arctic ocean deep water masses in the western iceland sea the icelandic danish contribution to the international greenland sea project was devoted to a study of the distribution and transport of water masses in the western iceland sea each year in september from 1987 to 1991 temperature and salinity were observed on a station net in the area off east greenland from the denmark strait in the south to 72 30 n the data reveal that the deep water column of the western iceland sea is occupied by a number of slightly different water masses which all can be traced back to a formation in the arctic ocean it is especially noticeable that in some years almost undiluted eurasian basin deep water can be observed as far south as the denmark strait

the tritium krypton 85 age of denmark strait overflow water and gibbs fracture zone water just south of denmark strait the opposite time trends of the input of tritium and 85kr to the surface ocean produce a tritium 85kr ratio for surface water that is a strong function of time and this ratio was used to determine the age of denmark strait overflow water dsow and gibbs fracture zone water gfzw just south of denmark strait dsow and gfzw were identified by their temperature salinity oxygen and silica characteristics in a section of stations 460 km south of denmark strait taken during the transient tracers in the ocean north atlantic study expedition in 1981 dsow was the densest water observed in the section and there were two types a low salinity type and a slightly higher salinity more dense type both types originated from arctic intermediate water aiw behind the greenland iceland ridge the tritium and 85kr data reveal that the low salinity type resided behind the greenland iceland ridge for about 1 year before flowing into the irminger sea compared to about 15 years for the higher salinity type the volume transport of the low salinity type of dsow was estimated to have a lower limit of 0 8 sv gfzw forms in the northeastern atlantic from a mixture of water flowing out of the norwegian sea at about 900 m depth and the northeastern atlantic water into which it flows about 70 of the tritium and 85kr burden of gfzw comes from northeastern atlantic water and 30 from norwegian sea water the age of gfzw just south of denmark strait relative to its formation in the northeastern atlantic is 7 5 4 6 5 years which corresponds to a mean current speed of 1 6 10 1 0 6 cm s

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

increasing amount of arctic ocean deep waters in the greenland sea 1 in the last three decades deep convection has come to a halt in the greenland sea hydrographic data reveal that during this period temperature and salinity in the deep greenland sea have increased at mean rates without precedent in the last 100 years and these trends are among the highest in the global deep ocean the origin of these changes is identified as the advection of arctic ocean deep waters and the necessary transports to explain them are calculated 0 44 0 09 sv despite the fact that the deep greenland sea hardly covers 0 05 of the global surface the resulting trends constitute 0 3 of the world ocean heat content increase per unit area of earth s surface and 0 1 of the global sea level rise these results suggest that changes of the deep arctic mediterranean and their contribution to the global budgets need to be addressed

the thermohaline circulation of the arctic ocean and the greenland sea the thermohaline circulation of the arctic ocean and the greenland sea is conditioned by the harsh high latitude climate and by bathymetry warm atlantic water loses its heat and also becomes less saline by added river run off in the arctic ocean this leads to rapid cooling of the surface water and to ice formation brine released by freezing increases the density of the surface layer but the ice cover also insulates the ocean and reduces heat loss this limits density increase and in the central arctic ocean a low salinity surface layer and a permanent ice cover are maintained only over the shallow shelves where the entire water column is cooled to freezing can dense water form and accumulate to eventually sink down the continental slope into the deep ocean the part of the atlantic water which enters the arctic ocean is thus separated into a low density surface layer and a denser deep circulation these two loops exit through fram strait the waters are partly rehomogenized in the greenland sea the main current is confined to the greenland continental slope but polar surface water and ice are injected into the central gyre and create a low density lid allowing for ice formation in winter this leads to a density increase sufficient to trigger convection upwelling and subsequent ice melt the convection maintains the weak stratification of the gyre and also reinforces the deep circulation loop as the transformed waters return to the north atlantic the low salinity upper water of the east greenland current enters the labrador sea and influences the formation of labrador sea deep water the dense loop passes through denmark strait and the faroe shetland channel and sinks to contribute to the north atlantic deep water changes in the forcing conditions might alter the relative strength of the two loops this could affect the oceanic thermohaline circulation on a global scale

the effect of arctic freshwater pathways on north atlantic convection and the atlantic meridional overturning circulation abstractthis study examines the relative roles of the arctic freshwater exported via different pathways on deep convection in the north atlantic and the atlantic meridional overturning circulation amoc deep water feeding the lower branch of the amoc is formed in several north atlantic marginal seas including the labrador sea irminger sea and the nordic seas where deep convection can potentially be inhibited by surface freshwater exported from the arctic the sensitivity of the amoc and north atlantic to two major freshwater pathways on either side of greenland is studied using numerical experiments freshwater export is rerouted in global coupled climate models by blocking and expanding the channels along the two routes the sensitivity experiments are performed in two sets of models cm2g and cm2m with different control simulation climatology for comparison freshwater via the route east of greenland is found to have a larger direct impact on labrador sea convection in response to the changes of

branching of atlantic water within the greenland spitsbergen passage an estimate of recirculation atlantic water aw supplies the largest source of heat mass and salt to the arctic ocean via fram strait greenland spitsbergen passage yet it represents only a fraction of the atlantic water that resides in the greenland iceland norwegian and barents seas this is a result of both the branching of the central core of aw along its northward flow and the modification of its t s signature through air sea ice interactions and internal mixing this paper addresses the quantitative analysis of the three dominant atlantic water cores within fram strait and north of 76 n using an 11 year 1977 to 1987 hydrographic database spatial variations of heat volume and salt along its flow path of some 600 km showed that the major core of atlantic water that directly enters the arctic ocean svalbard branch did not extend past 20 e of the 9719 km3 of atlantic water existing within the region one third resided within the svalbard branch the remainder 22 and 45 were held within the return atlantic current and the yermak branches respectively restricting the analysis to a southern limit of 79 n effectively removed the return atlantic current and showed a nearly equal split between the two remaining branches work completed by bourke et al 1988 indicated that the yermak branch is largely recirculated to the south if true this analysis supports rudels 1987 model estimate of a 50 recirculation of aw within this region

on the deep water flow through the faroe bank channel a substantial part of the norwegian sea deep water outflow into the north atlantic takes place via the faroe bank channel the deepest passage through the greenland scotland ridge in order to estimate this flux of cold low saline bottom water a field survey comprising hydrographie observations as well as current measurements was carried out in the channel during may 1983 transport calculations were undertaken for a total of four sets of observations and yielded values ranging from 1 5 to 1 9 sverdrup the outflow is most likely subjected to hydraulic control and consequently a simple model has been formulated in order to determine the maximum discharge through a rotating channel of parabolic cross section this geometry is well adapted to the topography of the faroe bank channel and the theoretically predicted magnitude of the transport was found to be in good agreement with the observations

time series of winter convection in the greenland sea 1 in spite of the lack of bottom reaching convection in the greenland sea since the 1980s convection continues to ventilate the greenland gyre down to intermediate depth the variability of this ventilation activity is determined here annually for eight winters according to a multiple criteria catalogue applied to annual summer conductivity temperature depth transects along 75 n the comparison of the ventilation depths with the meteorological forcing the ice cover and the stratification of the water column shows the decisive influence of the hydrographic structure in the upper and intermediate layers ice on the other hand is not necessary for convection to occur ice formation does not even lead to particularly deep convection a stability maximum which currently dominates the vertical structure of the water column at medium depth limits the ventilation depths effectively

thermohaline circulation in the arctic mediterranean seas the renewal of the deep north atlantic by the various overflows of the greenland scotland ridges is only one manifestation of the convective and mixing processes which occur in the various basins and shelf areas to the north the arctic ocean and the greenland iceland and norwegian seas collectively called the arctic mediterranean the traditional site of deep ventilation for these basins is the greenland sea but a growing body of evidence also points to the arctic ocean as a major source of deep water this deep water is relatively warm and saline and it appears to be a mixture of dense brine enriched shelf water with intermediate strata in the arctic ocean the deep water exits the arctic ocean along the greenland slope to mix with the greenland sea deep water conversely very cold low salinity deep water from the greenland sea enters the arctic ocean west of spitsbergen within the arctic ocean the lomonosov ridge excludes the greenland sea deep water from the canadian basin leaving the latter warm saline and rich in silica in general the entire deep water sphere of the arctic mediterranean is constrained by the greenland scotland ridges to circulate internally therefore it is certain of the intermediate waters formed in the greenland and iceland seas which ventilate the north atlantic these waters have a very short residence time in their formation areas and are therefore able to rapidly transmit surface induced signals into the deep north atlantic

observed mean sea level changes around the north sea coastline from 1800 to present this paper assesses historic changes in mean sea level around the coastline of the north sea one of the most densely populated coasts in the world typically such analyses have been conducted at a national level and detailed geographically wider analyses have not been undertaken for about 20 years we analyse long records up to 200 years from 30 tide gauge sites which are reasonably uniformly distributed along the coastline and 1 calculate relative sea level trends 2 examine the inter annual and decadal variations 3 estimate regional geocentric sometimes also referred to as absolute sea level rise throughout the 20th century and 4 assess the evidence for regional acceleration of sea level rise relative sea level changes are broadly consistent with known vertical land movement patterns the inter annual and decadal variability is partly coherent across the region but with some differences between the inner north sea and the english channel data sets from various sources are used to provide estimates of the geocentric sea level changes the long term geocentric mean sea level trend for the 1900 to 2011 period is estimated to be 1 5 0 1 mm yr for the entire north sea region the trend is slightly higher for the inner north sea i e 1 6 0 1 mm yr and smaller but not significantly different on the 95 confidence level for the english channel i e 1 2 0 1 mm yr the uncertainties in the estimates of vertical land movement rates are still large and the results from a broad range of approaches for determining these rates are not consistent periods of sea level rise acceleration are detected at different times throughout the last 200 years and are to some extent related to air pressure variations the recent rates of sea level rise i e over the last two to three decades are high compared to the long term average but are comparable to those which have been observed at other times in the late 19th and 20th century

changes in the properties and distribution of the intermediate and deep waters in the fram strait abstract the fram strait is the only deep connection between the arctic ocean and the nordic seas greenland iceland and norwegian seas with a sill depth of approximately 2600 m consequently observations from this area reflect changes in the deep waters of the arctic mediterranean possible changes in the properties and distribution of the intermediate and deep water masses passing through the fram strait have been studied for the period from 1982 to 2008 at a zonal section at 79 n with special emphasis on the period from 1997 to 2008 the temperature of the arctic intermediate water shows large interannual variability where the period from 2002 to 2004 was especially cold indicating a strong winter convection in the nordic seas prior to those years the deep water originating from the norwegian sea has become warmer by about 0 10 c during the study period the changes in the properties of the norwegian sea deep water are caused by changes in its composition i e an increasing fraction of the eurasian basin deep water and a decreasing fraction of the greenland sea deep water each year if this trend continues the norwegian sea deep water will have similar characteristics as the eurasian basin deep water in about 15 years a prominent feature seen in the s diagrams from the deep fram strait is the disappearance of water with the characteristics of greenland sea deep water this very cold water temperature below 1 1 c was not observed after 1997 and the minimum temperature in the strait increased by 0 24 c between 1982 and 2008 in the fram strait the fraction of intermediate waters has increased while the fraction of deep waters from the nordic seas has decreased the fraction of deep waters originating from the arctic ocean shows no trend

a greenland sea perspective on the dynamics of postconvective eddies open ocean deep postconvection contributes to the formation of the dense waters that fill the global deep ocean the dynamics of postconvective vortices are key to understanding the role of convection in ocean circulation submesoscale coherent vortices scvs observed in convective regions are likely to be the anticyclonic components of hetons hetons are dipoles consisting of a surface cyclone and a weakly stratified subsurface anticyclone that can be formed by convection here key postconvective processes are investigated using numerical experiments of increasing sophistication with two primary goals 1 to understand how the ambient hydrography and topography influence the propagation of hetons and 2 to provide a theoretical context for recent observations of scvs in the greenland sea it is found that the alignment of hetons is controlled by ambient horizontal density gradients and that hetons self propagate into lighter waters as a result this provides a mechanism for transporting convected water out of a cyclonic gyre but the propagation is arrested if the heton meets large amplitude topography upon interaction with topography hetons usually separate and the surface cyclone returns toward denser water the anticyclone usually remains close to topography and may become trapped for several hundred days these findings may explain the observed accumulation and longevity of scvs at the greenland fracture zone on the rim of the greenland sea gyre the separation and sorting of cyclones from anticyclones have likely implications for the density and vorticity budgets of convective regions

fram strait and greenland sea transports water masses and water mass transformations 1999 2010 and beyond the exchanges between the nordic seas and the arctic ocean are important for the ocean circulation and climate transports are here estimated using summer hydrographic data from the greenland sea and the fram strait geostrophic transports are computed from hydrographic sections at 75 n in the greenland sea and at about 79 n in the fram strait geostrophic velocities are adjusted with summer velocities derived from argo floats and four conservation constraints are applied to a box closed by the two sections the estimated net volume transports are 0 8 1 5 sv southward net freshwater transports through the greenland sea section are estimated at 54 20 msv and through the fram strait section at 66 9 msv heat loss in the area between the two sections is estimated at 9 12 tw convection depths in the greenland sea are estimated from observations and vary between about 200 and 2000 dbar showing no trend water mass properties in the greenland sea are affected both by convection and lateral mixing vertical mixing is estimated from hydrography and based on it about 1 sv of diluted arctic ocean waters are estimated to enter the greenland sea the properties of atlantic intermediate and deep waters are studied deep water properties are defined using water mass triangles and are subject to decadal changes

absolute transport estimates of total and individual water masses in the northern greenland sea derived from hydrographic and acoustic doppler current profiler measurements 1 conductivity temperature depth transects across the greenland sea and fram strait provide geostrophic shear velocity profiles which were absolutely referenced using the simultaneous measurements from a vessel mounted acoustic doppler current profiler the measurements are performed mainly in 1997 with supplements in 1998 1995 and 1994 the observations confirm that all currents within the area have a strong barotropic component so that calculations based on the geostrophic method underestimate the transports considerably particulars for the transports of mass and heat are given for all individual and total water masses in the area meanders and eddies on horizontal scales between 20 and 70 km affect the total transport in the west spitsbergen current significantly the atlantic water transports range between 2 and 7 sv mainly dominated by the cross sectional area occupied by this water mass the total northward heat transport across 75 n is estimated as 54 7 tw and across 79 40 n as 42 tw in september 1997

the westward turning branch of the west spitsbergen current a salinity temperature survey of fram strait in september 1985 extending to north of 81 n demonstrated the western branch of the west spitsbergen current flowing northwest and then west mainly south of 81 n there also was a southwestward recirculation from the eastern branch of the west spitsbergen current baroclinic flow of warm water northward through 81 n was negligible or zero some doubt is cast on past flow diagrams based on core analysis which show the western branch of the west spitsbergen current coursing northward to 83 n one of a probable line of mesoscale eddies is described in some detail

the origin of norwegian sea deep water a nearly homogeneous water mass the norwegian sea deep water is found below 2000 m depth in the norwegian and lofoten basins of the norwegian sea recent observations indicate that this water is a mixture of relatively cold and fresh greenland sea deep water with warmer saltier eurasian basin deep water from the arctic ocean we have found this mixture along the western and southern periphery of the greenland sea near the level where the pressure compensated densities of the parent water masses are equal the along isopycnal mixing produces a remarkably uniform water mass which can be traced only a short distance away from its entry into the norwegian sea through gaps in the mid ocean ridge north of jan mayen island direct measurements of flow through these gaps confirm motion in the proper sense to accomplish this connection

the kinematics of a midlatitude continental mesoscale convective system and its mesoscale vortex the authors present a unique scale discriminating study of the environment relative circulations within a mesoscale convective system mcs and mesoscale convective vortex mcv the mcs a leading convective line and trailing stratiform region that became asymmetric passed through the national oceanic and atmospheric administration noaa profiler network npn in kansas and oklahoma on 1 august 1996 the mcv appeared in the mcs s stratiform region just prior to the system s mature stage and grew to a depth of over 12 km as the mcs dissipated the mcv did not apparently survive to the next day a spatial bandpass filter was used to divide observed wind into a component that was predominantly synoptic background wind and a component that was predominantly a mesoscale perturbation on that background wind a mesoscale updraft mesoscale downdraft and divergent outflows in the lower and upper troposphere were evident after the synoptic background wind was removed so these four circulations were internal and fundamental to the mcs the mesoscale perturbation in wind in the middle troposphere extended farther behind the mcs than ahead of it consistent with analytic studies and numerical simulations of gravity waves generated by heat sources characteristic of mcss with leading convective lines and trailing stratiform regions deepening of the mcv appeared to be reflected in the vertical wind shear at the vortex s center as the mcv strengthened the mesoscale shear through its lower part decreased perhaps as wind became more vortical at increasing altitudes mesoscale and synoptic vertical shears were of similar magnitude so an average of environmental soundings outside an mcs probably does not accurately represent the shear that affects an mcv this suggests the need to reevaluate how the kinematical settings of mcvs are diagnosed

freshwater fluxes in the east greenland current a decade of observations 1 over a decade of mooring measurements in the western fram strait at 78 50 n shows that the annual mean liquid freshwater flux fwf in the east greenland current is relatively constant at 1274 453 km3 yr 1 40 4 14 4 msv despite the fact that the annual mean total volume transport of the egc has more than doubled since 2001 this is shown to be due to an increase of the transport in the deeper ocean and the fact that the largest fw content is present on the east greenland shelf and not in the core of the egc in order to capture the fwf on the shelf modeling results of naosim are included showing that a mean contribution of fwf on the shelf of at least 807 357 km3 yr 1 25 6 11 3 msv should be added to the fwf obtained for the egc when compared to the extra input of freshwater required to account for the 1960 1990 freshening of the northern north atlantic the observed variations in the 1998 2008 egc liquid freshwater fluxes are small

a new path for the denmark strait overflow water from the iceland sea to denmark strait 1 denmark strait overflow water dsow is one of the main components of the thermohaline circulation there has been no consensus on where it is formed and by which way it is brought to the denmark strait it is shown here that it is brought to the sill by a hitherto unknown current that is traced from the sill back into the iceland sea north of iceland the transport of this current is sufficient to account for a major part of the transport of dsow as it has been measured at the sill if some entrainment of ambient water is assumed this supports theories suggesting that the iceland sea is the main source for the dsow and this has consequences for the way in which climate change affects the thermohaline circulation

long lived vortices as a mode of deep ventilation in the greenland sea the greenland sea is one of a few sites in the world ocean where convection to great depths occurs1 2 3 4 a process that forms some of the densest waters in the ocean but the role of deep convective eddies which result from surface cooling and mixing across density surfaces followed by geostrophic adjustment5 has not been fully taken into account in the description of the initiation and growth of convection6 here we present tracer float and hydrographic observations of long lived 1 year and compact 5 km core diameter vortices that reach down to depths of 2 km the eddies form in winter near the rim of the greenland sea central gyre and rotate clockwise with periods of a few days the cores of the observed eddies are constituted from a mixture of modified atlantic water that is warm and salty with polar water that is cold and fresh we infer that these submesoscale coherent eddies contribute substantially to the input of atlantic and polar waters to depths greater than 500 m in the central greenland sea

deep water formation and exchange rates in the greenland norwegian seas and the eurasian basin of the arctic ocean derived from tracer balances abstract multi tracer data sets collected in the greenland norwegian seas and the eurasian basin of the arctic ocean in the 1970s and 1980s are used together with temperature and salinity to 1 constrain box model calculations of the deep water formation rates in the greenland sea and the eurasian basin of the arctic ocean and 2 estimate the exchange rates of deep waters depth 1 500m between the greenland norwegian seas and the eurasian basin we obtain deep water formation rates of 0 1sv since 1980 to 0 47sv from at least 1965 to 1980 for the greenland sea and 0 3sv for the eurasian basin of the arctic ocean the southward flux of eurasian basin deep water through fram strait is estimated to be about 1sv about 0 12sv of this flux are transported into the greenland sea about 0 37sv reach the deep norwegian sea through the jan mayen fracture zone and about 0 39sv leave the arctic ocean through a shallower core which more or less directly feeds into the iceland sea and after modification eventually ends up in the overflow waters the outflow of eurasian basin deep water is balanced by deep water formation in the arctic ocean and by inflow of norwegian sea deep water about 0 77sv of deep water formed in the greenland sea and the eurasian basin contribute to the formation of north atlantic deep water uncertainties of the fluxes are estimated to be roughly 20 to 30

hydrographic observations in denmark strait in fall 1997 and their implications for the entrainment into the overflow plume denmark strait is the most important exit for water masses formed in the arctic mediterranean sea and supplies a substantial fraction of the north atlantic deep water observations obtained from rv aranda in august september 1997 indicate that the water crossing the 620m deep sill is mainly drawn from the intermediate waters of the east greenland current the overflow plume was stratified and capped by a less saline layer as it descended beyond 2000m the presence of a low salinity lid implies that entrainment of ambient water is small and that the downstream evolution of the plume characteristics is due to mixing within the plume between the initial overflow waters low salinity but dense water from the east greenland current flowing over the shelf may cross the shelf break south of the sill and add a less dense fraction to the overflow