore was 2 nm in a water depth of 160 m over the east greenland shelf analysis of the hydrographic data conductivity temperature depth ctd vessel mounted acoustic doppler current profiler and thermosalinograph has revealed a current flowing southwestward 15 km wide 100 m deep and centered 10 km offshore we believe it to be driven by meltwater runoff from greenland this feature which we call the east greenland coastal current egcc carries a little less than 1 sv 106 m3 s 1 with peak current speeds of 1 m s 1 at the surface the center of the egcc lies on a salinity front with maximum salinity contrast 4 practical salinity units psu between coast and shelf break and between surface and bottom a spot value of freshwater transport is 0 06 sv 1800 km3 yr 1 which is equivalent to 30 of the arctic freshwater gain the presence of the egcc and its continuity up the east greenland coast as far as denmark strait is confirmed in satellite sea surface temperature images and surface drifter tracks we estimate the sensitivity of its freshwater flux to changes in melt season mean surface air temperature to be 25 per 1 c

currents and mixing in the irminger sea and in the iceland basin on the basis of a hydrographic section from the faeroe islands toward greenland along 62m 0n and the deployment of about 20 satellite tracked buoys it is shown that the irminger current branches at the reykjanes ridge its total transport amounts to 17 18 sv the eastern branch of the irminger current 8 sv turns east and enters the norwegian sea both through the faeroe shetland channel 3 sv and by passing northeast of the faeroe islands maximum speeds of 70 cm s 1 are reached at the outer edge of the east and west greenland current very intensive mixing is observed between the four water masses that flow into the irminger basin stirring by eddies plays a dominant role for strong interleaving subsequent salt fingering and double diffusive layering conditions for these processes are optimal nearly everywhere in the irminger sea

a reassessment of the rupture characteristics of oceanic transform earthquakes 1 we investigate the long period source spectra of oceanic transform earthquakes and find that previously proposed slow rupture components can be explained as artifacts generated by the modeling procedure we use low frequency 20 mhz rayleigh and love waves to calculate the amplitude spectra of five earthquakes on the romanche and chain transform faults in the equatorial mid atlantic ocean we find that errors and approximations in the centroid depth focal mechanism and earth structure at the source have significant effects on the shape of the source spectra if global catalog values and an average crustal model are assumed the spectra exhibit apparent anomalous energy at long periods which has previously been interpreted as a result of slow rupture we recalculate the source spectra using precise independently determined depths and moment tensors and a more realistic oceanic crustal structure in the source region the resulting source spectra are flat at long periods with no indication of anomalous long period energy our results imply that oceanic transform earthquakes do not commonly have detectable slow rupture components

detection of deep overflows with satellite altimetry in situ observations downstream of the sills in the faroe bank channel and denmark strait show large temperature and current variability of the overflows with time scales of a few days these fluctuations are associated with meso scale eddies and have an impact on sea surface height this is confirmed by observations from the topex poseidon and ers 1 2 satellites that show substantial enhancement of eddy kinetic energy and sea level variability immediately down stream of the sills

direct measurements of the mean flow and eddy kinetic energy structure of the upper ocean circulation in the ne atlantic 1 the upper ocean circulation in the sub polar northeast atlantic has been a challenge to quantify due to strong and variable wind forcing and strong and variable deep currents that lead to large uncertainties in the use of the standard dynamical method since 1999 we have been operating an acoustical doppler current profiler on a container vessel that operates between denmark and greenland to repeatedly sample upper ocean currents across the northeast atlantic individual transects exhibit a highly energetic mesoscale variability but ensemble averaging of the sections reveals a striking organization of the mean field along the reykjanes ridge a distinct southward flow along its eastern slope and two clearly defined peaks with seasonal modulation flowing to the north along its western slope higher values of eddy kinetic energy about 150 600 cm2 s 2 are observed along the transect o 1 5 greater than surface drifter estimates

quantifying mesoscale eddies in the lofoten basin the lofoten basin is the most eddy rich region in the norwegian sea in this paper the characteristics of these eddies are investigated from a comprehensive database of nearly two decades of satellite altimeter data 1995 2013 together with argo profiling floats and surface drifter data an automated method identified 1695 1666 individual anticyclonic cyclonic eddies in the lofoten basin from more than 10 000 altimeter based eddy observations the eddies are found to be predominantly generated and residing locally the spatial distributions of lifetime occurrence generation sites size intensity and drift of the eddies are studied in detail the anticyclonic eddies in the lofoten basin are the most long lived eddies 60 days especially in the western part of the basin we reveal two hotspots of eddy occurrence on either side of the lofoten basin furthermore we infer a cyclonic drift of eddies in the western lofoten basin barotropic energy conversion rates reveals energy transfer from the slope current to the eddies during winter an automated colocation of surface drifters trapped inside the altimeter based eddies are used to corroborate the orbital speed of the anticyclonic and cyclonic eddies moreover the vertical structure of the altimeter based eddies is examined using colocated argo profiling float profiles combination of altimetry argo floats and surface drifter data is therefore considered to be a promising observation based approach for further studies of the role of eddies in transport of heat and biomass from the slope current to the lofoten basin

labrador sea boundary currents and the fate of the irminger sea water abstract the general circulation of the labrador sea is studied with a dataset of 53 surface drifters drogued at 15 m and several hydrographic sections done in may 1997 surface drifters indicate three distinct speed regimes fast boundary currents a slower crossover from greenland to labrador and a slow eddy dominated flow in the basin interior mean eulerian velocity maps show several recirculation cells located offshore of the main currents in addition to the cyclonic circulation of the labrador sea above the northern slope of the basin the surface drifters have two preferential paths one between the 1000 m and 2000 m isobaths and the other close to the 3000 m isobath the vertical shear estimated from ctd data supports the presence of two distinct currents around the basin one current more baroclinic flows between the 1000 m and 2000 m isobaths the other one more barotropic flows above the lower continental slope the irminger sea water carried by the boundary currents is altered as it tr

on the spatial structure and temporal variability of poleward transport between scotland and greenland 1 the flow north of warm subtropical water though the northeastern atlantic is known to have many pathways that vary over time here we use a combination of upper ocean current measurements betwe

sea surface height changes in the north atlantic ocean related to the north atlantic oscillation interannual sea surface height ssh variability as measured by the topex poseidon satellite altimeters is investigated for the north atlantic ocean between 1992 and 1998 the ssh variability exhibits a basin wide coherent dipole structure between the subtropical and the subpolar north atlantic the ssh dipole pattern changed sign between 1995 and 1996 coinciding with a change of sign of the north atlantic oscillation nao the large scale ssh pattern is reproduced with an ocean general circulation model and can be traced back to changes in the atmospheric forcing related to the nao the model reveals that the interannual ssh anomalies are mainly caused by changes in the oceanic heat transport which are connected with the response of the large scale ocean circulation to changes in the wind stress curl variations in the local heat flux reinforce these ssh anomalies but are of minor importance

labrador sea water tracked by profiling floats from the boundary current into the open north atlantic fifteen profiling floats were injected into the deep boundary current off labrador they were ballasted to drift in the core depth of labrador sea water lsw at 1500 m depth and were deployed in two groups during march and july august 1997 initially for about three months the floats were drifting within the boundary current and the flow vectors were used to determine the mean horizontal structure of the deep labrador current which was found to be about 100 km wide with an average core speed of 18 cm s 1 north of flemish cap the boundary current encounters complicated topography around orphan knoll and there the lsw outflow splits up into different routes one obvious lsw path is eastward through the charlie gibbs fracture zone and another route is a narrow recirculation toward the central labrador sea a surprising result was that none of the floats were able to follow the boundary current southward to the grand banks area and exit into the subtropics trajectories and temperature profiles of the eastward drifting floats indicate the importance of the north atlantic current for dispersing the floats even at the level of lsw

north atlantic oscillation induced changes of the upper layer circulation in the northern north atlantic ocean 1 hydrographic data of the 1990s along world ocean circulation experiment sections a1e greenland ireland and a2 newfoundland france indicate a redistribution of cold low saline subarctic waters and warm saline subtropical waters in the upper layer of the northern north atlantic within about 2 years after the north atlantic oscillation had turned from a period with strong westerlies until 1995 to a period with weak westerlies in 1996 and 1997 in the latter period subarctic waters spread preferably southward along the continental slope east of newfoundland rather than eastward with the north atlantic current nac into the irminger iceland and west european basins as a consequence the subarctic front and the associated nac shifted eastward in the newfoundland basin where subarctic waters accumulate and westward in the iceland basin where a large warm and saline anomaly was found in 1996 and 1997 indicating a contraction of the subpolar gyre in the irminger basin the anomaly occurred in 1998 and 1999 whereas the cyclonic circulation in the irminger and iceland basins weakened it intensified in the newfoundland basin where a strengthened labrador current retroflection joined the nac this and the increased anticyclonic recirculation of subtropical waters in the newfoundland and west european basins caused a considerable reduction of the northward heat transport across 47 n in the upper layer in 1997 the anticyclonic circulation occurring in the west european basin suggested a northward expansion of the subtropical gyre

the 3 d structure of mesoscale eddies in the lofoten basin of the norwegian sea a composite analysis from altimetry and in situ data

holocene multidecadal to millennial scale variations in iceland scotland overflow and their relationship to climate the nordic seas overflows are an important part of the atlantic thermohaline circulation while there is growing evidence that the overflow of dense water changed on orbital time scales during the holocene less is known about the variability on shorter time scales beyond the instrumental record here we reconstruct the relative changes in flow strength of iceland scotland overflow water isow the eastern branch of the overflows on multidecadal millennial time scales the reconstruction is based on mean sortable silt ss from a sediment core on the gardar drift 60 19 n 23 58 w 2081 m our ss record reveals that the main variance in isow vigor occurred on millennial time scales 1 2 kyr with particularly prominent fluctuations after 8 kyr superimposed on the millennial variability there were multidecadal centennial flow speed fluctuations during the early holocene 10 9 kyr and one prominent minimum at 0 9 kyr we find a broad agreement between reconstructed isow and regional north atlantic climate where a strong weak isow is generally associated with warm cold climate we further identify the possible contribution of anomalous heat and freshwater forcing respectively related to reconstructed overflow variability we infer that ocean poleward heat transport can explain the relationship between regional climate and isow during the middle to late holocene whereas freshwater input provides a possible explanation for the reduced overflow during early holocene 8 10 kyr

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

quantifying flow regimes in a greenland glacial fjord using iceberg drifters funded by the national science foundation grant numbers oce 1130008 arc 0909274 and the university of oregon

holocene sedimentary processes in the andoya canyon system north norway abstract the andoya canyon system is the most pronounced of the ten canyon systems identified on the norwegian continental margin none of these canyon systems is linked to any present active drainage area and are interpreted to have been basically non active since the last glacial maximum and the deglaciation period our knowledge on these canyon systems is however still limited as no high resolution stratigraphical or acoustic data sets are available from these areas the main target for analysing the long term history of the andoya canyon has been to study the distal accumulation part of this system in the lofoten basin the lofoten basin area is characterized by repeated stacks of extensive turbidite units where the details of the stratigraphical succession can be studied in undisturbed settings about 3000 km 2 of high resolution multibeam data em300 along with three gravity cores have been collected from the lofoten basin area the analyses carried out on the cores revealed that the predominant process results in single turbidite units interbedded with thin units of hemipelagic sedimentation the radiocarbon dating revealed that turbidites have been transported through this channel system at least twice during the holocene the two uppermost dated turbidite sequences give a maximum age of 7 9 ka 14 c bp for the lower sequence and an age of ca 4 0 ka 14 c bp for the upper sequence the upper sequence is of a similar age as the traenadjupet slide failure whereas the lower sequence indicates an age close to the storegga slide failure event taking into consideration the erosive lower boundary of that sequence the location of the investigated cores which are far away from both the traenadjupet slide and the storegga slide indicate that the instability in these canyon systems during the holocene period has most probably been influenced by these large scale failure events what triggered the release of these turbidites is still not understood but earthquakes or tsunami waves associated with the mega scale traenadjupet slide and the storegga slide events are considered to be the most likely mechanism at least during the holocene interglacial period

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

eddy kinetic energy in the north atlantic from surface drifters one hundred ten satellite tracked freely drifting buoys measured velocities and trajectories of the near surface currents in the north atlantic mean velocity values and the velocity variance about the mean were calculated for different regions a horizontal map of eddy kinetic energy was prepared on a 2 2 grid between latitudes 20 and 55 n maximum eddy energy 3000 cm2 s 2 coincides with the high speed gulf stream jet where it begins large amplitude meanders near 37 n 67 w a tongue of high eddy energy coincides with the stream s path eastward and around the grand banks into the newfoundland basin where values of 1000 cm2 s 2 are found a weaker tongue extends eastward across the mid atlantic ridge near 45 n a second weak extension reaches southeastward from the stream and crosses the mid atlantic ridge between 30 and 35 n north and south of the stream eddy energy diminishes rapidly reaching an e folding at 300 km from the axis values of 200 cm2 s 2 were observed in the mid gyre region and 100 cm2 s 2 in the eastern north atlantic and north equatorial current although the gross distribution of eddy energy is similar to that determined from ship drift measurements there are significant differences eddy energy from drifters amounts to about twice the value measured by ship drift in the gulf stream and one half the ship drift values in the mid gyre it is suggested that these differences are due to the horizontal averaging of mesoscale motion and the errors in navigation both of which are problems with the ship drift technique

on the depth of oceanic earthquakes brief comments on the thermal structure of oceanic and continental lithosphere by mckenzie d jackson j and priestley k earth plan sci let 233 2005 337 349

source mechanisms of earthquakes near mid ocean ridges from body waveform inversion implications for the early evolution of oceanic lithosphere to investigate the early tectonic evolution of oceanic lithosphere we present a synthesis of the characteristics of near ridge earthquakes i e earthquakes which occur off the axis of major mid ocean spreading centers but in lithosphere less than 35 m y old near ridge seismicity for the past two decades has been rather evenly distributed along the major ridge systems with the exception of the central indian ocean and the eastern part of the cocos plate which have experienced a high rate of earthquake activity during that time for 32 near ridge earthquakes we determined the double couple orientation seismic moment centroid depth and source time function using a formal inversion technique based on matching synthetic and observed p and sh waveforms all types of faulting styles are observed seismogenic deformation in young oceanic lithosphere is concentrated in the first 15 m y and occurs almost entirely in the uppermost mantle from just below the moho to depths at which the temperature estimated from standard thermal models exceeds 800 c thrust faulting is not observed at depths greater than 10 km below the seafloor the deepest near ridge earthquakes are generally characterized by normal faulting focal mechanisms with the t axis oblique or perpendicular to the local spreading direction most of these earthquakes occur in the central indian ocean the transition from mechanisms characteristic of ridge axes to those characteristic of the near ridge environment occurs within the first few million years for lithosphere less than 35 m y old horizontal compressive stress associated with the cooling and subsidence of the lithosphere ridge push does not appear to be the dominant source of stress released in earthquakes this result may be used to place a lower bound of several hundred bars on the typical stress difference in young oceanic lithosphere this bound together with the observed depth of faulting implies that the strain rate associated with seismic deformation is locally at least 10 15 s 1 we propose that thermoelastic stresses associated with plate cooling play an important role in near ridge earthquakes this source of stress can account for the mechanisms and depths of many near ridge earthquakes and for the concentration of activity in very young lithosphere the comparative aseismicity of the oceanic crust may reflect the concentration of thermoelastic stress below the moho due to different material properties for the crust and upper mantle or the early release of thermoelastic stresses through hydrothermal circulation and cracking throughout the crust at or near the ridge axis the higher level of near ridge seismicity in the indian ocean may be the result of modification or enhancement of the more typical near ridge stress state by such local processes as the continental collision between india and asia or active secondary convection beneath the young lithosphere of the indian plate

barotropic instability in the west spitsbergen current 1 barotropic instability in the shoreward branch of the west spitsbergen current is investigated on the basis of data from an array of current meter moorings along 78 83 n across the upper continental slope and shelf break west of svalbard the slowly varying background current profile is modeled as an along slope asymmetric jet anchored to the shelf break numerical linear stability analyses are performed on the idealized current profile and topography revealing the characteristic period wavelength and growth rate of unstable vorticity waves detailed analysis of the ambient current profile in 2007 2008 shows that unstable conditions are present during 40 of the 10 month measurement record depending on the localization width and amplitude of the current jet the resulting vorticity waves are localized at the shelf break and are able to exchange water masses across the oceanic arctic front typical wavelengths and periods are 20 40 km and 40 70 h respectively wavelet coherence and complex demodulation analyses of the current meter data confirm that transient signals of similar periodicity as predicted by the stability analysis exist in the data record prominently during the winter and spring months estimates of the heat loss contribution from isopycnal diffusion reach 1 4 tw during the time intervals when unstable vorticity waves are active at the shelf break implying that the dynamics of the west spitsbergen current play a significant role in the cooling process of the atlantic water on the way to the arctic ocean this cooling corresponds to an along shelf cooling rate of 0 08 c per 100 km

breaking into the plate a 7 6 mw fracture zone earthquake adjacent to the central indian ridge 1 on 15 july 2003 an extremely large 7 6 mw strike slip earthquake initiated on or near the end of an active transform along the northern central indian ridge the event propagated away from the plate boundary along the typically inactive fracture zone with a sense of slip that opposes the active transform slip direction seismically and hydroacoustically determined aftershock locations delineate a 210 25 km long mainshock rupture the seismic moment and rupture dimensions imply a stress drop of 4 5 6 5 mpa and a mean slip of 3 0 0 5 m the largest aftershock 5 6 nw occurred on the active portion of a neighboring transform at a distance of 160 km where mainshock induced static stress changes are predicted to promote failure near axis fracture zone earthquakes may promote and inhibit ridge parallel diking along different spreading segments perhaps contributing to inter segment variability in the rate and asymmetry of spreading

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