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

simulation of the atlantic circulation with a coupled sea ice mixed layer isopycnal general circulation model part i model description abstract a diabatic ocean general circulation model based on primitive equations is described it uses isopycnals as lagrangian coordinates in the vertical and predicts a free surface prognostic fields of temperature and salinity enter the dynamics as active tracers through a realistic equation of state the surface boundary layer is parameterized by a detailed mixed layer model a sea ice model with a viscous plastic rheology is coupled to the mixed layer thermal forcing wind stress and surface input of turbulent kinetic energy are determined from monthly mean values of atmospheric quantities while the freshwater flux still is parameterized by a newtonian relaxation towards the observed surface salinity the model equations are written in layer formulation each interface represents an isopycnal as the equations are written in flux form the mass flux and the content of mass heat and salt are conserved in the model domain a potential vorticity conserving scheme is included except for the mixed

two circulation regimes of the wind driven arctic ocean the major goal of this paper is to demonstrate the existence in the arctic ocean of two regimes of wind forced circulation we simulated the vertically averaged currents sea level heights and ice drift in the arctic ocean from 1946 to 1993 using a two dimensional wind forced barotropic model that includes frictional coupling between the ocean and ice the model has a spatial resolution of 55 5 km and is driven by winds river runoff and an imposed but realistic sea level slope between the pacific and the atlantic oceans there is a good agreement between velocities from observed buoy motions and velocities of modeled ice drift even though the model lacks ocean baroclinicity and ice thermodynamics the results indicate that wind driven motion in the central arctic alternates between anticyclonic and cyclonic circulation with each regime persisting for 5 7 years based upon our analysis of the modeled sea level and ice motion anticyclonic wind driven motion in the central arctic appeared during 1946 1952 1958 1963 1972 1979 and 1984 1988 and cyclonic motion appeared during 1953 1957 1964 1971 1980 1983 and 1989 1993 shifts from one regime to another are forced by changes in the location and intensity of the icelandic low and the siberian high the two regimes may help explain the significant basin scale changes in the arctic s temperature and salinity structure observed recently the great salinity anomaly and the variability of ice conditions in the arctic ocean

pathways and modification of the upper and intermediate waters of the arctic ocean 1 the purpose of this study is to investigate the pathways and the ventilation of source water masses of the upper and intermediate waters of the arctic ocean for the arctic and subarctic domain a coupled ice ocean general circulation model is set up to be integrated for several decades it is driven by a climatological seasonal cycle of monthly mean atmospheric data from 1980 to 1989 and by restored sea surface salinities passive tracers are used to visualize and interpret the modeled flow and to compare it with observations the model is able to reproduce known features of the arctic ocean circulation like the inflow of two branches of atlantic origin via the fram strait and the barents sea and their subsequent passage at middepths in several cyclonic circulation cells the fate of these atlantic source water masses river water and bering strait inflow water in the model are studied the branch crossing the barents sea is subject to an intense heat loss and ice formation as a result water of this branch leaves the shelf toward the central part of the arctic ocean not only at the surface but also in denser varieties which finally feed the central arctic at halocline and middepths the lightest part turns northward and finally westward joining the transpolar drift the densest part 200 1000 m depth moves eastward along the continental slope a similar path is taken by the atlantic water branch from the fram strait the inflowing branch over the barents sea turns out to be the dominant source for the lower atlantic water layer in the arctic ocean in this investigation atlantic tracers starting in fram strait need 6 years to reach the northern laptev sea slope travel times to return to fram strait are 15 20 years along the lomonossov ridge and about 30 years along the continental slope of the canadian basin tracers that mark the pacific water or the mackenzie river water flow eastward and leave the arctic mainly via the canadian archipelago the siberian river water tracers at the surface penetrate far into the canadian basin before they join the transpolar drift the travel times of the river water from the river mouths are 2 3 years to the shelf edge and 12 14 years to fram strait

freshwater balance and the sources of deep and bottom waters in the arctic ocean inferred from the distribution of h218o data from sections across the eurasian basin of the arctic ocean occupied in 1987 and 1991 are used to derive information on the freshwater balance of the arctic ocean and on sources of the deep waters of the nansen amundsen and makarov basins using salinity h218o and mass balances we estimate the river runoff and the sea ice melt water fractions contained in the upper waters of the arctic ocean and infer pathways of the river runoff signal from the shelf seas across the central arctic ocean to fram strait the average mean residence time of the river runoff fraction contained in the arctic ocean halocline is determined to be about 11 to 14 years pacific water entering through bering strait is traced using silicate and its influence on the halocline waters of the canadian basin is estimated water column inventories of river runoff and sea ice melt water are calculated for a section just north of fram strait and implications of these inventories for sea ice export through fram strait are discussed comparison of the 18o 16o ratios of shelf water atlantic water and the deep waters of the arctic ocean indicate that the sources of the deep and bottom waters of the eurasian basin are located in the barents and kara seas

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

on the dynamics of atlantic water circulation in the arctic ocean 1 we use a subset of models from the coordinated experiment of the arctic ocean model intercomparison project aomip to analyze differences in intensity and sense of rotation of atlantic water circulation we focus on the interpretation of the potential vorticity pv balance results differ drastically for the eurasian and the amerasian basins of the arctic ocean we find indications that in the eurasian basin the lateral net flux of pv is a significant factor for the determination of the sense of rotation of atlantic water circulation on timescales beyond pentades the main source of high pv causing cyclonic circulation in the eurasian basin is the barents sea where the seasonal cycle of surface buoyancy fluxes forms stratified water that leaves the shelf and feeds the atlantic water layer awl in the arctic basins however in the amerasian basin vertical pv fluxes are the more important factor these are closely related to wind field changes we find an intense response of the awl flow to wind forcing approximated by the sea level pressure difference between the bering sea and the central canadian basin which describes about half the variance of awl flow of the amerasian basin an experiment driven with a repeated atmospheric climatology exhibits an extreme case where a permanent high pressure system over the beaufort sea dominates the circulation in the amerasian basin demonstrating the potential of the beaufort gyre to adjust in such a way as to suppress a cyclonic awl flow in the amerasian basin in more realistic cases the beaufort gyre still modulates the amerasian basin awl circulation significantly

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

the profile of the rare earth elements in the canada basin arctic ocean we analyzed the dissolved rare earth element ree content of three water column profiles two shelf sites and one deep basin site in the canada basin in order to better constrain the behavior of rees in the arctic ocean dissolved concentrations of the rees in the surface are 1 3 to 1 9 times higher than deep water 500 m concentrations which are constant with depth la 19 23 pm nd 14 17 pm yb 4 0 4 3 pm the dominant source of rees to the surface waters of the canada basin is most likely pacific water flowing through the bering strait and chukchi sea and or the mackenzie river dissolved rees in the intermediate and deep waters are constant and appear to behave conservatively allowing us to investigate this aspect of ree behavior in the oceans calculated deep ocean residence times of the rees in the canada basin range from 450 700 years and match the age of these waters we postulate that these values are likely applicable to global deep ocean reservoirs and that observed deviations from this conservative value can help to constrain non conservative processes acting on the rees this article is protected by copyright all rights reserved

renewal and circulation of intermediate waters in the canadian basin observed on the scicex 96 cruise during the summer of 1996 the nuclear submarine uss pogy occupied a line of stations extending through the middle of the canadian basin between about 88 n 44 w lomonosov ridge and about 78 n 144 w center of the canada basin ctd niskin bottle casts extending to 1600 m were carried out at eight stations providing the first high quality temperature salinity cfc tritium and 3he data obtained from this region although xctd data had previously been collected in this region these data along with data from stations at the basin boundary to the south and west reveal the presence of well ventilated intermediate water beneath the halocline in the center of the canada basin indicating renewal times of the order of 1 2 decades the least ventilated intermediate water was observed at the northern end of the canada basin along the southern flank of the alpha ridge intermediate water is derived from the atlantic ocean and enters the arctic ocean through fram strait and the barents sea it flows around the arctic basins in boundary currents and splits in the eastern amundsen basin with one branch crossing the lomonosov ridge and flowing along the east siberian continental slope and the other flowing along the eurasian flank of the lomonosov ridge from the 1996 scientific ice expedition scicex 96 observations we conclude that the branch that flows along the east siberian continental slope transports this water to the chukchi rise where it apparently enters the central canada basin with some flow continuing along the boundary to the southern canada basin the fram strait branch water mixes extensively with waters from the canadian basin during its transit along the east siberian continental slope being diluted by a factor of about 5 by the time it reaches the central canada basin the barents sea branch water does not undergo such extensive mixing and is diluted by a factor of only about 2 when it reaches the central canada basin

ventilation of the arctic ocean estimated by a plume entrainment model constrained by cfcs intermediate and deep water formation rates in the arctic ocean are estimated using a plume entrainment model based on shelf slope processes and constrained by tracer distributions within the deep basin each plume is initiated by a fraction rj leaving the shelf break at 200 m followed by an entrainment of rj for every 150 m depth the plume descends the model is tuned by varying rj to achieve the transient tracer cfc 12 and carbon tetrachloride distribution as measured in the nansen amundsen and makarov basins during the oden 1991 expedition and the concentrations in the source waters are calculated assuming a water in 100 equilibrium with the atmosphere the formation of water entering below 500 m is computed to be 1 5 and 1 9 sv when constrained by cfc 12 and ccl4 respectively with a total uncertainty of 0 45 sv sensitivities of the model settings to the entrainment rate degree of saturation of the transient tracer in the source waters and age of the atlantic layer water are investigated processes in the arctic ocean contribute around 1 3 of the approximately 5 6 sv that flows over the scotland greenland ridge with the rest likely attributed processes in the greenland and iceland seas we thus conclude that the arctic ocean has to be included in the discussion of the sensitivity of the greenland scotland overflow to a climate change

monitoring ice thickness in fram strait time series of ice thickness in fram strait are evaluated together with ice drift for estimation of the ice flux from the arctic ocean ice draft was measured from moored sonars every 4 min suggesting a nominal sampling interval of 30 m on the basis of these data the annual cycle of many statistics can be resolved the modal ice thickness shows a maximum of 3 15 m in may and a minimum in september of 2 43 m indicating an annual variation range of 0 72 m this compares with model results comprehensive drillings and most of the submarine observations during the last 2 3 decades indicating no significant long term ice thickness change this is also concurrent with the lack of significant temperature changes in the arctic ocean during the same period the mean ice thickness in the central core of the ice stream shows an annual amplitude of 1 m with a minimum in september of 2 25 m and a maximum in april may of 3 25 m the mean thickness of ice only open water excluded is 3 27 m and compares with 3 29 m which is the mean thickness of ice only from 17 submarine tracks in the arctic ocean 1960 1982 the mean annual ice export which is equal to the mean annual net production of ice in the arctic ocean is 2850 km 3 yr 1 for the period 1990 1996 this efflux shows significant variations from year to year with a minimum in 1990 1991 of 2050 km 3 yr 1 and a maximum in 1994 1995 of 4700 km 3 yr 1 this significant variation of nearly 130 is mainly caused by an increased atmospheric forcing and to a lesser degree by an increase in the annual mean ice thickness of 20 over the same period

seabed erosion on the lomonosov ridge central arctic ocean a tale of deep draft icebergs in the eurasia basin and the influence of atlantic water inflow on iceberg motion 1 the submarine lomonosov ridge which bisects the arctic ocean is covered by 450 m of hemipelagic sediments high resolution chirp sonar and side scan data have documented erosion of a section of the ridge here we present multichannel seismic and chirp sonar data which show removal of unconsolidated sediments along the eurasia basin side of the lomonosov ridge where the central ridge is shallower than 1000 m the incomplete erosion of the hemipelagic drape and probable topographic control of ice motion suggest that the deepest draft glacier ice which reached the central arctic ocean from the eurasia basin was in the form of armadas of large icebergs embedded in sea ice rather than a single continuous floating ice shelf massive rapid discharge of glacier ice was probably required to produce the deepest draft 800 m icebergs eastward and northward drift trajectories from a likely iceberg source area on the kara barents sea margin would reflect the relative strength of atlantic inflow through the fram strait however only icebergs with drafts exceeding bathymetric thresholds on the lomonosov ridge would leave an erosive imprint on the seabed advection of atlantic water may have been relatively strong at times of discharge from the saalian ice sheet icebergs exiting the arctic ocean caused massive erosion and redeposition of the hemipelagic sediments on top of yermak plateau

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

palaeomagnetism and u pb dates of the palaeoproterozoic akitkan group south siberia and implications for pre neoproterozoic tectonics

variations of north atlantic inflow to the central arctic ocean over the last 14 million years inferred from hafnium and neodymium isotopes the warm and saline north atlantic inflow to the arctic ocean is a major component of high northern latitude circulation and the main mechanism of deep water renewal in the arctic ocean knowledge of its past variability is critical for understanding the high latitude feedback mechanisms of the climate system here we present the first combined seawater hf and nd isotope compositions of past arctic intermediate water extracted from the authigenic fe mn oxyhydroxide fraction of two sediment cores recovered near the north pole to reconstruct changes in contributions from glacial brines of the eurasian shelf and past inflow of atlantic waters the hf and nd isotopic compositions obtained from leachates of the authigenic fraction show closely coupled and environmentally controlled variations over the past 14 million years an observed offset of these data from seawater ehf and end compositions from other ocean basins seawater array is interpreted as the result of continuously prevailing glacial weathering conditions on the high latitude eurasian continent in the late quaternary large amplitude hf and nd isotopic variations of arctic intermediate water aiw was characterized by more radiogenic isotope signatures generally prevailing under glacial conditions and less radiogenic values during interglacial periods on the basis of the close coupling between nd and hf isotopes we suggest that the evolution of hf isotope compositions of central arctic aiw has primarily been controlled by changes in ocean circulation and provenance of weathering inputs rather than changes in weathering regime

variations in architecture and cyclicity in fault bounded carbonate platforms early miocene red sea rift nw saudi arabia abstract the early miocene was a period of active rifting and carbonate platform development in the midyan peninsula nw saudi arabia however there is no published literature available dealing with the detailed characterization of the different carbonate platforms in this study area therefore this study aims to present new stratigraphic architectural models that illustrate the formation of different carbonate platforms in the region and the forcing mechanisms that likely drove their formation this study identified the following features formed during active rifting a a late aquitanian n4 fault block hangingwall dipslope carbonate ramp b a late burdigalian n7 n8 isolated normal fault controlled carbonate platform with associated slope deposits and c a late burdigalian n7 n8 attached fault bounded platform with reef buildups rimmed shelf developed on a footwall fault tip within a basin margin structural relay zone that formed coinciding with the second stage of rifting variations in cyclicity have been observed within the internal stratigraphic architecture of each platform and also between platforms high resolution sequence stratigraphic analysis shows to be parasequences the smallest depositional packages metre scale cycles within the platforms the hangingwall dipslope carbonate ramp and the attached platform demonstrate aggradational progradational parasequence stacking patterns these locations appear to have been more sensitive to eustatic cyclicities despite the active tectonic setting the isolated fault controlled carbonate platform reveals disorganized stratal geometries in both platform top and slope facies suggesting a more complex interplay of rates of tectonic uplift and subsidence variation in carbonate productivity and resedimentation of carbonates such that any sea level cyclicity is obscure this study explores the interplay between different forcing mechanisms in the evolution of carbonate platforms in active extensional tectonic regions characterization of detailed parasequence scale internal architecture allows the spatial variation in syn depositional relative base level changes to be inferred and is critical for understanding the development of rift basin carbonate platforms such concepts may be useful for the prediction of subsurface facies relationships beyond interwell areas in hydrocarbon exploration and reservoir modeling activities

on the origins of water masses exported along both sides of greenland a lagrangian model analysis the origin of the water masses exported from the arctic to the north atlantic along both sides of greenland is investigated using an original numerical method a quantitative lagrangian analysis is applied to the monthly climatological 3 d output of a global ocean sea ice high resolution model it allows quantification of the different branches of the export to the north atlantic as well as related timescales and water mass transformations in the model the outflow through davis strait consists in equal parts of pacific and atlantic water whilst the export through fram strait consists almost fully of atlantic water contrary to observations pacific water is transferred quickly o 10 years to the north atlantic through the beaufort gyre where gradual warming and salinification occur atlantic water exiting in the surface layer along both sides of greenland remains about 10 years in the arctic basin and undergoes cooling and significant freshening below the surface water atlantic water exiting through the intermediate and deep layers in fram strait follows different pathways in the arctic with trajectories being subject to topography constraints the travel time depends strongly on the pathway from 1 to 1000 years the intermediate outflow consists mainly of water entering the arctic at fram strait while half the deep outflow is composed of water from the barents sea we find that the barents sea branch which contributes to both the outflows at fram and davis straits is almost fully transformed after a year due to heat exchanges with the very cold atmosphere in the barents sea

plio pleistocene evolution of water mass exchange and erosional input at the atlantic arctic gateway water mass exchange between the arctic ocean and the norwegian greenland seas has played an important role for the atlantic thermohaline circulation and northern hemisphere climate we reconstruct past water mass mixing and erosional inputs from the radiogenic isotope compositions of neodymium nd lead pb and strontium sr at ocean drilling program site 911 leg 151 from 906 m water depth on yermak plateau in the fram strait over the past 5 2 myr the isotopic compositions of past bottom waters were extracted from authigenic oxyhydroxide coatings of the bulk sediments neodymium isotope signatures obtained from surface sediments agree well with present day deepwater end signature of 11 0 0 2 prior to 2 7 ma the nd and pb isotope compositions of the bottom waters only show small variations indicative of a consistent influence of atlantic waters since the major intensification of the northern hemisphere glaciation at 2 7 ma the seawater nd isotope composition has varied more pronouncedly due to changes in weathering inputs related to the waxing and waning of the ice sheets on svalbard the barents sea and the eurasian shelf due to changes in water mass exchange and due to the increasing supply of ice rafted debris ird originating from the arctic ocean the seawater pb isotope record also exhibits a higher short term variability after 2 7 ma but there is also a trend toward more radiogenic values which reflects a combination of changes in input sources and enhanced incongruent weathering inputs of pb released from freshly eroded old continental rocks

the western arctic boundary current at 152 w structure variability and transport abstract from august 2002 to september 2004 a high resolution mooring array was maintained across the western arctic boundary current in the beaufort sea north of alaska the array consisted of profiling instrumentation providing a timeseries of vertical sections of the current here we present the first year velocity measurements with emphasis on the pacific water component of the current the mean flow is characterized as a bottom intensified jet of o 15 cm s 1 directed to the east trapped to the shelfbreak near 100 m depth its width scale is only 10 15 km seasonally the flow has distinct configurations during summer it becomes surface intensified as it advects buoyant alaskan coastal water in fall and winter the current often reverses flows westward under upwelling favorable winds between the storms as the eastward flow re establishes the current develops a deep extension to depths exceeding 700 m in spring the bottom trapped flow advects winter transformed pacific water emanating from the chukchi sea the year long mean volume transport of pacific water is 0 13 0 08 sv to the east which is less than 20 of the long term mean bering strait inflow this implies that most of the pacific water entering the arctic goes elsewhere contrary to expected dynamics and previous modeling results possible reasons for this are discussed the mean atlantic water transport to 800 m depth is 0 047 0 026 sv also smaller than anticipated

on large scale shifts in the arctic ocean and sea ice conditions during 1979 98 results from a regional model of the arctic ocean and sea ice forced with realistic atmospheric data are analyzed to understand recent climate variability in the region the primary simulation uses daily averaged 1979 atmospheric fields repeated for 20 years and then continues with interannual forcing derived from the european centre for medium range weather forecasts for 1979 98 an eastward shift in the ice ocean circu lation fresh water distribution and atlantic water extent has been determined by compar ing conditions between the early 1980s and 1990s a new trend is modeled in the late 1990s and has a tendency to return the large scale sea ice and upper ocean conditions to their state in the early 1980s both the sea ice and the upper ocean circulation as well as fresh water export from the russian shelves and atlantic water recirculation within the eurasian basin indicate that the arctic climate is undergoing another shift this suggests an oscillatory behavior of the arctic ocean system interannual atmospheric variability appears to be the main and sufficient driver of simulated changes the ice cover acts as an effective dy namic medium for vorticity transfer from the atmosphere into the ocean

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

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

the tracing of riverine u in arctic seawater with very precise 234u 238u measurements abstract the riverine flux of u that enters the deep oceans is not well constrained since the net losses during estuarine mixing are difficult to quantify riverine dissolved u normally has a higher 234 u 238 u activity ratio 234 u 238 u ar than the uniform value that characterizes open ocean seawater and could be used as a tracer of riverine inputs if one could resolve subtle variations in seawater composition using new mass spectrometry techniques we achieve a long term reproducibility 0 3 on 234 u 238 u ar which permits the tracing of riverine u in seawater samples from the arctic a partially restricted basin that is ideal for such a study we find that surface waters from the arctic basins carry elevated 234 u 238 u ar when compared with deep ocean seawater samples from the canada basin have a significant freshwater component and provide evidence that the mackenzie river loses 65 of its u in the mackenzie shelf estuary zone before entering the deeper basin this is in contrast to samples from the makarov basin which provide evidence that all of the freshwater input is derived from the major yenisey river alone despite the proximity of the lena and ob rivers the differing behaviour of u between the mackenzie and yenisey rivers is most likely a consequence of the strong binding of u to dissolved organic matter doc or secondary phases in these rivers the yenisey river appears to transport the majority of the doc through the shelf and into the makarov basin in contrast the mackenzie river appears to lose a significant amount of doc 50 in the estuary shelf zone which may lead to loss of associated u these findings offer a more detailed picture of the fresh riverine water flow patterns in the arctic ocean when compared to other geochemical proxies the non conservative behaviour of u in the mackenzie river through the shelf estuaries has important implications for u input into oceans and the total marine budget

on improving the simulation of atlantic water circulation in the arctic ocean 1 we performed a set of numerical experiments in order to better simulate the circulation of atlantic water in the arctic ocean by employing a coupled ice ocean arctic regional model we found that the inflow of atlantic water via fram strait is weak in the case of high viscosity and diffusivity coefficients 1 108 cm2 s and 1 107 cm2 s and creates an anticyclonic circulation in the eurasian basin this flow increases significantly when both coefficients are scaled down to 1 107 cm2 s and 0 5 106 cm2 s but the current path is then unstable and it becomes mostly anticyclonic after about a decade of integration a further reduction of these coefficients leads to growing instabilities due to insufficient grid resolution short term integration of the model with doubled space resolution shows better agreement with observations but long term calculation is still restricted by simulation time alternatively a lower resolution version of this model benefits from parameterizations of subscale processes incorporation of the neptune parameterization of eddy topography interaction into the model intensifies the current steered by subsurface topography and results in cyclonic circulation of the atlantic water in every subbasin and in the whole arctic region in the absence of salinity restoring there was strong salinity drift at the surface resulting in a salinity increase in the central arctic by 3 units from 1960 to 2005 the arctic freshwater content is driven basically by year to year variations of convective mixing involving more saline water from lower layers after cooling and increasing in salinity through brine rejection the surface water becomes denser leading to even stronger convective mixing one dimensional model tests showed how model performance could be improved by implementing a lower vertical diffusion coefficient and higher vertical resolution

circulation features in the central arctic ocean revealed by nuclear fuel reprocessing tracers from scientific ice expeditions 1995 and 1996 measurements of the tracer radionuclides 129 i and 137 cs were conducted on seawater samples collected during the scientific ice expedition cruises to the arctic ocean of the u s navy nuclear submarines uss cavalla and uss pogy in 1995 and 1996 respectively these radionuclides are derived mainly from discharges from the sellafield england united kingdom and la hague france nuclear fuel reprocessing plants and are subsequently transported with atlantic water into the arctic ocean through fram strait and the barents sea iodine 129 results from halocline waters water depths of 59 and 134 m collected virtually synoptically throughout the central arctic ocean during the uss cavalla cruise clearly show the front between atlantic origin water having high 129 i levels 100 10 7 atoms l 1 and pacific origin water labeled mainly by fallout 30 10 7 atoms l 1 measured in central regions of the canada basin indicate that the interior is more efficiently ventilated than previously thought possibly by separation from boundary currents flowing over the continental margin north of the chukchi plateau the 129 i and 137 cs data were interpreted using a transit time model that provided estimates of 6 7 years 0 5 years for the passage of halocline and atlantic water from the norwegian coastal current 60 n to the continental slope of the makarov basin and a lower limit of 8 years for transport to interior regions of the makarov and amundsen basins

investigation of subsurface water flow along the continental margin of the eurasian basin using the transient tracers tritium 3he and cfcs during august september 1993 the r v polarstern expedition ark ix 4 was made to the eurasian continental margin of the arctic ocean sections of oceanographic stations leading from the outer shelf over the continental slopes toward the deep eurasian basin were occupied north of the barents and laptev seas the distributions of the transient tracers cfc 11 cfc 12 tritium and 3he were measured along these sections and are discussed in relation to water mass distribution and circulation along the continental margin of the eurasian basin the tracer data strongly corroborate the temperature and salinity data schauer et al 1997 clearly showing the inflow of atlantic water in two branches the fram strait branch and the barents sea branch high cfc and tritium concen trations extended down to 1300 m over the laptev continental slope indicating strong inflow of the barents sea branch between franz josef land and severnaya zemlya the apparent ages of water in the fram strait branch were estimated to be about 2 years north of the barents sea and 6 years at the eastern end of the nansen basin which corresponds to an apparent mean current speed of about 1 cm s 1 the age of the core of the barents sea branch was also estimated to be about 6 years over the laptev slope region and to increase by 0 5 years as it flowed through this region a lower limit for the inflow of newly formed barents sea branch water was estimated to be 0 5 sv and an overall transport for the sum of fram strait branch plus barents sea branch flow of 4 sv was estimated from this aging in the deep water there was clear evidence for the inflow of norwegian sea deep water through fram strait but there appeared to be no significant input of shelf derived water from the santa anna trough if there was any shelf derived input to eurasian basin bottom water it entered at a deeper depth than was sampled on the slope sections in the laptev sea or its flow is intermittent and was not occurring during the ark ix 4 expedition

deep arctic ocean warming during the last glacial cycle in the arctic ocean the cold and relatively fresh water beneath the sea ice is separated from the underlying warmer and saltier atlantic layer by a halocline ongoing sea ice loss and warming in t

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

observed winter salinity fields in the surface layer of the arctic ocean and statistical approaches to predicting large scale anomalies and patterns significant salinity anomalies have been observed in the arctic ocean surface layer during the last decade our study is based on an extensive gridded dataset of winter salinity in the upper 50 m layer of the arctic ocean for the periods 1950 1993 and 2007 2012 obtained from 20 000 profiles we investigate the interannual variability of the salinity fields identify predominant patterns of anomalous behavior and leading modes of variability and develop a statistical model for the prediction of surface layer salinity the statistical model is based on linear regression equations linking the principal components of surface layer salinity obtained through empirical orthogonal function decomposition with environmental factors such as atmospheric circulation river runoff ice processes and water exchange with neighboring oceans using this model we obtain prognostic fields of the surface layer salinity for the winter period 2013 2014 the prognostic fields generated by the model show tendencies of surface layer salinification which were also observed in previous years although the used data are proprietary and have gaps they provide the most spatiotemporally detailed observational resource for studying multidecadal variations in basin wide arctic salinity thus there is community value in the identification dissemination and modeling of the principal modes of variability in this salinity record

barium as a tracer of arctic halocline and river waters dissolved barium ba concentrations are reported for water samples collected during six oceanographic cruises to the arctic in 1993 and during the 1994 arctic ocean section upper arctic 75 nmol ba 1 1 observed in the surface mixed layer of the arctic interior i e beyond the 200 m isobath occurred in the canada basin as a result of the biological removal of ba from surface waters of the chukchi sea and the tendency of the bering inflow to enter the arctic interior at depths below the relatively fresher mixed layer we hypothesize that the mackenzie river is the dominant source of the high ba observed in the surface waters of the canada basin features characterized by local salinity minima and ba maxima in surface waters down to depths of 30 50 m were observed over the arlis plateau and mendeleyev ridge in both 1993 and 1994 and over the makarov basin and lomonosov ridge in 1994 the physical and chemical properties of these waters suggest that they have been significantly influenced by fluvial discharge it could not be determined from available data whether these features arose from offshore transport of eurasian river discharge from the russian arctic seas meanders of the mackenzie river influenced beaufort gyre or a branch of bering inflow that crossed the chukchi shelf and entrained river water from north american and or eurasian sources in both 1993 and 1994 ba concentrations in the upper halocline layer as defined by a core salinity of 33 1 ranged between 42 and 77 nmol ba 1 1 with highest values observed in the canada basin the ba maximum and the related nutrient maxima and oxygen minimum that characterize the upper halocline in the canada basin suggest sources in the chukchi and beaufort seas and that the mechanism by which these waters are formed is linked with the influx of water through the bering strait the ba distributions for 1993 and 1994 delineate the lateral extent of upper halocline waters with canada basin character and show them to be chemically distinct from upper halocline waters in the eurasian basin the front separating these water types ran roughly along the mendeleyev and alpha ridges consistent with reports that the boundary between atlantic and pacific water mass assemblies in the arctic has recently been displaced from its historical position over the lomonosov ridge lateral gradients in both ba and the no parameter were observed within the lower halocline layer defined by an no minimum and core salinity of 34 2 34 4 along the 1994 arctic ocean section indicating that lower halocline waters receive additional inputs as they transit to the canadian basin from their region of formation in the eurasian sector of the arctic

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

simulation of the mixed layer circulation in the arctic ocean a numerical simulation of the mixed layer circulation of the arctic ocean is presented using oberhuber s 1993a coupled sea ice mixed layer isopycnal ocean general circulation model the model domain includes the arctic ocean and the greenland iceland norwegian gin sea the horizontal resolution is 2 the vertical is resolved using five isopycnal layers of which the uppermost layer is a turbulent mixed layer the sea ice is modeled using a thermodynamic dynamic model which includes a viscous plastic rheology monthly climatological atmospheric forcing is used to spin up the model into a cyclostationary equilibrium model results are presented and discussed with respect to observational and previous modeling studies the mixed layer shows a circulation pattern similar to that inferred from indirect observations and other modeling studies in an attempt to determine the main driving mechanism for the mixed layer circulation as produced by the oberhuber model a set of sensitivity experiments is carried out in particular the relative importance of 1 ice cover 2 atmospheric winds 3 surface freshwater fluxes and 4 initialization with levitus 1982 data is examined to determine the contribution each makes to the modeled circulation the key conclusion is that buoyancy forcing is critical to maintaining the mixed layer circulation

seasonal variability of water mass distribution in the southeastern beaufort sea determined by total alkalinity and δ18o 1 we examined the seasonal variability of water mass distributions in the southeastern beaufort sea from data collected between september 2003 and august 2004 salinity total alkalinity ta and isotopic composition 18o of seawater were used together as tracers of freshwater input i e meteoric water and sea ice meltwater we used an optimum multiparameter analysis to identify the different water masses including the mackenzie river sea ice melt sim winter polar mixed layer pml upper halocline water uhw with core salinity of 33 1 psu pacific origin and atlantic water computed values of co2 fugacity in seawater fco2 sw show that the surface mixed layer sml remains mostly undersaturated 328 55 atm n 552 with respect to the average atmospheric co2 concentration 380 5 atm over the study period the influence of the mackenzie river fco2 sw 500 atm was relatively small in the southeastern beaufort sea and significant fractions were only observed on the inner mackenzie shelf the contribution of sea ice melt fco2 sw 600 atm was usually located between 120 and 180 m depth but could contribute to the sml during wind driven upwelling events in summer and autumn and during brine driven eddies in winter

circulation in the arctic ocean results from a high resolution coupled ice sea nested global fvcom and arctic fvcom system abstract a high resolution unstructured grid global regional nested ice current coupled fvcom system was configured for the arctic ocean and used to examine the impact of model resolution and geometrical fitting on the basin coastal scale circulation and transport in the pan arctic with resolving steep bottom slope and irregular coastal geometry the model was capable of simulating the multi scale circulation and its spatial variability in the arctic basin and flow through the bering strait fram strait and canadian archipelago the model simulated annual mean velocities were in good agreement with observations within the measurement uncertainty and variability due to insufficient sampling the errors in the flow direction varied with the flow speed larger in the weak velocity zone and smaller as the velocity increased in the upper 50 m layer the annual mean circulation pattern was dominated by the wind and ice drifting induced anticyclonic circulation in the arctic basin and a relatively strong cyclonic slope current along the edge of the continental shelf in the deep 200 600 m layer a relatively permanent cyclonic circulation occurred along the steep bottom slope these annual mean circulations accounted for 85 of the total kinetic energy variance de trending the mean flow an empirical orthogonal function eof analysis showed that the semi annual and seasonal variability of the sub tidal flow was dominated by the first and second modes that accounted for 46 and 30 of the total variance in the upper 50 m layer and 58 and 20 in the deep 200 600 m layer consistent with observations the ao fvcom simulated cyclonic slope flow was characterized by a large positive topostrophy sensitivity experiment results with various grid configurations suggested that the currents over slopes narrow straits and water passages featured topographic and baroclinic frontal dynamical scales associated with bathymetric slope and internal rossby deformation radius over the arctic slope since these two scales are in the same order the along slope current could be captured as the cross isobath model resolution was refined to resolve the steep bottom topography under this condition there is no need to add neptune forcing into the momentum equations the accuracy of the estimation of the transport through the strait and narrow water passage was affected by the model resolution in fram strait where the flow is characterized by strong lateral current shear resulting from the atlantic inflow and arctic outflow the transport estimation could have a significant uncertainty due to both horizontal and vertical sampling resolutions

the dissolved beryllium isotope composition of the arctic ocean we present the first comprehensive set of dissolved 10 be and 9 be concentrations in surface waters and vertical profiles of all major sub basins of the arctic ocean which are complemented by data from the major arctic rivers mackenzie lena yenisey and ob the results show that 10 be and 9 be concentrations in waters below 150 m depth are low and only vary within a factor of 2 throughout the arctic basin 350 750 atoms g and 9 15 pmol kg respectively in marked contrast be isotope compositions in the upper 150 m are highly variable and show systematic variations cosmogenic 10 be concentrations range from 150 to 1000 atoms g and concentrations of terrigenous 9 be range from 7 to 65 pmol kg resulting in 10 be 9 be ratios atom atom between 0 5 and 14 10 8 inflowing atlantic water masses in the eurasian basin are characterized by a 10 be 9 be signature of 7 10 8 the inflow of pacific water masses across the bering strait is characterized by lower ratios of 2 3 10 8 which can be traced into the central arctic ocean possibly as far as the fram strait a comparison of the high dissolved surface 10 be and 9 be concentrations corresponding to low 10 be 9 be signatures of 2 10 8 in the eurasian basin with hydrographic parameters and river data documents efficient and rapid transport of be with siberian river waters across the siberian arctic shelves into the central arctic basin although significant loss and exchange of be on the shelves occurs in contrast fresh surface waters from the canada basin also show high cosmogenic 10 be contents but are not enriched in terrigenous 9 be resulting in high 10 be 9 be signatures of up to 14 10 8 this is explained by a combination of efficient scavenging of be in the mackenzie river estuary and the shelves and additional supply of cosmogenic 10 be via atmospheric fallout and melting of old sea ice the residence time of be in the deep arctic ocean estimated from our data is 800 years and thus similar to the average be residence time in the global ocean 2009 elsevier ltd all rights reserved

influence of brine formation on arctic ocean circulation over the past 15 million years the early oceanographic history of the arctic ocean is important in regulating and responding to climatic changes however constraints on its oceanographic history preceding the quaternary the past 1 8 myr have become available only recently because of the difficulties associated with obtaining continuous sediment records in such a hostile setting here we use the neodymium isotope compositions of two sediment cores recovered near the north pole to reconstruct over the past approx15 myr the sources contributing to arctic intermediate water a water mass found today at depths of 200 to 1 500 m we interpret high neodymium ratios for the period between 15 and 2 myr ago and for the glacial periods thereafter as indicative of weathering input from the siberian putoranan basalts into the arctic ocean arctic intermediate water was then derived from brine formation in the eurasian shelf regions with only a limited contribution of intermediate water from the north atlantic in contrast the modern circulation pattern with relatively high contributions of north atlantic intermediate water and negligible input from brine formation exhibits low neodymium isotope ratios and is typical for the interglacial periods of the past 2 myr we suggest that changes in climatic conditions and the tectonic setting were responsible for switches between these two modes