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

stress strain paradox plate coupling and forearc seismicity at the cascadia and nankai subduction zones abstract in the continental forearcs of the cascadia and nankai subduction zones geodetic strain measurements indicate crustal contraction in the direction of plate convergence nearly margin normal but earthquake focal mechanisms and other stress indicators show maximum compression along strike margin parallel it is evident that the geodetic strain signals reflect the temporal fluctuations of elastic stress associated with subduction earthquake cycles not the absolute stresses the absolute margin normal stress is not only much less than the margin parallel stress but also no greater than the lithostatic value indicating a very weak subduction thrust fault weak subduction faults are also consistent with geothermal data which require very low frictional heating along the faults great subduction earthquakes occur at very low shear stresses and cause small perturbations to the forearc stress regime because these small elastic stress perturbations are relatively fast they give large strain rates that are detected by geodetic measurements the present nearly margin normal contraction in both places is due to the locking of the subduction fault and the consequent increase in elastic stress in the direction of plate convergence with the margin parallel compression being dominant the small increase in margin normal stress may change the forearc seismicity in cascadia from a mixture of thrust and strike slip types into mainly thrust before the next great subduction earthquake in nankai the change should be from strike slip to quiescence as observed in the nankai forearc prior to the 1944 1946 great subduction earthquakes

tectonic model explaining divergent contraction directions along the cascadia subduction margin washington differential motion across the central cascadia subduction boundary in washington results in a complex pattern of folds and faults within the shelf and onshore parts of the accretionary margin faults and folds above a coastal north northwest trending thrust system provide evidence of ongoing subduction related contraction south of this coastal thrust system many fold axes and thrust faults trend east northeast in the direction of convergence these structures are not consistent with a simple subduction system undergoing northeastward convergence this deformation adjacent to the boundary between the subduction complex and the siletz terrane may be driven by relative convergence between the northward translating siletz terrane and the subduction complex the regional pattern of modern uplift rates is consistent with ongoing north south contraction across this boundary and the north south compressional stress field in the area

iceland scotland overflow water transport variability through the charlie gibbs fracture zone and the impact of the north atlantic current the charlie gibbs fracture zone cgfz a deep and wide gap in the mid atlantic ridge near 52 n is a gateway between the eastern and western subpolar regions for the atlantic meridional overturning circulation amoc in 2010 2012 an eight mooring array of current meters and temperature salinity sensors was installed across the cgfz between 500 m and the sea floor to measure the mean transport of westward flowing iceland scotland overflow water isow and investigate the impact of the eastward flowing north atlantic current nac on isow transport variability the 22 month record mean isow transport through the cgfz 1 7 0 5 sv 95 confidence interval is 30 lower than the previously published estimate based on 13 months of current only measurements 2 4 sv 1 2 sv saunders 1994 the latter mean estimate may have been biased high due to the lack of continuous salinity measurements although the two estimates are not statistically different due to strong mesoscale variability in both data sets empirical orthogonal function analysis and maps of satellite derived absolute dynamic topography show that weak westward isow transport events and eastward reversals are caused by northward meanders of the nac with its deep reaching eastward velocities these results add to growing evidence that a significant fraction of isow exits the iceland basin by routes other than the cgfz

interannual variability of the altimetry derived eddy field and surface circulation in the extratropical north atlantic ocean in 1993 2001 abstract the distribution of surface eddy kinetic energy eke depicts main oceanic surface circulation features the interannual variability of eke and associated geostrophic velocity anomalies in the north atlantic ocean were analyzed to describe the variations in oceanic currents between 1993 and 2002 the sea level anomaly maps of the combined topex poseidon ers 1 2 and topex poseidon alone satellite altimetry data were used to derive eke the study focused on the areas of the gulf stream extension gs north atlantic current nac azores current ac and the northeastern rockall channel and iceland basin and northwestern irminger basin and labrador sea north atlantic the interannual variability of the altimetry derived eke field in the gs extension area reflected the meridional displacements of the gs core described in earlier studies the interannual change of eke in the ac was characterized by high values in 1993 95 followed by lower eke in subsequent years the interannual variability of

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

northwest basin and range tectonic deformation observed with the global positioning system 1999 2003 1 we use geodetic velocities obtained with the global positioning system gps to quantify tectonic deformation of the northwest basin and range province of the western united states the results are based on gps data collected in 1999 and 2003 across five new quasi linear networks in northern nevada northeast california and southeast oregon the velocities show 3 mm yr westward movement of northern nevada with respect to stable north america west of longitude 119 w the velocities increase and turn northwest parallel to sierra nevada great valley microplate motion and similar to velocities previously obtained to the south the observations are explained by a kinematic model with three domains that rotate around euler poles in eastern oregon and western idaho northeast california experiences internal dextral shear deformation 11 2 3 6 nstrain yr subparallel to pacific north america motion relative motions of the domains imply 2 5 mm yr approximately east west extension in northwest nevada and 1 4 mm yr approximately north south contraction near the california oregon border the northward decreasing approximately east west extension in northwest nevada is consistent with the northern termination of basin and range deformation faulting and characteristic topography no significant extension is detected in the oregon basin and range the oregon cascade arc moves north at 3 5 mm yr and is possibly influenced by the approximately eastward motion of the juan de fuca plate these results disagree with secular northwest trenchward motion of the oregon forearc inferred from paleomagnetic rotations south of latitude 43 however trenchward motion exists and is consistent with block rotations approximately east west basin and range extension and northwest sierra nevada translation

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

viscoelastic cycle model of interseismic deformation in the northwestern united states summary we apply a viscoelastic cycle model to a compilation of gps velocity fields in order to address the kinematics of deformation in the northwestern united states a viscoelastic cycle model accounts for time dependent deformation following large crustal earthquakes and is an alternative to block models for explaining the interseismic crustal velocity field building on the approach taken in pollitz et al we construct a deformation model for the entire western united states based on combined fault slip and distributed deformation and focus on the implications for the mendocino triple junction mtj cascadia megathrust and western washington we find significant partitioning between strike slip and dip slip motion near the mtj as the tectonic environment shifts from northwest directed shear along the san andreas fault system to east west convergence along the juan de fuca plate by better accounting for the budget of aseismic and seismic slip along the cascadia subduction interface in conjunction with an assumed rheology we revise a previous model of slip for the m 9 1700 cascadia earthquake in western washington we infer slip rates on a number of strike slip and dip slip faults that accommodate northward convergence of the oregon coast block and northwestward convergence of the juan de fuca plate lateral variations in first order mechanical properties e g mantle viscosity vertically averaged rigidity explain to a large extent crustal strain that cannot be rationalized with cyclic deformation on a laterally homogeneous viscoelastic structure our analysis also shows that present crustal deformation measurements particularly with the addition of the plate boundary observatory can constrain such lateral variations

a 1000 year record of centennial scale cyclical vegetation change from maar lake sanjiaolongwan in northeastern china abstract to examine possible relationships between regional changes in vegetation and climate and fluctuations in solar activity we obtained a high resolution 1000 year pollen record from the sanjiaolongwan maar lake sjml in northeastern china an age model was established using analyses of 210pb 137cs and ams 14c the pollen assemblages indicate that during the last millennium the vegetation of the study area was temperate coniferous and deciduous broadleaved mixed forest although pinus is the most abundant pollen type in the record various lines of evidence suggest that it is not especially temperature sensitive however the analysis of the changes in pollen assemblages over the past 1000 years and a comparison with pollen records from other lakes in the region indicate that the quercus frequencies can be used as a relatively sensitive temperature index for the study area several notable cold periods with lower quercus frequencies occurred at approximately 1200 ad 1410 ad 1580 ad 1770 ad and 1870 ad these centennial scale cold periods basically correspond to major minima in solar activity suggesting that variations in solar activity may have been an important driver of climate and vegetation change in the study area during the last millennium

year round measurements of the irminger current variability of a two core current system observed in 2014 2016 the irminger current ic flowing northeastward along the western flank of the reykjanes ridge is an important component in the overturning of the north atlantic subpolar gyre a 2 year 2014 2016 time series from moored observations shows that the ic consists of two highly variable current cores a subsampling experiment using an ocean reanalysis showed that this current s variability is adequately captured by the array the two current cores contribute nearly equally to the mean volume transport the total 2 year mean transport was found to be 10 6 sv with a standard deviation of daily monthly values of 9 2 sv 4 4 sv and a standard error of 1 4 sv mean heat and freshwater transport were 0 21 pw and 22 5 msv respectively sref 34 92 the volume transport is strongest in spring and the average over the first year 8 6 sv was lower than that of the second year 12 4 sv coinciding with an increase in the density gradient over the array in the second year the variability of the total transport is dominated by variations in the western core while the warmer saltier eastern core contributes more to the heat and negative freshwater transport during the two observed winters which were marked by exceptional deep convection in the central irminger sea mixed layer deepening down to 400 m depth and outcropping of the 27 7 kg m3 isopycnal were observed within the ic

observations of irminger sea anticyclonic eddies mesoscale anticyclonic eddies in the irminger sea are observed using a mooring and a glider between 2002 and 2009 the mooring observed 53 anticyclones using a kinematic model objective estimates of eddy length scales and velocity structure are made for 16 eddies anticyclones had a mean core diameter of 12 km and their mean peak observed azimuthal speed was 0 1 m s 1 they had core salinities and potential temperatures of 34 91 34 98 and 4 488 5 34 degrees c respectively making them warm and salty features these properties represent a typical salinity anomaly of 0 03 and a temperature anomaly of 0 28 degrees c from noneddy values all eddies had small 1 rossby numbers in 2006 the glider observed two anticyclones having diameters of about 20 km and peak azimuthal speeds of about 0 3 m s 1 similar salinity anomalies were detected throughout the irminger sea by floats profiling in anticyclones two formation regions for the eddies are identified one to the west of the reykjanes ridge and the other off the east greenland irminger current near cape farewell close to the mooring observations indicate that eddies formed in the former region are larger than eddies observed at the mooring a clear increase in eddy salinity is observed between 2002 and 2009 the observed breakup of these eddies in winter implies that they are a source of salt for the central gyre the anticyclones are similar to those found in both the labrador sea and norwegian sea making them a ubiquitous feature of the subpolar north atlantic basins

directly measured mid depth circulation in the northeastern north atlantic ocean the circulation of water masses in the northeastern north atlantic ocean has a strong influence on global climate owing to the northward transport of warm subtropical water to high latitudes but the ocean circulation at depths below the reach of satellite observations is difficult to measure and only recently have comprehensive direct observations of whole ocean basins been possible here we present quantitative maps of the absolute velocities at two levels in the northeastern north atlantic as obtained from acoustically tracked floats we find that most of the mean flow transported northward by the gulf stream system at the thermocline level about 600 m depth remains within the subpolar region and only relatively little enters the rockall trough or the nordic seas contrary to previous work our data indicate that warm saline water from the mediterranean sea reaches the high latitudes through a combination of narrow slope currents and mixing processes at both depths under investigation currents cross the mid atlantic ridge preferentially over deep gaps in the ridge demonstrating that sea floor topography can constrain even upper ocean circulation patterns

partitioning of sediment on the shelf offshore of the columbia river littoral cell this paper is not subject to u s copyright the definitive version was published in marine geology 273 2010 11 31 doi 10 1016 j margeo 2010 02 001

listric normal faulting on the cascadia continental margin analysis of multichannel seismic reflection profiles reveals that listric normal faulting is widespread on the northern oregon and washington continental shelf and upper slope suggesting e w extension in this region fault activity began in the late miocene and in some cases has continued into the holocene most listric faults sole out into a subhorizontal d6collement coincident with the upper contact of an eocene to middle miocene m61ange and broken formation mbf known as the hoh rock assemblage onshore whereas other faults penetrate and offset the top of the mbf the areal distribution of extensional faulting on the shelf and upper slope is similar to the subsurface distribution of the mbf evidence onshore and on the continental shelf suggests that the mbf is overpressured and mobile for listric faults which become subhorizontal at depth these elevated pore pressures may be sufficient to reduce effective stress and to allow downslope movement of the overlying stratigraphic section along a low angle 0 1o 2 5 o detachment coincident with the upper mbf contact mobilization extension and unconstrained westward movement of the mbf may also contribute to brittle extension of the overlying sediments no pliocene or quaternary extensional faults have been identified off the central oregon or northernmost washington coast where the shelf is underlain by the rigid basaltic basement of the siletzia terrane quaternary extension of the shelf and upper slope is contemporaneous with active accretion and thrust faulting on the lower slope suggesting that the shelf and upper slope are decoupled from subduction related compression

geodetic constraints on areal changes in the pacific north america plate boundary zone what controls basin and range extension using 1500 geodetic velocities we model the present day spatial patterns of areal changes inside the pacific north america plate boundary zone from this model we show that between the central gulf of california and the queen charlotte islands there is no significant net change in surface area this zero net areal change result allows us to relate regions of areal growth to areas of equivalent contraction elsewhere within the plate boundary zone we find that areal growth of the basin and range province brp and its eastern margin 5 2 0 1 10 3 m 2 yr is balanced by areal reduction near northwestern california between 38 n and 42 n the san andreas fault system south of 38 n and the plate boundary zone north of 42 n including the juan de fuca and gorda ridge systems each have no significant net areal change our results suggest a kinematic relationship between extension in the brp and contraction near the northern california coast ranges and klamath mountains from these observations we propose that although brp extension may be caused by internal forces the southernmost cascadia subduction zone provides a window of escape that acts as a stress guide to brp extension as well as northwestward sierra nevada motion such a dynamic model is consistent with independent findings that 1 the least principal horizontal stress orientations in the brp are toward northern california 2 extension directions in the brp have changed orientation to track the northward migration of the mendocino triple junction and 3 the southernmost cascadia subduction zone is a relatively weak plate boundary

subpolar mode water in the northeastern atlantic 1 averaged properties and mean circulation 1 subpolar mode waters spmw in the eastern north atlantic subpolar gyre are investigated with hydrographic and lagrangian data surface drifters and isopycnal floats historical hydrographic data show that spmws are surface water masses with nearly uniform properties confined between the ocean surface and the permanent pycnocline spmws represented by densities 27 3 27 4 and 27 5 are present in the eastern subpolar gyre and are influenced by the topography and the regional circulation construction of an absolute surface stream function from surface drifters shows that spmws are found along the mean path of each of the several branches of the north atlantic current nac and their density increases gradually downstream the rockall trough branch of the nac carries 27 3 27 4 and 27 5 spmw toward the iceland faroe front in the iceland basin the subarctic front along the western flank of the rockall plateau carries a similar sequence of spmw the western side of the central iceland basin branch of the nac on the other hand veers westward and joins the east reykjanes ridge current feeding the 27 5 spmw on the reykjanes ridge the separation among the various nac branches most likely explains the different properties that characterize the 27 5 spmw found on the reykjanes ridge and on the iceland faroe ridge since the branches of the nac have a dominant northeastward direction the newly observed distribution of spmw combined with the new stream function calculation modify the original hypothesis of mccartney and talley 1982 of a smooth cyclonic pathway for spmw advection and density increase around the subpolar gyre

upper plate contraction north of the migrating mendocino triple junction northern california implications for partitioning of strain geologic measurement of permanent contraction across the cascadia subduction margin constrains one component of the tectonic deformation along the convergent plate boundary the component critical for the seismic hazard assessment of crustal faults a comprehensive survey of active faults in onshore subduction margin rocks at the southern end of the cascadia subduction zone indicates that these thrust faults accommodate 10 mm yr of convergence oriented 020 045 seismotectonic models of subduction zones typically assign this upper plate strain to the estimate of aseismic slip on the megathrust geodetic models include this permanent crustal strain within estimates of elastic strain accumulation on the megathrust both types of models underestimate the seismic hazard associated with crustal faults subtracting the observed contraction from the plate convergence rate 40 50 mm yr directed 040 055 leaves 30 40 mm yr of convergence to be partitioned between slip on the megathrust contraction within the southern juan de fuca plate and crustal contraction outside the subduction complex rocks this simple estimate of slip partitioning neglects the discrepancy between the plate convergence and contraction directions in the vicinity of the mendocino triple junction the san andreas and cascadia limbs of the mendocino triple junction are not collinear the eastern edge of the broad san andreas boundary is 85 km east of the cascadia subduction boundary and across this zone the pacific plate converges directly with the north america plate the skewed orientation of crustal structures just north of the leading edge of the pacific plate suggests that they are deforming in a hybrid stress field resulting from both juan de fuca north america motion and pacific north america motion the composite convergence direction 50 mm yr directed 023 is consistent with the compressive stress axis 020 inferred from focal mechanisms of crustal earthquakes in the humboldt region deformation in such a hybrid stress field implies that the crustal faults are being loaded from two major tectonic sources the slip on crustal faults north of the mendocino triple junction may consume 4 5 mm yr of pacific humboldt convergence the remaining 17 18 mm yr of convergence may be consumed as distributed shortening expressed in the high rates of uplift in the cape mendocino region or as northward translation of the continental margin north of the triple junction

strong winter cooling over the irminger sea in winter 2014 2015 exceptional deep convection and the emergence of anomalously low sst deep convection is presumed to be vital for the north atlantic meridional overturning circulation even though observational evidence for the link remains inconclusive modeling studies have suggested thatconvection will weaken as a result of enhanced freshwater input the emergence of anomalously low seasurface temperature in the subpolar north atlantic has led to speculation that this process is already at work hereweshow that strong atmospheric forcing in the winter of 2014 2015 associated with a high north atlanticoscillation nao index produced record mixed layer depths in the irminger sea local mixing removed thestratification of the upper 1400mand ventilated the basin to middepths resembling a state similar to themid 1990s when a positive nao also prevailed we show that the strong local atmospheric forcing ispredominantly responsible for the negative sea surface temperature anomalies observed in the subpolar northatlantic in 2015 and that there is no evidence of permanently weakened deep convection

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

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

north atlantic ocean surface currents 1 close to 1800 surface drifters are used to investigate the 15 m circulation of the north atlantic ocean the data are used to describe structures of the average eulerian circulation and of the associated eddy variability the data resolve scales on the order of 50 km which have hitherto not been systematically described in particular near shelf breaks and near the most intense currents the gulf stream the north atlantic current nac and the frontal currents of the subpolar gyre this reveals a complex series of quasi permanent eddies meanders and recirculation patterns gulf stream intensity is portrayed as changing abruptly near 54 w east of which it is identified as two current branches centered near 39 and 41 5 n the northern one connecting more directly with the nac and the southern one with the recirculation gyre and the azores current ac many features of the currents are controlled by topography in particular currents are often intensified near shelf breaks or parallel to ridges in the subpolar gyre however the largest northward branch of the nac in the icelandic basin is located near the deepest bathymetry not near steep bathymetry other currents in particular in the subtropical gyre are less clearly related to topography for instance the ac is featured as a zonal eastward current extending far west of the mid atlantic ridge mar to at least 55 w and possibly 63 w in the interior and away from topographic features the eddy kinetic energy eke is the largest where the mean currents are the largest in the subpolar gyre there are striking differences in eke between southward flowing currents the labrador and east greenland current and the northward flowing currents west greenland current and branches of the nac which have higher eke the areas of weakest variability are located in the southwest part of the subpolar gyre northeast of iceland and in the eastern atlantic south of 45 n the ac eddies and the mesoscales south of the canary islands transect this eastern eddy desert drifter trajectories are used as realizations of lagrangian particles in the vicinity of current cores these illustrate the variety of paths or connections between different current systems and demonstrate cross stream dispersions

rapid freshening of the deep north atlantic ocean over the past four decades the overflow and descent of cold dense water from the sills of the denmark strait and the faroe shetland channel into the north atlantic ocean is the principal means of ventilating the deep oceans and is therefore a key element of the global thermohaline circulation most computer simulations of the ocean system in a climate with increasing atmospheric greenhouse gas concentrations predict a weakening thermohaline circulation in the north atlantic as the subpolar seas become fresher and warmer1 2 3 and it is assumed that this signal will be transferred to the deep ocean by the two overflows from observations it has not been possible to detect whether the ocean s overturning circulation is changing but recent evidence suggests that the transport over the sills may be slackening4 here we show through the analysis of long hydrographic records that the system of overflow and entrainment that ventilates the deep atlantic has steadily changed over the past four decades we find that these changes have already led to sustained and widespread freshening of the deep ocean

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

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

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

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

hydrographic changes in the labrador sea 1960 2005 abstract the labrador sea has exhibited significant temperature and salinity variations over the past five decades the whole basin was extremely warm and salty between the mid 1960s and early 1970s and fresh and cold between the late 1980s and mid 1990s the full column salinity change observed between these periods is equivalent to mixing a 6 m thick freshwater layer into the water column of the early 1970s the freshening and cooling trends reversed in 1994 starting a new phase of heat and salt accumulation in the labrador sea sustained throughout the subsequent years it took only a decade for the whole water column to lose most of its excessive freshwater reinstate stratification and accumulate enough salt and heat to approach its record high salt and heat contents observed between the late 1960s and the early 1970s if the recent tendencies persist the basin s storages of salt and heat will fairly soon likely by 2008 exceed their historic highs the main process responsible for the net cooling and freshening of the labrador sea between 1987 and 1994 was deep winter convection which during this period progressively developed to its record depths it was caused by the recurrence of severe winters during these years and in its turn produced the deepest densest and most voluminous labrador sea water lsw1987 1994 ever observed the estimated annual production of this water during the period of 1987 1994 is equivalent to the average volume flux of about 4 5 sv with some individual annual rates exceeding 7 0 sv once winter convection had lost its strength in the winter of 1994 1995 the deep lsw1987 1994 layer lost communication with the mixed layer above consequently losing its volume while gaining heat and salt from the intermediate waters outside the labrador sea while the 1000 2000 m layer was steadily becoming warmer and saltier between 1994 and 2005 the upper 1000 m layer experienced another episode of cooling caused by an abrupt increase in the air sea heat fluxes in the winter of 1999 2000 this change in the atmospheric forcing resulted in fairly intense convective mixing sufficient to produce a new prominent lsw class lsw2000 penetrating deeper than 1300 m this layer was steadily sinking or deepening over the years following its production and is presently overlain by even warmer and apparently less dense water mass implying that lsw2000 is likely to follow the fate of its deeper precursor lsw1987 1994 the increasing stratification of the intermediate layer implies intensification in the baroclinic component of the boundary currents around the mid depth perimeter of the labrador sea the near bottom waters originating from the denmark strait overflow exhibit strong interannual variability featuring distinct short term basin scale events or pulses of anomalously cold and fresh water separated by warm and salty overflow modifications regardless of their sign these anomalies pass through the abyss of the labrador sea first appearing at the greenland side and then about a year later at the labrador side and in the central labrador basin the northeast atlantic deep water 2500 3200 m originating from the iceland scotland overflow water reached its historically freshest state in the 2000 2001 period and has been steadily becoming saltier since then it is argued that lsw1987 1994 significantly contributed to the freshening density decrease and volume loss experienced by this water mass between the late 1960s and the mid 1990s via the increased entrainment of freshening lsw the hydrostatic adjustment to expanding lsw or both

origin formation and variability of the subpolar mode water located over the reykjanes ridge the origin and formation of the subpolar mode water spmw located over the reykjanes ridge in the north atlantic ocean and the variability of its properties over the period 1966 2004 are investigated through the use of a global eddy permitting 1 4 degrees ocean sea ice model and a lagrangian analysis tool the spmw is fed by subtropical and subpolar waters advected by the branches of the north atlantic current the spmw acquires its properties when its source waters enter the winter mixed layer in the iceland basin the spmw temperature variability is mainly explained by variations of the relative contributions of the subtropical and subpolar water transports to the total transport compared to the 1966 2004 mean lower higher subtropical water relative transport contribution leads to colder warmer spmw in the early 1990s in the late 1960s and late 1990s the intensity of the winter convection in the iceland basin also influences the spmw temperature through the amount of relatively cold intermediate waters of subtropical origin integrated in the spmw layer strong convection partly explains the cold spmw of the early 1990s the large increase in the spmw temperature in the late 1990s is due to both a decrease in the winter convection and an increase in the relative transport of the subtropical waters

a fluvial record of long term steady state uplift and erosion across the cascadia forearc high western washington state six late quaternary river terraces preserved along the clearwater river in northwestern washington state provide a 140 ka record of long term incision and uplift across the western side of the cascadia forearc high terrace ages are constrained by weathering rind and radiocarbon dating and by correlation to dated coastal glacio fluvial deposits and the global eustatic curve the terraces overlie flat bedrock surfaces called straths which represent uplifted segments of the river channel bedrock incision is measured by the height of a strath relative to the adjacent modern river channel the straths along the clearwater show an upstream increase in bedrock incision ranging from 0 at the coast to a maximum of 110 m in the headwaters the incision at any point along the profile increases systematically with strath age the calculated incision rates range from 10 ky the clearwater river valley has maintained a steady state profile defined by a long term balance in the rates of incision and rock uplift upstream divergence of terraces is best explained by an increase in the rate of rock uplift from the coast toward the central part of the range these results are consistent with other evidence indicating a long term steady state balance between the accretionary influx and the erosional outflux for this part of the cascadia subduction wedge since 14 ma these results help show how terrace deposits form in tectonically active landscapes the dominantly fluvial clearwater drainage was forming straths while alpine glaciers were advancing in adjacent drainages in turn the straths were buried during the transition to interglacial times because of increased sediment supply due to local deglaciation and because of eustatic highstands that forced aggradation in the lower reach of the drainage and across the continental shelf as well the fluvial system shows strong forcing by the glacial climate cycle even so the river appears to have returned to the same valley profile during each cycle of strath cutting thus bedrock incision is clearly unsteady at time scales shorter than the glacial climate cycle 100 ky but appears to be relatively steady when averaged over longer time scales a simple kinematic model is used to examine how uplift of the cl our analysis indicates that the accretionary flux into the wedge occurs mainly by frontal accretion and not by underplating if accretion occurred entirely at the front of the wedge the present west coast should be moving to the northeast at 3 m ky relative to a fixed puget sound this prediction is in good agreement with offset of a 122 ka sea cliff preserved at the southwest side of the clearwater valley profile in this case the long term margin perpendicular shortening would account for 20 to 35 percent of the geodetically measured northeast southwest shortening across the olympic mountains

gyre scale deep convection in the subpolar north atlantic ocean during winter 2014 2015 using argo floats we show that a major deep convective activity occurred simultaneously in the labrador sea lab south of cap farewell scf and the irminger sea irm during winter 2014 2015 convection was driven by exceptional heat loss to the atmosphere up to 50 higher than the climatological mean this is the first observation of deep convection over such a widespread area mixed layer depths exceptionally reached 1700 m in scf and 1400 m in irm the deep thermocline density gradient limited the mixed layer deepening in the labrador sea to 1800 m potential densities of deep waters were similar in the three basins 27 73 27 74 kg m 3 but warmer by 0 3 c and saltier by 0 04 in irm than in lab and scf meaning that each basin formed locally its own deep water the cold anomaly that developed recently in the north atlantic ocean favored and was enhanced by this exceptional convection

two years of observations of warm core anticyclones in the labrador sea and their seasonal cycle in heat and salt stratification abstractbetween 25 september 2007 and 28 september 2009 a heavily instrumented mooring was deployed in the labrador sea offshore of the location where warm core anticyclonic irminger rings are formed the 2 year time series offers insight into the vertical and horizontal structure of newly formed irminger rings and their heat and salt transport into the interior basin in 2 years 12 irminger rings passed by the mooring of these 11 had distinct properties while 1 anticyclone likely passed the mooring twice eddy radii 11 35 km were estimated using the dynamic height signal of the anticyclones 8 18 cm together with the observed velocities the anticyclones show a seasonal cycle in core properties when observed 1 9 c in temperature and 0 07 in salinity at middepth that has not been described before the temperature and salinity are highest in fall and lowest in spring cold fresh caps suggested to be an important source of freshwater were seen in spring but were almost nonexistent in fall th