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

impact of eastern arctic shelf waters on the nansen basin intermediate layers the eurasian shelves supply water to the nansen basin intermediate layers in two ways as buoyancy driven plumes of dense winter water and as permanent inflow of the barents sea branch of atlantic water while the plumes are local and seasonal phenomena the barents sea flow is part of the large scale circulation both interact with atlantic water which enters the arctic ocean through fram strait and moves as a subsurface boundary current eastward along the continental slope during the polarstern cruise ark ix 4 in summer 1993 the fram strait branch was observed as a narrow core within tens of kilometers of the barents sea shelf edge here several patches of cold low salinity water spread across the slope down to about 500 m depth their origin is assumed to be the northern barents sea they mix with the warm saline fram strait branch water fsbw so that the core properties of the latter become modified downstream in the eastern nansen basin the fram strait branch is displaced toward the inner basin by inflow of the barents sea branch of atlantic water bsbw this inflow appears as a broad 200 km wedge extending from 200 to 1300 m depth bsbw is colder and less saline than water of the fram strait branch and it is less dense and less stratified than the ambient water both branches appear to undergo vigorous mixing while spreading eastward so that any eastward continuation of the boundary flow transports about 50 bsbw and 50 fsbw above 600 m and about 80 bsbw and 20 fsbw below that level toward the canadian basin according to available observations the barents and kara seas are the only source areas for shelf waters ventilating the nansen basin below the halocline and these waters constitute a freshwater input rather than a salt input winter shelf water from the laptev sea cannot contribute to layers deeper than the upper halocline

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

holocene paleoceanography of the northwest passage canadian arctic archipelago abstract a series of cores box and piston were collected at 2 key locations in lancaster sound cores 2004 804 009 bc and pc and barrow strait cores 2005 804 004 bc and pc in the canadian arctic archipelago to document the evolution of sea surface conditions in the main axis of the northwest passage during the holocene time period reconstruction of sea surface parameters summer temperature and salinity duration of sea ice cover were estimated based on transfer functions using dinoflagellate cyst assemblages as proxy indicators the chronology of these cores is based on calibrated ams 14c dates 210pb analyses and correlations between paleomagnetic secular variations of the geomagnetic field and a predicted spherical harmonic model of the geomagnetic field cals7 k 2 our age models for both cores indicate that 009 pc spans the last 11 100 cal bp while 004 pc encompasses the last 10 800 cal bp calculated sedimentation rates are in the range of 43 140 cm kyr for core 009 pc and 15 118 cm kyr for core 004 pc allowing for a millennial time scale resolution in each core our results indicate relatively harsh conditions in lancaster sound between 10 800 and 9000 cal bp summer temperatures 2 c cooler than at present which we associate with the presence of active ice streams in northernmost baffin bay and a weak west greenland current this is followed by a warming trend up to 3 c higher than present that took place between 8500 and 5500 cal bp which we associate with the holocene thermal maximum and to a large scale atmospheric pattern such as the arctic oscillation operating at the millennial time scale this is concomitant with an increase in the relative abundance of phototrophic dinoflagellate cyst taxa a gradual cooling of sea surface temperature and increased sea ice follow this from 5500 cal bp until the modern period in barrow strait harsh sea surface conditions prevailed from 11 100 to 5500 cal bp with summer temperatures as low as 4 c cooler than at present the warming trend occurred later in this region between 5500 and 1000 cal bp after which a gradual cooling is observed until the modern period the apparent shift or opposite warming trends between lancaster sound and barrow strait after 5500 cal bp could be the result of a change in atmospheric circulation patterns related to a possible shift in the ao mode from ao to ao comparison of ice core 18o record from devon island ice cap and the reconstructed sea surface temperature from core 009 pc suggests a strong atmospheric oceanic coupling throughout the holocene in this area

neodymium isotopes in seawater from the barents sea and fram strait arctic atlantic gateways abstract the neodymium concentration c nd and isotopic composition e nd in seawater have been determined in the water column at five sites in the barents sea fram strait area where most of the water exchange between the arctic ocean and the north atlantic takes place in the main arctic ocean inflow branch across the barents sea the concentration and isotopic composition c nd 15 5 pmol kg and e nd 10 8 are similar to those reported for the northeastern nordic seas which is consistent with this region being a source area for the arctic inflow due to the addition of nd from svalbard shelf sediments the c nd in the surface waters above 150 m in the fram strait inflow branch is higher by a factor of 2 and the e nd is shifted to lower values 11 8 in the stratified nansen basin where cold low salinity water overlies warmer atlantic water the c nd and e nd do not vary with the vertical temperature salinity structure but are essentially constant and similar to those of the atlantic inflow throughout the entire water column down to 3700 m depth which indicates that the nd is to a large extent of atlantic origin compared to the atlantic inflow water the nd in the major arctic ocean outflow the fram strait show higher c nd in the surface waters above 150 m and a higher e nd 9 8 throughout the entire water column down to 1300 m depth sources for the more radiogenic nd isotopic composition in deep water of the fram strait outflow most likely involve boundary exchange with sediments on the shelf and slope as the water passes along the canadian archipelago river water is a possible source in the surface water but it also seems likely that pacific water nd modified by interactions on the shelf is an important component in the fram strait surface outflow changes in the relative proportions of inflow of river water and flow of pacific water through the arctic ocean could thus influence the isotopic composition of nd in the north atlantic

the arctic atlantic thermohaline circulation abstractthe atlantic ocean s thermohaline circulation is an important modulator of global climate its northern branch extends through the nordic seas to the cold arctic a region that appears to be particularly influenced by climate change a thermohaline circulation is fundamentally concerned with two degrees of freedom this is in particular the case for the inflow of warm and saline atlantic water through the nordic seas toward the arctic that is balanced by two branches of outflow the authors present an analytical model rooted in observations that constrains the strength and structure of this arctic atlantic thermohaline circulation it is found maybe surprisingly that the strength of atlantic inflow is relatively insensitive to anomalous freshwater input it mainly reflects changes in northern heat loss freshwater anomalies are predominantly balanced by the inflow s partition into estuarine and overturning circulation with southward polar outflow in the surface and dense overflow at depth res

evidence for warming of atlantic water in the southern canadian basin of the arctic ocean results from the larsen 93 expedition potential temperature and salinity s data obtained along the perimeter of the southern canadian basin north of the east siberian sea in 1993 aboard the ccgs henry larsen show higher temperatures in waters of atlantic origin than in available climatological data for the canadian basin in particular a front is observed near the mendeleyev ridge which separates the cooler atlantic waters of the canada basin from the warmer atlantic waters observed in the makarov basin the front is further characterized by a change in the s slope of arctic thermocline water and by thermohaline intrusions and s reversals within the atlantic layer the idea that this warm variety of atlantic water has come recently from the eurasian basin is supported by its higher level of the tracer cfc 11

water mass transformation in the barents sea inferred from radiogenic neodymium isotopes rare earth elements and stable oxygen isotopes abstract nearly half the inflow of warm and saline atlantic water aw to the arctic ocean is substantially cooled and freshened in the barents sea which is therefore considered a key region for water mass transformation in the arctic mediterranean am numerous studies have focused on this transformation and the increasing influence of aw on arctic climate and biodiversity yet geochemical investigations of these processes have been scarce using the first comprehensive data set of the distributions of dissolved radiogenic neodymium nd isotopes expressed as nd rare earth elements ree and stable oxygen isotope 18o compositions from this region we are able to constrain the transport and transformation of aw in the barents sea and to investigate which processes change the chemical composition of the water masses beyond what is expected from circulation and mixing inflowing aw and norwegian coastal water ncw both exhibit distinctly unradiogenic nd signatures of 12 4 and 14 5 respectively whereas cold and dense polar water pw has considerably more radiogenic nd signatures reaching up to 8 1 locally formed barents sea atlantic water bsaw and barents sea arctic atlantic water bsaaw are encountered in the northeastern barents sea and have intermediate nd values resulting from admixture of pw containing small amounts of riverine freshwater from the ob this article is part of a special issue entitled cycles of trace elements and isotopes in the ocean geotraces and beyond edited by tim m conway tristan horner yves plancherel and aridane g gonzalez

hydrothermal venting in magma deserts the ultraslow spreading gakkel and southwest indian ridges 1 detailed hydrothermal surveys over ridges with spreading rates of 50 150 mm yr have found a linear relation between spreading rate and the spatial frequency of hydrothermal venting but the validity of this relation at slow and ultraslow ridges is unproved here we compare hydrothermal plume surveys along three sections of the gakkel ridge arctic ocean and the southwest indian ridge swir to determine if hydrothermal activity is similarly distributed among these ultraslow ridge sections and if these distributions follow the hypothesized linear trend derived from surveys along fast ridges along the gakkel ridge most apparent vent sites occur on volcanic highs and the extraordinarily weak vertical density gradient of the deep arctic permits plumes to rise above the axial bathymetry individual plumes can thus be extensively dispersed along axis to distances 200 km and 75 of the total axial length surveyed is overlain by plumes detailed mapping of these plumes points to only 9 10 active sites in 850 km however yielding a site frequency fs sites 100 km of ridge length of 1 1 1 2 plumes detected along the swir are considerably less extensive for two reasons an apparent paucity of active vent fields on volcanic highs and a normal deep ocean density gradient that prevents extended plume rise along a western swir section 10 23 e we identify 3 8 sites so fs 0 3 0 8 along a previously surveyed 440 km section of the eastern swir 58 66 e 6 sites yield fs 1 3 plotting spreading rate us versus fs the ultraslow ridges and eight other ridge sections spanning the global range of spreading rate establish a robust linear trend fs 0 98 0 015us implying that the long term heat supply is the first order control on the global distribution of hydrothermal activity normalizing fs to the delivery rate of basaltic magma suggests that ultraslow ridges are several times more efficient than faster spreading ridges in supporting active vent fields this increased efficiency could derive from some combination of three dimensional magma focusing at volcanic centers deep mining of heat from gabbroic intrusions and direct cooling of the upper mantle and nonmagmatic heat supplied by exothermic serpentinization

formation of denmark strait overflow water by mixing in the east greenland current abstract hydrographic data and current meter records from the east greenland current collected during theperiod 1987 to 1989 around the latitude of the central greenland sea reveal the formation of a watermass having the characteristics of denmark strait overflow water dsow the downstream southwestward transport of this newly formed water mass can be substantial amounting to roughly halfof the outflow of dsow through denmark strait as reported in the literature the formation of dsow inthe east greenland current results from isopycnic mixing of recirculated atlantic water and upper arcticintermediate water substantial formation occurs when the neccessary conditions for baroclinic instabilityare satisfied and the current variability due to mesoscale eddies is high this is subject to significantchanges from year to year

mixing in the west spitsbergen current abstract twenty eight profiles of temperature and salinity down to 1 km depth have been measured in the area north from the coast of svalbard to latitude 84 40 n between 0 and 32 e longitude they show atlantic waters of the west spitsbergen current entering the arctic ocean in a bifilimentary mode one filament following the coastline and the other 300 km farther north apparently following the continental shelf break the profiles show these filaments mixing into the ambient water in a series of intrusive layers which are remarkably uniform over distances of hundreds of kilometers a triple peak structure at the atlantic water maximum is the dominant oceanographic characteristic of the area with salt fingering occurring on the upper surface of the cold intrusions and indications of double diffusive exchanges through the lower surface a system or eddies or meanders is postulated as the mechanism for the production of multiple fronts allowing the intrusive layers to extend to distances much greater t

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

greenland sea convection in the winter of 1987 1988 during february 1988 a layer of almost uniform temperature and salinity between 100 and 1250 m depth was observed in the central greenland sea this feature indicative of previous deep convection is explained in terms of a conceptual penetrative convection model

gravity field over singhbhum its relationship to geology and tectonic history abstract the gravity field over singhbhum and adjoining areas lying between latitude 21 to 23 15 n and longitude 84 to 87 30 e has been analysed the region has a very complex precambrian history dating as far back as 3200 m y and extending up to 850 m y during which time it experienced a number of orogenic cycles the activity has left an imprint on the gravity field which is marked by prominent gravity highs and lows the highs are invariably surrounding the singhbhum granite batholith whereas the lows are conspicuous over the granites and their margins the regional gravity field has been removed using a 4th order polynomial surface the residual anomalies over prominent highs and lows have been interpreted using two dimensional and three dimensional models for underlying rock formations it is inferred that the gravity highs are generally related to synclinal structures filled with sedimentary or metasedimentary formations and volcanics such as the iron ore group the singhbhum group dhanjori and simlipal basins the gravity lows can be attributed to a considerable thickness of granites of varying density which could have been formed during different metamorphic orogenic cycles by melting of a preexisting sialic crust

gravity field and deep structure of the bengal fan and its surrounding continental margins northeast indian ocean abstract a revised gravity anomaly map for the northeast indian ocean shows that the shelf edge underlying the eastern continental margin of india is a rather narrow but extensively linear gravity low minimum free air 149 mgal the bengal fan seaward of the shelf has a depressed gravity field average free air 20 to 30 mgal in spite of the enormous thickness of sediments of as much as 10 15 km the two buried ridges below the bengal fan the 85 east and 90 east ridges have a large negative 75 mgal and a substantial positive 40 mgal free air anomaly respectively the andaman and burmese arcs lying along the east margin of the bengal fan are active subduction areas which have typical bipolar gravity signatures with a maximum amplitude of 300 mgal gravity interpretation for three regional traverses across the central and northern parts of the bengal fan and their surrounding continental margins suggests that a thickened oceanic crustal wedge juxtaposes the transitional crust under the eastern continental slope of india the 85 east ridge that was created when the indian ocean lithosphere was very juvenile appears to underlie a nearly 10 km thick and 120 km wide oceanic crustal block consisting of the ridge material embedded in the upper lithosphere while the 90 east ridge submarine topography buried load below the bengal fan is probably isostatically compensated by a low density mass acting as a cushion at the base of the crust the bengal fan crust with its thick sediment layer is carried down the andaman subduction zone to a depth of about 27 km where possibly phase transition takes place under higher pressure the maximum sediment thickness at the andaman burmese subduction zone is of the order of 10 12 km the gravity model predicts a low density zone about 60 km wide below the andaman burmese volcanic arc penetrating from crustal to subcrustal depths in the overriding burma plate a more complex density distribution is however envisaged for the andaman volcanic arc that is split by the neogene back arc spreading ridge the ocean continent crustal transition possibly occurs farther east of the volcanic arc below the shan plateau margin in burma or below the mergui terrace at the malayan continental margin east of the andaman sea

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

an analysis of the gravity field and tectonic evaluation of the northwestern part of bangladesh abstract the total bouguer anomaly values of the northwestern part of bangladesh have been analysed on the basis of the trend shape and magnitude of the anomaly values residual gravity and the second vertical derivatives of gravity show only two near surface features viz the nilphamari and rangpur highs geological models of the two highs have been constructed on the basis of gravity modelling gravity data in conjunction with aeromagnetic and bore hole data enable us to propose four tectonic elements of the northwestern part of bangladesh the northern slope of the platform the stable platform the nawabganj gaibandha intracratonic high and the southern part of the platform

physical and geochemical properties across the atlantic pacific water mass front in the southern canadian basin temperature salinity nutrients oxygen and halocarbon data collected in the arctic ocean reveal a frontal structure previously unrecognized in the hydrography of the canadian basin samples were collected on a 1300 km section extending from the beaufort sea in the canada basin to the east siberian sea in the makarov basin these data collected in 1993 aboard the ccgs henry larsen reveal a lateral boundary between water masses of atlantic and pacific origin the term water mass assembly is introduced to describe the basic arrangement or vertical stacking of water masses found in the arctic ocean recognizing that water mass components within each assembly may differ from basin to basin using historical data two primary water mass assemblies are defined each consisting of three layers an upper layer an atlantic layer and a deep layer these two assemblies are marked by important differences one assembly here defined as the western arctic wa assembly is characterized by an upper layer of relatively fresh high nutrient water of pacific origin below this by an atlantic layer with a core temperature generally below 0 5 c and finally by a deep layer of higher salinities and colder temperatures about 0 5 c than found in the overlying atlantic layer the second assembly here defined as eastern arctic ea assembly is characterized by the absence of pacific water in the upper layer below this by an atlantic layer core as warm as 2 to 3 c and by a colder about 0 9 c deep layer because the presence or absence of pacific origin water is a key characteristic distinguishing the two assemblies we will refer to the water mass boundary between the two assemblies as the atlantic pacific front earlier research indicated that water masses in the arctic ocean were separated by a front above the lomonosov ridge into the canadian and eurasian basins although all larsen 93 stations from the canada basin a1 d1 display classic wa assembly characteristics the makarov basin station e1 shows ea assembly characteristics in the upper and atlantic layers and a wa assembly deep layer this suggests a relocation in the position of the atlantic pacific boundary away from the lomonosov ridge further larsen 93 data show the transition region between the atlantic and deep layers is fresher in the makarov basin than corresponding water in either the canada or eurasian basins implying a source of cold low salinity water perhaps from the laptev and east siberian shelves the front separating these two assemblies lies above the mendeleyev ridge and is marked by large lateral gradients in all measured properties in particular the penetration of anthropogenic halocarbons is 2 to 3 times deeper in the makarov basin than in the canada basin implying enhanced rates of ventilation this suggests that direct exchange between the canadian and eurasian basins has occurred recently near the perimeter and that physical and chemical properties including contaminants may have been transported by boundary currents more quickly from one basin to the other

duplex and along strike structural variation a case study from sikkim himalayan fold thrust belt abstract the sikkim lesser himalayan fold thrust belt records along strike structural variations over 15 km the lower lesser himalayan rangit duplex lhd is blind and the overlying pelling and ramgarh thrust sheets are more intensely folded and preserved in eastern sikkim than in western sikkim a retrodeformable regional balanced cross section reveals a minimum shortening of 403 km 80 with an average long term shortening rate of 18 mm yr in the eastern transect comparison with published data indicates that eastern sikkim records 47 km lesser shortening in western sikkim an 2 km high footwall main himalayan thrust mht ramp below the rangit duplex caused higher structural culmination exposing the duplex in contrast an 0 35 km high ramp below the rangit duplex in eastern sikkim did not create sufficient culmination to expose the duplex causing along strike discontinuous duplex exposure the lhd with a blind component and having fewer 11 but gentler dipping 40 horses transferred more displacement to the roof thrust in eastern sikkim than the twelve steeper dipping 60 horses in western sikkim lateral variations in location and height of footwall mht ramp initial width of the lesser himalayan basin and presence of a lateral ramp explain the structural variation in sikkim

changes in temperature and tracer distributions within the arctic ocean results from the 1994 arctic ocean section abstract major changes in temperature and tracer properties within the arctic ocean are evident in a comparison of data obtained during the 1994 arctic ocean section to earlier measurements 1 anomalously warm and well ventilated waters are now found in the nansen amundsen and makarov basins with the largest temperature differences as much as 1 c in the core of the atlantic layer 200 400 m thus thermohaline transition appears to follow from two distinct mechanisms narrow order 100 km topographically steered cyclonic flows that rapidly carry new water around the perimeters of the basins and multiple intrusions 40 60 m thick which extend laterally into the basin interiors 2 altered nutrient distributions that within the halocline distinguish water masses of pacific and atlantic origins likewise point to a basin wide redistribution of properties 3 distributions of cfcs associated with inflows from adjacent shelf regions and from the atlantic demonstrate recent ventilation to depths exceeding 1800 m 4 concentrations of the pesticide hch in the surface and halocline layers are supersaturated with respect to present atmospheric concentrations and show that the ice capped arctic ocean is now a source to the global atmosphere of this contaminant 5 the radionuclide 129i is now widespread throughout the arctic ocean although the current level of 129i level poses no significant radiological threat its rapid arrival and wide distribution illustrate the speed and extent to which waterborne contaminants are dispersed within the arctic ocean on pathways along which other contaminants can travel from western european or russian sources

gravity field and structures of the rajmahal hills example of the paleo mesozoic continental margin in eastern india abstract a narrow strip of gondwana basins separates the rajmahal traps from the peninsular shield in eastern india this part of the shield margin is associated with a conspicuous gravity high of 100 km wavelength and 48 mgal amplitude over an area of 25 000 km 2 second order residual anomalies due to gondwana sediments and traps are superposed on this wider gravity high gravity interpretation partly constrained by seismic data suggests that the wider high is caused by a denser metamorphic layer amphibolite and granulite up to 3 5 km thick the metamorphic layer also extends below the eastern rajmahal hills where the gondwanas traps and younger sediments have covered it the gondwanas are downfaulted against the shield edge and are preserved over an irregular basin floor whose deepest part underlies the eastern flank of the rajmahal hills adjacent to the bengal basin it is inferred that the gondwanas were deposited over a rifted and highly faulted shield margin that was intruded by the rajmahal traps nearly 100 m y ago high grade metamorphism along the shield edge presumably preceded the continental rifting perhaps occurring in the precambrian as a part of the eastern ghats orogeny along the east coast of india

saline outflow from the arctic ocean its contribution to the deep waters of the greenland norwegian and iceland seas abstractsince 1985 various investigators have proposed that norwegian sea deep water nsdw is formed by mixing of warm and saline deep water from the arctic ocean with the much colder and fresher deep water formed by convection in the greenland sea gsdw we here report on new observations which suggest significant modification and expansion of this conceptual model we find that saline outflows from the arctic ocean result in several distinct intermediate and deep salinity maxima within the greenland sea the southward transport of the two most saline modes is probably near 2 sv mixing of gsdw and the main outflow core found over the greenland slope derived from about 1700 m in the arctic ocean cannot by itself account for the properties of nsdw instead the formation of nsdw must at least in part involve a source which in the arctic ocean is found below 2000 m the mixing of various saline outflows is diapycnal while significant nsdw production appears to occur in northern fram strait large amounts of saline arctic ocean outflow also traverse the western greenland sea without mixing and enter the iceland sea during the past decade deep convection in the greenland sea has been greatly reduced while deep outflow from the arctic ocean appears to have continued resulting in a markedly warmer slightly more saline and less dense deep regime in the greenland sea american geophysical union 1991

transports of nordic seas water masses and excess sf6 through fram strait to the arctic ocean to determine the exchanges between the nordic seas and the arctic ocean through fram strait is one of the most important aspects and one of the major challenges in describing the circulation in the arctic mediterranean sea especially the northward transport of arctic intermediate water aiw from the nordic seas into the arctic ocean is little known in the two ship study of the circulation in the nordic seas arctic ocean 2002 the swedish icebreaker oden operated in the ice covered areas in and north of fram strait and in the western margins of greenland and iceland seas while rv knorr of woods hole worked in the ice free part of the nordic seas here two hydrographic sections obtained by oden augmented by tracer and velocity measurements with lowered acoustic doppler current profiler ladcp are examined the first section reaching from the svalbard shelf across the yermak plateau covers the region north of svalbard where inflow to the arctic ocean takes place the second western section spans the outflow area extending from west of the yermak plateau onto the greenland shelf geostrophic and ladcp derived velocities are both used to estimate the exchanges of water masses between the nordic seas and the arctic ocean the geostrophic computations indicate a total flow of 3 6 sv entering the arctic on the eastern section the southward flow on the western section is found to be 5 1 sv the total inflow to the arctic ocean obtained using the ladcp derived velocities is much larger 13 6 sv and the southward transport on the western section is 13 7 sv equal to the northward transport north of svalbard sulphur hexafluoride sf6 originating from a tracer release experiment in the greenland sea in 1996 has become a marker for the circulation of aiw from the geostrophic velocities we obtain 0 5 sv and from the ladcp derived velocities 2 8 sv of aiw flowing into the arctic the annual transport of sf6 into the arctic ocean derived from geostrophy is 5 kg year which is of the same magnitude as the observed total annual transport into the north atlantic while the ladcp measurements 19 kg year imply that it is substantially larger little sf6 was found on the western section confirming the dominance of the arctic ocean water masses and indicating that the major recirculation in fram strait takes place farther to the south

winter sea ice melting in the atlantic water subduction area svalbard norway herein we study a small area along the shelf west of spitsbergen near prins karls forland where warm saline atlantic water of the west spitsbergen current currently first encounters sea ice this sea ice is drifting in a coastal current that carries arctic water originating from the barents sea northward over the shelf our aim was to investigate whether melting of sea ice by atlantic water in this area might be a significant factor that could contribute to the formation of a cold halocline layer that isolates the sea ice from further melting from below observations of temperature and salinity profiles were collected during two winters via ctd srdl instruments deployed on harbor seals phoca vitulina and fed into a heat and freshwater budget box model in order to quantify the importance of melting relative to other processes that could transform the shelf water mass during winter cross frontal exchange of atlantic water from the west spitsbergen current driven by buoyancy forcing rather than ekman upwelling was determined to be the source of the heat that melted drift ice on the shelf some local sea ice formation did take place but its importance in the total heat and freshwater budgets appeared to be minor the data suggest that the production of a cold halocline layer was preceded by southerly winds and rapid drift ice melting

crustal structure of bengal basin and shillong plateau extension of eastern ghat and satpura mobile belts to himalayan fronts and seismotectonics abstract gravity data from the east india and the bangladesh are processed and compiled together to provide a composite complete bouguer anomaly map of this region modelling of gravity profiles across the east indian shield chhotanagpur granite gneiss complex cggc the shillong plateau and the bengal basin in bangladesh constrained from seismic studies suggest crustal thickness of 37 38 km and thrusted high density rocks in the middle crust under the east indian shield reducing to 30 32 km with thick sediments of 12 14 km under bangladesh reduced crustal thickness under bangladesh is attributed to oceanic type of crust which is connected to indian continent along hinge zone characterized by linear gravity highs connecting east coast of india to the shillong plateau thrusted high density rocks under the cggc and the shillong plateau are in comparison to those under the eastern ghat and the satpura mobile belts egmb smb respectively suggest the north ward and east ward extensions of these orogenies margins of the thrusted block under shillong plateau when projected on surface coincide approximately with the south dipping dauki and the brahmaputra faults which coincides with central bulge due to lithospheric flexure indicating their surface expositions

boundary undercurrent and water mass changes in the lincoln sea oceanographic measurements taken between 1989 and 1994 in the lincoln sea describe the currents and water mass structure along the continental slope of the arctic basin between the canadian and eurasian basins the measurements included periodic conductivity and temperature versus depth ctd profiles from ice camps ctd cross sections normal to the slope and year round current measurements analysis of this data describes the hydrographic structure of the waters over the continental slope and identifies some significant interannual variations an undercurrent confined to the continental slope with a width of about 50 km and speeds of 5 9 cm s 1 is shown in geostrophic current cross sections the presence of this easterly flow at depth is confirmed by current meter measurements and its existence has also been observed in the beaufort sea and the barents sea aagaard 1989 the waters within this undercurrent exhibit temperature salinity ts characteristics similar to canadian basin waters suggesting a boundary current system which is continuous along the continental slope north of alaska and canada significant interannual variations in temperature and salinity profiles may be related to variations in the large scale circulation of the arctic examination of the upper pycnocline waters over the slope between 1991 and 1994 indicated a relative temperature maximum overlying a minimum ts characteristics similar to waters attributed to bering sea origin found in the canadian basin these characteristics were not seen however during 1989 and 1990 suggesting a recent increase in the transport of surface waters from the canadian basin into the eurasian basin

penetration of the 1990s warm temperature anomaly of atlantic water in the canada basin 1 penetration of the 1990s warm temperature anomaly wta of the fram strait branch of atlantic water fsbw in the canada basin is described using available temperature salinity and velocity data the core temperatures of fsbw show distinct pathways over the chukchi borderland advective velocities of the fsbw are well correlated with bottom topography the resulting multifarious pathways over the chukchi borderland act to modulate and substantially increase the time scale of wta spreading and advancement further downstream two wta tongues are observed one tongue followed the beaufort slope and along this pathway the core temperatures of fsbw decreased rapidly the depth integrated value of heat content remained near constant however suggesting enhanced vertical mixing the second tongue debouched from the northern tip of the northwind ridge and spread eastward into the deep canada basin suggesting a complex recirculation structure within the beaufort gyre index terms 4532 oceanography physical general circulation 4536 oceanography physical hydrography 4512 oceanography physical currents citation shimada k f mclaughlin e carmack a proshutinsky s nishino and m itoh 2004 penetration of the 1990s warm temperature anomaly of atlantic water in the canada basin geophys res lett 31 l20301

deepening of the atlantic water core in the canada basin in 2003 11 abstractin 2004 a cold mode of atlantic water aw entered the western canada basin replacing the anomalously warm aw that resided in the basin since the 1990s this slightly colder aw was denser than the 1990s warm mode it gradually filled most of the western basin by 2009 the enhanced surface stress curl led to the spinup of the beaufort gyre and convergence of freshwater the spinup also resulted in a deepening of the aw core at the center of the gyre and in shoaling of the aw core at the margins of the gyre the density versus depth relationship revealed in this study shows that the depth of the maximum aw temperature was mainly controlled by the density structure before 2007 thus it is the case when the denser water was deeper and the case when the lighter water was shallower around the basin however this relationship was reversed to become the case when the denser water was shallower and the case when the lighter water was deeper since 2008 inside the beaufort gyre the combined effect of de

distribution of atlantic and pacific waters in the upper arctic ocean implications for circulation the atlantic and pacific oceans provide source waters for the arctic ocean that can be distinguished by their differing nitrate and phosphate concentration relationships using these relationships we estimate the amount of atlantic and pacific waters in the surface layer top 30 m of the arctic ocean atlantic source water is dominant in most of the eurasian basin and is present in significant amounts in the makarov basin north of the east siberian sea pacific source water is dominant in most of the canadian basin and is present in significant amounts in the amundsen basin north of greenland we deduce circulation patterns from the distributions of atlantic and pacific source waters in the surface layer of the arctic ocean and conclude that the flow within the surface layer differs from ice drift along the north american and european boundaries of the polar basin

plio pleistocene trends in ice rafted debris on the lomonosov ridge although more than 700 sediment cores exist from the arctic ocean the plio pleistocene evolution of the basin and its marginal seas remains virtually unknown this is largely due the shallow penetration of most of these records and difficulties associated with deriving chronologies for the recovered material the integrated ocean drilling program s iodp expedition 302 arctic coring expedition acex recovered 197 m of neogene quaternary sediment from the circumpolar regions of the lomonosov ridge as detailed analyses of this material emerge research is beginning to formulate a long term picture of paleoceanographic changes in the central arctic ocean this paper reviews the acex plio pleistocene age model identifies uncertainties and addresses ways in which these may be eliminated within the established stratigraphic framework a notable reduction in the abundance of ice rafted debris ird occurs in the early part of the pleistocene and persists until marine isotope stage 6 mis 6 therefore while global oceanographic proxies indicate the gradual growth of terrestrial ice sheets during this time ird delivery to the central arctic ocean remained comparatively low and stable within the resolution of existing data the pleistocene reduction in ird is synchronous with predicted changes in both the inflow of north atlantic and pacific waters which in modern times are known to exert a strong influence on sea ice stability

seasonal surface layer dynamics and sensitivity to runoff in a high arctic fjord young sound tyrolerfjord 74 n runoff from the greenland ice sheet local glaciers and snowmelt along the northeastern greenland coastline has a significant impact on coastal water masses flowing south toward denmark strait very few direct measurements of runoff currently exist in this large area and the water masses near the coast are also difficult to measure due to the presence of icebergs and sea ice measurements from the zackenberg research station located in young sound tyrolerfjord in northeast greenland 74 n provide some of the few observations of hydrographic hydrologic and atmospheric parameters from this remote area here we analyze measurements from the fjord and also measurements in the ambient water masses which are found in the outer fjord and between the fjord and the east greenland current and validate and apply a numerical model of the fjord a model sensitivity study allows us to constrain runoff estimates for the area we also show that a total runoff between 0 9 and 1 4 km3 in 2006 is in accordance with observed surface salinities and calculated freshwater content in the fjord this indicates that earlier reported runoff to the area is significantly underestimated and that melt from glaciers and the greenland ice sheet in this region may be up to 50 larger than the current estimate model simulations indicate the presence of a cold low saline coastal water mass formed by runoff from fjords north of the young sound tyrolerfjord system simulations of passive and age tracers show that residence time of river water during the summer period is about 1 month in the inner part of the fjord

water mass distribution and polar front structure in the western barents sea the water mass distribution in the western barents sea the thermohaline structure of the western barents sea polar front and the local formation of a dense water mass are described on the basis of an analysis of historical hydrographic data this study concentrated on the frontal region between bjornoya and hopen island where arctic water is found on the spitsbergen bank and atlantic water in the bear island trough and hopen trench the distributions of atlantic and arctic waters in relation to topography were consistent with the hypothesis that the location of the polar front is fixed at about the 250 m isobath by the barotropic circulation of atlantic water within the bear island trough and hopen trench in winter vertical gradients of temperature and salinity were weak throughout the frontal region consistent with a barotropic topographically controlled front in summer vertical gradients remained weak below 100 m depth but increased in the upper layer as a result of the presence of fresh warm surface water produced by melting ice the topographic control of thermohaline properties at the surface was disrupted by the meltwater pool and the meltwater contributed to water mass modification in the frontal region the following seasonal cycle of water mass formation was hypothesized summer heating melts the sea ice on the spitsbergen bank and produces the surface meltwater pool this meltwater not only increases vertical thermohaline gradients on the bank but also crosses the front and freshens the surface layer throughout the western barents sea subsequent winter cooling which creates ice over the bank also forms dense water in the bear island trough and hopen trench by convective mixing of atlantic water and the overlying meltwater

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

audiomagnetotelluric studies to trace the hydrological system of thermal fluid flow of bakreswar hot spring eastern india a case history an audiomagnetotelluric amt study has been carried out in the bakreswar hot spring bhs area of eastern india to locate the geothermal source in the vicinity of bhs phase tensor analysis of the amt data shows that the region is broadly 2d rapid relaxation inversion rri for both transverse electric te and transverse magnetic tm modes has been carried out to obtain resistivity images of the subsurface amt results show that the north south fault close to bakreswar is a shallow feature not deeper than 300 m and thus cannot act as a heat source the subsurface formation below the fault zone is highly resistive up to a great depth indicating the absence of a heat source and geothermal reservoir in the vicinity of the bhs amt results indicate that the location of the geothermal reservoir is deep and lies beyond the profiles of measurement in the northwestern side of the bakreswar hot spring

the role of sea ice and other fresh water in the arctic circulation salinity stratification is critical to the vertical circulation of the high latitude ocean we here examine the control of the vertical circulation in the northern seas and the potential for altering it by considering the budgets and storage of fresh water in the arctic ocean and in the convective regions to the south we find that the present day greenland and iceland seas and probably also the labrador sea are rather delicately poised with respect to their ability to sustain convection small variations in the fresh water supplied to the convective gyres from the arctic ocean via the east greenland current can alter or stop the convection in what may be a modern analog to the halocline catastrophes proposed for the distant past the north atlantic salinity anomaly of the 1960s and 1970s is a recent example it must have had its origin in an increased fresh water discharge from the arctic ocean similarly the freshening and cooling of the deep north atlantic in recent years is a likely manifestation of the increased transfer of fresh water from the arctic ocean into the convective gyres finally we note that because of the temperature dependence of compressibility a slight salinity stratification in the convective gyres is required to efficiently ventilate the deep ocean

on the ice and heat balance in fram strait the sea ice margin northwest of spitsbergen is schematically represented by a stationary wedge maintained by opposing ice and warm atlantic water advection ice melt and cooling of the surface water generate a mixed layer with properties approximating those found elsewhere in the arctic basin the heat energy required to melt the advancing ice is roughly comparable to the rate of heat loss of the west spitsbergen current and suggests that direct heat exchange with the atmosphere is less important only a small fraction of the nearly fresh water from ice melt exits through eastern fram strait and most of it appears to return to the arctic basin whether or not it contributes to the formation and maintenance of the arctic mixed layer depends on the largely unknown circulation pattern north of fram strait an example of the large interannual variation of the mean wind stress field is shown to illustrate the likelihood of an equally large variance of the ice and surface water circulation

retreat of the cold halocline layer in the arctic ocean we present a comparison of arctic ocean hydrographic data sets from the 1990s with a focus on changes in the upper few hundred meters of the eurasian basin the most recent observations discussed here were collected during the spring 1995 scientific ice expedition scicex 95 the second in a series of scientific cruises to the arctic ocean aboard u s navy nuclear submarines although the 1990s have seen an abundance of synoptic cruises to the arctic this was the only one to take place in winter spring conditions other data considered here were collected during the first scicex cruise in summer 1993 scicex 93 and during an icebreaker cruise to the eurasian basin in summer 1991 oden 91 a new russian american winter climatology is also used as a reference these comparisons reveal that the eurasian basin cold halocline layer has retreated during the 1990s to cover significantly less area than in previous years specifically we find a retreat from the amundsen basin back into the makarov basin the latter is the only region with a true cold halocline layer during scicex 95 changes are also seen in other halocline types and in the atlantic water layer heat content and depth since the cold halocline layer insulates the surface layer and thus the overlying sea ice from the heat contained in the atlantic water layer this should have profound effects on the surface energy and mass balance of sea ice in this region using a simple mixing model we calculate maximum ice ocean heat fluxes of 1 3 w m 2 in the eurasian basin where during scicex 95 the surface layer lay in direct contact with the underlying atlantic water layer the overall cause of water mass changes in the 1990s might have been a shift in the atmospheric wind forcing and resulting sea ice motion during the late 1980s which we speculate influenced the location where fresh shelf waters flow into the deeper basins of the arctic ocean finally we discuss two different mechanisms that have been proposed for cold halocline water formation and we propose a compromise that best fits these data

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

synoptic sections of the denmark strait overflow we report on a rapid high resolution survey of the denmark strait overflow dso as it crosses the sill the first such program to incorporate full water column velocity profiles in addition to conventional hydrographic measurements seven transects with expendable profilers over the course of one week are used to estimate volume transport as a function of density our observations reveal the presence of a strongly barotropic flow associated with the nearly vertical front dividing the arctic and atlantic waters the seven section mean transport of water denser than 27 8 is 2 7 0 6sv while the mean transport of water colder than 2 0 c is 3 8 0 8 sv although this is larger than the 2 9 sv of 2 c water measured by a 1973 current meter array we find that a sampling of our sections equivalent to the extent of that array also measures 2 9sv of cold water both the structure and magnitude of the measured flow are reproduced well by a high resolution numerical model of buoyancy driven exchange with realistic topography

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

contour current driven continental slope situated sandwaves with effects from secondary current processes on the barents sea margin offshore norway abstract seabed data acquired from the southern barents sea continental margin offshore norway reveal detailed morphology of large sandwave fields multibeam echosounder bathymetry and backscatter shallow seismic sediment samples and seabed video data collected by the mareano program have been used to describe and interpret the morphology distribution and transport of the sandwaves the bedforms lie on a slope dominated by relict glacial forms and muddy sandy gravelly sediments sandwave migration across small gravity mass failures of the glacial mud constrains the field initiation as early post glacial or later the contour parallel nature of the fields and crestlines normal to the bathymetry contours and the geostrophic norwegian atlantic current nwac demonstrate that the nnw flowing oceanographic circulation is the primary driving current the fields coincide with the depth range at which a transition between warm saline and underlying cooler less saline waters fluctuate across the seabed statistically rigorous measurements of height width and various parameters of slope and symmetry confirm a tendency to downstream nnw sandwave migration but with significant exceptions anomalous bedform symmetry domains within the fields are tuned to meso scale topography along relict glacial debris flow chutes indicating current focusing upstream and upper slope derived winnowed sand transport eroded from the glacial sediments is the supposed source sandwave flank slope values are comparable to the regional slope such that the gravitational vector would have a cumulative downslope migration affect unless balanced by upslope drivers perpendicular cross cutting of stoss face 3 d ripples by linear 2 d ripples in the sandwave troughs and lee faces is evidence for non synchronous episodic current variations though deep ekman transport and internal wave action are unproven here these could explain chute related tuning of bedform symmetry through funneling in the debris flow chutes and favor sand recycling thus contributing to long term maintenance of the sandwave field

waters of the makarov and canada basins abstract hydrographic measurements from the 1994 arctic ocean section show how the makarov and canada basins of the arctic ocean are related and demonstrate their oceanographic connections to the eurasian basin the inflow into the makarov basin consists largely of well ventilated water within a broad band of densities from a boundary flow over the siberian end of the lomonosov ridge the boundary flow contains a significant component of dense shelf water likely originating in the barents kara and laptev seas earlier ice camp data show that the canada basin is relatively more isolated from this ventilation source in the canada basin shelf sources influenced by bering sea water appear to add cold waters with high silicate concentrations to the halocline and deeper in 1994 the halocline silicate maximum over the central makarov basin was absent evidence of the recent displacement of the upper s 33 1 halocline water from the chukchi east siberian sea region by water from the eurasian basin much of the makarov basin water in and below the halocline is in fact from the eurasian basin with admixture of waters from the canada basin suggested by their higher silicate concentrations mid depth eddies may transport anomalous properties into the central arctic and create property gradients or fronts in mid depth and deep waters the complex topography of the mendeleyev ridge chukchi plateau region also may assist spreading of water from the boundary into the interior atlantic layer characteristics in 1994 differed from previous general depictions in particular the core temperatures at the chukchi mendeleyev boundary were at least 0 2 c warmer on average than indicated in earlier work the recent warming at intermediate depth has resulted from inflow of atlantic waters that have been cooled relatively little during their transit of the norwegian sea

sources to the east greenland current and its contribution to the denmark strait overflow data from the east greenland current in 2002 are evaluated using optimum multiparameter analysis the current is followed from north of fram strait to the denmark strait sill and the contributions of different source waters in mass fractions are deduced from the results it can be concluded that at least in spring 2002 the east greenland current was the main source for the waters found at the denmark strait sill contributing to the overflow into the north atlantic the east greenland current carried water masses from different source regions in the arctic ocean the west spitsbergen current and the greenland sea the results agree well with the known circulation of the western nordic seas but also add knowledge both to the quantification and to the mixing processes showing the importance of the locally formed greenland sea arctic intermediate water for the east greenland current and the denmark strait

arctic ocean water mass balance from isotope data the distributions of the oxygen 18 and tritium isotopes and of salinity yield a residence time of 10 years for the surface and halocline waters of the arctic basin we find a yearly net production of 0 59 m of sea ice and an input of 1 16 m of freshwater from continental river runoff local precipitation and bering strait salinity deficiency using the basin area value with these numbers gives long term average total net production and transport rates of 0 15 sv of ice and 0 18 sv of meteoric component bering strait water not included if in addition a reasonable depth profile of relative current velocity is assumed for the outflow a yearly input of 2 8 sv of atlantic and bering strait water is needed to replenish the upper and halocline waters these numbers should be good to 20 and are multiyear averages the isotope data clearly indicate that the barents sea is an inflow area for atlantic water to the basin but that net export of ice occurs there

changes in the flow of atlantic water into the arctic ocean since the last deglaciation evidence from the northern svalbard continental margin 80 n 1 the svalbard archipelago is located in the high arctic 76 80 n within the northernmost reach of the west spitsbergen current which is the continuation of the north atlantic current in this specific setting close to the polar front even small variations in the current system are expected to give large and distinct signals in paleoceanographic parameters thus the svalbard area is ideal for monitoring the past history of the inflow of atlantic water to the arctic ocean we have studied sediment core np94 51 taken outside the mouth of the hinlopen strait on the northern svalbard shelf the paleoceanographic development of the last deglaciation and the holocene has been reconstructed using benthic and planktonic foraminifera oxygen isotopes and ice rafted detritus the results show that the first strong subsurface inflow of atlantic water to the arctic ocean after the last glacial maximum commenced at 12 6 14c kyr b p circa 15 000 calendar cal years b p during the bolling allerod interstadial during the younger dryas polar conditions prevailed at the surface with extensive sea ice cover and the inflow of atlantic derived water was generally diminished the inflow of more saline but still cold atlantic water was relatively strong during the early holocene and caused intensified seasonal biological productivity the atlantic water inflow declined gradually during the mid holocene between 4500 and 1100 cal years b p the inflow was very weak and the bottom waters over the northern svalbard margin were cold and of lower salinity during the last 1000 years climatic conditions improved such that the subsurface inflow of atlantic derived water increased however the surface waters were still cold

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 interior shelves of the arctic ocean physical oceanographic setting climatology and effects of sea ice retreat on cross shelf exchange abstract the interior shelves of the arctic mediterranean are the shelves of the kara sea laptev sea east siberian sea and beaufort sea they comprise approximately 40 of the total arctic shelf area 2 5 10 6 km 2 and are distinguished from inflow and outflow shelves by their principal forcing dynamics along their southern continental boundary the interior shelves are dominated by the major arctic rivers receiving over 80 of the total freshwater input to the arctic ocean in the mid shelf region wind and ice motion surface stresses dominate mixing and circulation resulting in high variability along their northern seaward boundary they are forced by upwelling and downwelling favourable surface stresses which drive shelf basin exchanges with atlantic and pacific origin cyclonic boundary currents over the upper slope shelf basin exchange is further modified by shelf break morphometry e g canyons valleys headlands and bottom slope here we review the physical oceanographic settings and forcing of the interior shelves and then focus on shelfbreak exchange and supply of nutrients for new primary production due to upwelling across the shelfbreak as a proxy for this nutrient supply we show seasonal and annual time series of along shelfbreak surface stress due to wind and ice motion from 1979 to 2011 we apply this analysis to the shallow shelves from the kara sea to the beaufort sea and comment on recent increases due to atmospheric changes and sea ice retreat

ocean circulation and freshwater pathways in the arctic mediterranean based on a combined nd isotope ree and oxygen isotope section across fram strait the water masses passing the fram strait are mainly responsible for the exchange of heat and freshwater between the nordic seas and the arctic ocean the arctic mediterranean am disentangling their exact sources distribution and mixing however is complex this work provides new insights based on a detailed geochemical tracer inventory including dissolved nd isotope end rare earth element ree and stable oxygen isotope 18o data along a full water depth section across fram strait we find that nd isotope and ree distributions in the open am primarily reflect lateral advection of water masses and their mixing seawater particle interactions exert important control only above the shelf regions as observed above the ne greenland shelf advection of northward flowing warm atlantic water aw is clearly reflected by an end signature of 11 7 and a nd concentration nd of 16 pmol kg in the upper 500 m of the eastern and central fram strait freshening and cooling of the aw on its way trough the am are accompanied by a continuous change towards more radiogenic end signatures e g 10 4 of dense arctic atlantic water this mainly reflects mixing with intermediate waters but also admixture of dense kara sea waters and pacific derived waters the more radiogenic end signatures of the intermediate and deep waters reaching 9 5 are mainly acquired in the sw nordic seas through exchange with basaltic formations of iceland and se greenland inputs of nd from svalbard are not observed and surface waters and nd on the svalbard shelf originate from the barents sea shallow southward flowing arctic derived waters 200 m form the core of the east greenland current above the greenland slope and can be traced by their relatively radiogenic end reaching 8 8 and elevated nd 21 to 29 pmol kg these properties are used together with 18o and standard hydrographic tracers to define the proportions of pacific derived 30 based on nd isotopes and atlantic derived waters as well as of river waters 8 shallow waters 150 m on the ne greenland shelf share some characteristics of arctic derived waters but exhibit less radiogenic end values reaching 12 4 and higher nd up to 38 pmol kg in the upper 100 m this suggests local addition of greenland freshwater of up to 6 in addition to these observations this study shows that the pronounced gradients in end signatures and ree characteristics in the upper water column provide a reliable basis for assessments of shallow hydrological changes within the am

evolution of the freshwater coastal current at the southern tip of greenland abstractshipboard hydrographic and velocity measurements collected in summer 2014 are used to study the evolution of the freshwater coastal current in southern greenland as it encounters cape farew

physical and biological characteristics of the pelagic system across fram strait to kongsfjorden abstract the fram strait is very important with regard to heat and mass exchange in the arctic ocean and the large quantities of heat carried north by the west spitsbergen current wsc influence the climate in the arctic region as a whole a large volume of water and ice is transported through fram strait with net water transport of 1 7 3 2 sv southward in the east greenland current and a volume ice flux in the range of 0 06 0 11 sv the mean annual ice flux is about 866 000 km2 yr 1 the kongsfjorden krossfjorden fjord system on the coast of spitsbergen or at the eastern extreme of fram strait is mainly affected by the northbound transport of water in the wsc mixing processes on the shelf result in transformed atlantic water in the fjords and the advection of atlantic water also carries boreal fauna into the fjords the phytoplankton production is about 80 g c m 2 yr 1 in fram strait and has been estimated both below and above this for kongsfjorden the zooplankton fauna is diverse but dominated in terms of biomass by calanoid copepods particularly calanus glacialis and c finmarchicus other important copepods include c hyperboreus metridia longa and the smaller more numerous pseudocalanus p minutus and p acuspes microcalanus m pusillus and m pygmaeus and oithona similis the most important species of other taxa appear to be the amphipods themisto libellula and t abyssorum the euphausiids thysanoessa inermis and t longicaudata and the chaetognaths sagitta elegans and eukrohnia hamata a comparison between the open ocean of fram strait and the restricted fjord system of kongsfjorden krossfjorden can be made within limitations the same species tend to dominate but the fram strait zooplankton fauna differs by the presence of meso and bathypelagic copepods the seasonal and inter annual variation in zooplankton is described for kongsfjorden based on the record during july 1996 2002 the ice macrofauna is much less diverse consisting of a handful of amphipod species and the polar cod the ice associated biomass transport of ice amphipods was calculated based on the ice area transport at about 3 55 106 ton wet weight per year or about 4 2 105 t c yr 1 this represents a large energy input to the greenland sea but also a drain on the core population residing in the multi year pack ice myi in the arctic ocean a continuous habitat loss of myi due to climate warming will likely reduce dramatically the sympagic food source the pelagic and sympagic food web structures were revealed by stable isotopes the carbon sources of particulate organic matter pom being ice pom and pelagic pom revealed different isotopic signals in the organisms of the food web and also provided information about the sympagic pelagic and pelagic benthic couplings the marine food web and energy pathways were further determined by fatty acid trophic markers which to a large extent supported the stable isotope picture of the marine food web although some discrepancies were noted particularly with regard to predator prey relationships of ctenophores and pteropods

upwelling at the ice edge a mechanism for deep water formation this study sets forward a hypothesis which anticipates deep water formation due to ice edge upwelling the upwelling can raise thermocline waters the lower arctic intermediate water to the surface or near it where the water is exposed to cooling evaporation mixing and oxygenation thus upwelling can act as a preconditioning mechanism for deep convection the conjecture would also explain the salinity range of the greenland sea deep water if the upper and lower arctic intermediate water masses are mixed so that the latter has at least an 80 contribution also the convection events induced by ice edge upwelling during winter season we anticipate could give rise to a new deep water annual production rate consistent with observations

outflow of dense water from the storfjord in svalbard a numerical model study recent investigations on deep water renewal point to the important role of dense water formed on the continental shelves surrounding the arctic ocean in this investigation a hydrostatic reduced gravity primitive equation model for the simulation of the spatial and temporal evolution of gravity plumes on a continental slope is applied and compared to the observed outflow of a plume of dense water originally formed in storfjorden svalbard into the greenland sea toward fram strait the vertically integrated nonlinear rotational model accounts for the entrainment of water mass properties from a spatially structured but stagnant ambient water body this study reveals that part of the dense water in accordance with earlier estimates spreads northward along the eastern side of fram strait another branch of the plume guided by the topography flows into a deep trench east of the knipovitch ridge to the west of svalbard during its descent to depths of more than 2000 m the plume entrains three different water masses east spitsbergen water atlantic water and norwegian sea deep water and hence changes its water mass characteristics the volume of deep water produced by the mechanism discussed here depends not only on the amount of initially formed brine enriched shelf water but also on the water mass characteristics of the latter

freshwater distribution in the arctic ocean simulation with a high resolution model and model data comparison 1 a high resolution numerical simulation of the arctic ocean is analyzed in order to study the fate of river runoff and freshwater fluxes in the arctic ocean the model is driven by realistic winds and thermodynamic forcing from the european centre for medium range weather forecasting ecmwf reanalysis data set dye tracers have been added to visualize the pathways followed by low salinity water from the major arctic rivers and bering strait inflow the model is spun up using repeated forcing with the 1979 annual cycle for 20 years then the 1979 through 1998 atmospheric forcing is applied under the influence of the 1979 through early 1980s winds a large plume of river runoff exits the broad eurasian shelf seas along the lomonosov ridge starting in about 1985 the locus of shelf to basin transport shifts eastward to the alpha mendeleyev ridge complex this shift in the model output is related to changes in the sea surface height ssh fields which we attribute primarily to shifts in surface wind stresses model resolution runoff inputs and relaxation terms in the lena river delta region are analyzed in detail to expose issues with model performance at boundaries with freshwater inflow suggestions are made for improving future simulations of river runoff in basin scale models

the west spitsbergen current disposition and water mass transformation recent work suggests that the west spitsbergen current which provides the principal contribution to the arctic ocean of salt and sensible heat as well as of a variety of anthropogenic tracers is a rather complex circulation feature north of 79 n where the isobaths diverge markedly the current contains two separate warm cores that follow different isobaths the western core carried by the offshore branch of the current follows the western flank of the yermak plateau and north of 80 n at least part of this flow detaches from the plateau probably to contribute to the recirculation in fram strait in contrast the inshore branch follows the shelf break into the arctic ocean it is this inshore branch that provides the primary focus in this paper during the transit of the inshore waters past northwestern spitsbergen the core properties change primarily through vertical heat flux which during ice free conditions in winter is estimated to be of the order of 200 w m 2 from the core layer alone together with some freshening within the arctic ocean this process is responsible for fully transforming the original atlantic water into arctic intermediate water within about 600 km of fram strait

morphotectonic configuration of cratonic gondwana depocentres of eastern india abstract the bouguer anomaly over parts of the intra cratonic gondwana grabens of eastern india namely the damodar valley the eastern deogarh the southern rajmahal and the western margin of the peri cratonic external foredeep of west bengal has been analysed in terms of subsurface geology and tectonics we have identified three new gondwana troughs under the tertiary cover and have unveiled the probable subcrop pattern of the concealed cretaceous trap and the underlying gondwana sediments the shoulders of these permo carboniferous rift basins are characterised by high gravity anomalies suggesting the occurrences of high density hybrid rock masses outcrops of such hybrid rocks archean mostly metabasic in composition are actually seen at several places along the different rift shoulders two dimensional gravity modelling indicates that these high density 2 90 gm cm3 masses occur as enclaves at shallow depths 0 5 3 0 km within the upper crustal layer we believe that these anomalous masses have played a key role in the evolution of the various gondwana rift basins by controlling their width and guiding their propagation the present study supports a deep mantle plume generated triple arm rift basin geometry for this sedimentological province

paleoceanographic evolution of the sw svalbard margin 76 n since 20 000 14c yr bp abstract two cores from the southwestern shelf and slope of storfjorden svalbard taken at 389 m and 1485 m water depth have been analyzed for benthic and planktic foraminifera oxygen isotopes and ice rafted debris the results show that over the last 20 000 yr atlantic water has been continuously present on the southwestern svalbard shelf however from 15 000 to 10 000 14c yr bp comprising the heinrich event h1 interval the bolling allerod interstades and the younger dryas stade it flowed as a subsurface water mass below a layer of polar surface water in the benthic environment the shift to interglacial conditions occurred at 10 000 14c yr bp due to the presence of a thin upper layer of polar water surface conditions remained cold until ca 9000 14c yr bp when the warm atlantic water finally appeared at the surface neither extensive sea ice cover nor large inputs of meltwater stopped the inflow of atlantic water its warm core was merely submerged below the cold polar surface water

arctic ocean record of last two glacial interglacial cycles off north greenland ellesmere island implications for glacial history a sediment record from the practically unknown southernmost part of the lomonosov ridge off north greenland ellesmere island has been studied greenice core 10 encompasses marine isotope stages mis 7 1 and reveals changing paleoceanographic conditions and land ocean connections during the last two glacial interglacial cycles the isotope record of planktic foraminifera neogloboquadrina pachyderma s show large similarities to other arctic ocean key records supporting that the pattern reflect over regional changes of the halocline structure the relatively low 18 o values of subpolar foraminifera turborotalita quinqueloba in the last interglacial unit support that the specimens represent local production related to warm interglacial conditions and a reduced sea ice cover in the interior arctic ocean enhanced deposition of coarse ice rafted debris took place during the mis 8 7 transition periods of mis 6 mis 6 5 transition mis 5d mis 4 and late mis 3 30 40 14 c kyr bp in mis 2 ird flux was low in the area the ird contains detrital carbonate similar to other amerasia basin records the occurrence of finegrained calcite rich detrital carbonate layers at glacial interglacial transitions seems unique to this area we suggest that detrital carbonate was transported and deposited from nepheloid flows during deglaciations of ellesmere island when the atlantic water boundary current along the continental margin was gaining strength 2007 elsevier b v all rights reserved

formation and evolution of the surface mixed layer and halocline of the arctic ocean fresh water from summer ice melt and the total freshwater content of the arctic ocean water column above the thermocline are estimated from vertical profiles of temperature and salinity observed on the i b oden 1991 cruise the seasonal ice melt ranges from 0 5 m to slightly above 1 m and is moderately uniform over the observation area regions of lower melting are seen over the morris jesup plateau the freshwater content is calculated relative to the salinity just above the thermocline north of the barents sea the freshwater content increases toward the interior of the arctic ocean showing that fresh water is advected from other regions into the observation area regions of different freshwater content are separated by fronts over the nansen gakkel ridge over the lomonosov ridge and in the western eurasian basin between waters derived from the eurasian and canadian basins denser water homogenized north of the barents sea is recognized by a temperature minimum layer the absence of the temperature minimum near the nansen gakkel ridge indicates that heat is transferred from the atlantic layer over a longer time than the shortest route would allow this observation can be explained if the layer circulates together with the atlantic layer i e toward the east and returns above the nansen gakkel ridge and along the amundsen basin north of the laptev sea this water formed north of the barents sea becomes covered by low salinity shelf water the increased freshwater content limits the winter convection so it no longer reaches the thermocline and an intermediate halocline is formed the halocline in the eurasian basin consists of water originating from winter convection in the arctic ocean north of the barents sea which then circulates around the basin such a formation mechanism also explains the observed distribution of low no water the strong density increase limits vertical exchange and the vertical diffusion coefficient in the halocline is small 1 10 6 m2 s 1 the increased temperature of the halocline shows that the heat lost upward by the atlantic layer mainly by double diffusive convection is trapped below the mixed layer

evolution of a mediterranean salt lens scalar properties abstract the evolution of a mediterranean salt lens meddy over a two year period is examined several nondimensional numbers can be used to describe the overall decay in the structure of the moddy two rossby numbers one using the central relative vorticity and another using the radius and velocity of the azimuthal velocity maximum did not change over the two year period however the burger number n2h2 f2l2 increased as the meddy decayed another burger number the ratio of total kinetic energy to total available potential energy decreased from 1 1 to 0 6 over a one year period the rates at which the meddy lost salt and heat are consistent with estimates of horizontal fluxes by intrusions a horizontal diffusivity of o 5 m2 s 1 is needed if this flux by intrusions is parameterized by an eddy coefficient simple models of the evolution of an isolated eddy by horizontal and vertical mixing of mass and momentum are examined these simple attempts to explain the evolution of the meddy suggest more c

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

the velocity and mixing time scale of the arctic ocean boundary current estimated with transient tracers 1 the arctic ocean boundary current aobc is a persistent large scale feature of arctic circulation that transports water of atlantic origin around the eurasian and canadian basins despite its importance as a link between north atlantic sea surface temperature and the heat budget of the arctic ocean elements of the pathways of the aobc are still not well understood here we use transient tracer data collected during the 1990s at 22 locations to calculate the velocity and mixing time scale of the aobc the apparent spreading velocity derived from correlating 3h 3he ages in the barents sea branch water bsbw with the distance from its entry point at the santa anna trough is 0 9 cm s 1 to correct this apparent velocity for the effects of mixing along the pathway the aobc is modeled as a leaky pipe and 3h 3he and chlorofluorocarbon data are used to calculate the parameters of its transit time distribution function the modeled velocity of the aobc is 2 5 0 5 cm s 1 and the time scale for mixing of waters between the core of the boundary current and the adjacent water masses is 5 10 years these results imply that the advective time for transport around the perimeter of the arctic ocean from the santa anna trough to the southern canada basin approximately 6000 km is 7 5 years and the amplitude of a temperature anomaly or salinity anomaly in bsbw should decrease by 50 75 along this path

transport and transformation of riverine neodymium isotope and rare earth element signatures in high latitude estuaries a case study from the laptev sea abstract marine neodymium nd isotope and rare earth element ree compositions are valuable tracers for present and past ocean circulation and continental inputs yet their supply via high latitude estuaries is largely unknown here we present a comprehensive dissolved nd isotope expressed as end values and ree data set together with seawater stable oxygen isotope 18 o compositions of samples from the laptev sea recovered in two arctic summers and one winter the laptev sea is a shallow siberian shelf sea characterized by extensive river runoff sea ice production and ice transport into the arctic ocean the large variability in end 6 to 17 ree concentrations 16 to 600 pmol kg for nd and ree patterns is controlled by freshwater supply from distinct riverine sources and open ocean arctic atlantic water strikingly and contrary to expectations except for cerium no evidence for significant release of rees from particulate phases is found which is attributed to low amounts of suspended particulate matter and high dissolved organic carbon concentrations present in the contributing rivers essentially all shelf waters are depleted in light l rees while the distribution of the heavy rees shows a deficiency at the surface and a pronounced excess in the bottom layer this distribution is consistent with ree removal through coagulation of riverine nanoparticles and colloids starting at salinities near 10 and resulting in a drop of all ree concentrations by 30 with increasing salinity preferential lree removal is observable reaching 75 for nd at a salinity of 34 although the delayed onset of dissolved ree removal contrasts with most previous observations from other estuarine environments it agrees remarkably well with results from recent experiments simulating estuarine mixing of seawater with organic rich river waters in addition melting and formation of sea ice leads to further ree depletion at the surface and strong ree enrichment near the shelf bottom as a function of ice melting and brine transfer respectively the ice related processes significantly affect the distribution of dissolved rees in high latitude estuaries and likely also similarly contribute to the redistribution of other dissolved seawater constituents

tracing water masses with 129i in the western nordic seas in early spring 2002 two long lived halogen radionuclides 36cl t1 2 301 kyr and 129i t1 2 15 7 myr have been studied by means of accelerator mass spectrometry ams at the uppsala tandem laboratory the 36cl measurements in natural samples using a medium sized tandem accelerator 1 mev amu have been considered a gas filled magnetic spectrometer gfm was proposed for the separation of 36cl from its isobar 36s semi empirical monte carlo ion optical calculations were conducted to define optimal conditions for separating 36cl and 36s a 180 gfm was constructed and installed at the dedicated ams beam line 129i has been measured in waters from the arctic and north atlantic oceans most of the 129i currently present in the earth s surface environment can be traced back to liquid and gaseous releases from the nuclear reprocessing facilities at sellafield uk and la hague france the anthropogenic 129i inventory in the central arctic ocean was found to increase proportionally to the integrated 129i releases from these reprocessing facilities the interaction and origin of water masses in the region have been clearly distinguished with the help of 129i labeling predictions based on a compartment model calculation showed that the atlantic ocean and deep arctic ocean are the major sinks for the reprocessed 129i the variability in 129i concentration measured in seawater along a transect from the baltic sea to the north atlantic suggests strong enrichment in the skagerrak kattegat basin the 129i inventory in the baltic and bothnian seas is equal to 0 3 of the total liquid releases from the reprocessing facilities a lake sediment core sampled in northeastern ireland was analyzed for 129i to study the history of the sellafield releases in particular the nuclear accident of 1957 high 129i concentration was observed corresponding to 1990 and later while no indication of the accident was found the results of this thesis research clearly demonstrate the uniqueness and future potential of 129i as a tracer of processes in both marine and continental archives

deep structure and tectonics of the burmese arc constraints from earthquake and gravity data abstract active subduction of the indian plate is currently occurring beneath the burmese arc along an east dipping benioff zone which extends to a depth of about 180 km the overriding burma plate has an appearance of an inland seismic slab that is deflected downwards in the vicinity of the benioff zone a crustal seismic zone some 60 80 km east of the benioff zone correlates to backarc activity a triangular aseismic wedge in the top part of the crust outlines the central belt molasse basin east of the burmese foldbdt fault plane solutions show that the burmese benioff zone is characterized by shallow angle thrusting at its upper edge whereas down tip tensional events dominate its lower edge most of the backarc seismicity is accounted for by the sagaing transform or by the activity of the shan scarp normal fault zone at the margin of the asian plate a gravity anomaly pair with amplitude of 175 mgal coincides with the 1100 km long burmese arc lying in a north south direction the gravity anomalies along a profile in central burma and in adjacent areas of the bengal basin are interpreted in terms of plate subduction as well as near surface mass anomalies this suggests that sediments below the central belt may have an average thickness of the order of 10 km but may be as thick as 15 km at the subduction zone the oceanic crust underlying deeper parts of the bengal basin experiences phase transition at about 30 km depth in a benioff zone environment east of the burmese foldbelt several thrust planes are present within the folded and deformed cretaceous tertiary sediments of the fold belt these are often associated with ophiolites and basic to ultrabasic rocks a low density zone at least 60 km wide underlies the andesitic volcanic axis in the overriding plate

observing global ocean topostrophy 1 recent publications have evaluated topostrophy f v d where is f coriolis v is velocity and d is gradient of total depth as a means of comparing models circulations some results are striking comparing four global models two with modest grid size and two with fine grids merryfield and scott 2007 show that finer grid models are characterized by more positive especially at greater depths and higher latitudes among nine arctic ocean models holloway et al 2007 find in three of the models quite distinct from the other six a result shown to depend upon subgrid eddy parameterization from different choices of numerical method within the same model penduff et al 2007 show that improved numerical representations support more positive can these model results be compared with observations a global compilation has been prepared from 17120 current meter records spanning 83087 current meter months the compilation tends to confirm modeling progress achieved by finer resolution improved parameterizations and better representations a new characterization of global ocean circulation emerges with suggestive dynamical insights

the arctic circumpolar boundary current abstract the main water transformations in the arctic mediterranean take place in the boundary current of atlantic water which crosses the greenland scotland ridge from the north atlantic into the eastern norwegian sea it enters and flows around the arctic ocean before it exits the arctic mediterranean as the east greenland current primarily through denmark strait on route it experiences numerous branchings and mergings by examining how the properties of this circumpolar boundary current evolve it is possible to identify and describe the processes causing the water mass transformations in the arctic mediterranean it is also possible to follow the arctic ocean deep waters as they spread into the nordic seas and eventually provide 40 of the overflow water supplying the north atlantic deep water

iodine 129 cfc 11 transit times for denmark strait overflow water in the labrador and irminger seas 1 iodine 129 discharged from nuclear fuel reprocessing plants in france and the united kingdom is transported into the nordic seas on timescales of 3 5 years tracer 129i is subsequently injected into intermediate waters that overflow the sills between greenland iceland and scotland and ventilate the north atlantic deep waters nadw during the early 1990s discharges of 129i increased by 600 resulting in a large well resolved tracer front whose passage through the nordic seas is presently being observed by a time series of 129i measurements on the woce ar7w section in the labrador sea the highest 129i levels were measured below depths of 3000 m in denmark strait overflow water dsow these levels increased by about 300 between 1997 and 2001 to values 40 107 atoms l indicating that the leading edge of the tracer front from the early 1990s was being observed entering the nadw using a simple mixing advection model 129i and cfc 11 results were used to calculate transit times of 0 4 2 6 years for the flow of dsow from formation regions in the nordic seas to the labrador sea measurements on samples collected in the irminger sea in 2001 gave transit times of 0 3 years for core dsow immediately south of denmark strait and about 2 years for locations off the southern tip of greenland an increase in dsow transit times observed in the labrador sea between 1999 and 2001 probably reflects a more general weakening in the subpolar gyre of the north atlantic during the 1990s