water geochemistry of the chaohu lake basin rivers china chemical weathering and anthropogenic inputs abstract as one of the five largest freshwater lakes in china the chaohu lake is polluted by many kinds of pollutants chemical and sr isotopic compositions of river waters in the zhegao river sub catchment have been determined with the main purpose of understanding the contribution of chemical weathering and anthropogenic inputs to solutes the major ion compositions of the river waters are characterized by the dominance of ca2 and hco 3 followed by mg2 and so 4 2 the chemical and sr isotopic analyses indicate that three major reservoirs carbonate silicate and human activities contribute to the dissolved load the calculated results show that the dissolved load is dominated by carbonate weathering the contribution of the anthropogenic inputs is estimated to be from 1 64 to 31 8 with an average of 15 6 demonstrating the strong impacts of human activities on water chemistry the total chemical denudation flux of the zhegao sub catchment is about 127 7 ton km 2 a 1 with carbonate and silicate weathering rates of 97 5 ton km 2 a 1 and 30 2 ton km 2 a 1 respectively

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

the atlantic water boundary current north of svalbard in late summer data from a shipboard hydrographic velocity survey carried out in september 2013 of the region north of svalbard in the nansen basin are analyzed to characterize the atlantic water aw boundary current as it flows eastward along the continental slope eight meridional transects across the current spanning an alongstream distance of 180 km allow for a detailed description of the current and the regional water masses during the survey the winds were light and there was no pack ice the mean section reveals that the boundary current was o 40 km wide surface intensified with a maximum velocity of 20 cm s its mean transport during the survey was 3 11 0 33 sv of which 2 31 0 29 sv was aw this suggests that the two branches of aw entering the arctic ocean via fram strait the yermak plateau branch and the svalbard branch have largely combined into a single current by 30 e at this location the boundary current meanders with a systematic change in its kinematic structure during offshore excursions a potential vorticity analysis indicates that the flow is baroclinically unstable consistent with previous observations of aw anticyclones offshore of the current as well as the presence of a near field cyclone in this data set our survey indicates that only a small portion of the boundary current is diverted into the kvitoya trough 0 17 0 08 sv and that the aw temperature salinity signal is quickly eroded within the trough

the arctic and subarctic ocean flux of potential vorticity and the arctic ocean circulation according to observations the arctic ocean circulation beneath a shallow thermocline can be schematized by cyclonic rim currents along shelves and over ridges in each deep basin the circulation is also believed to be cyclonic this circulation pattern has been used as an important benchmark for validating arctic ocean models however modeling this grand circulation pattern with some of the most sophisticated ocean ice models has been often difficult the most puzzling and thus perhaps the most interesting finding from the arctic ocean model intercomparison project aomip an international consortium that runs 14 arctic ocean models by using the identical forcing fields is that its model results can be grouped into two nearly exact opposite patterns while some models produce cyclonic circulation patterns similar to observations others do the opposite this study examines what could be possibly responsible for such strange inconsistency it is found here that the flux of potential vorticity pv from the subarctic oceans strongly controls the circulation directions for a semienclosed basin like the arctic the pv integral over the whole basin yields a balance between the net lateral pv inflow and the pv dissipation along the boundary when an isopycnal layer receives a net positive pv through inflow outflow the circulation becomes cyclonic so that friction can generate a flux of negative pv to satisfy the integral balance for simplicity a barotropic ocean model is used in this paper but its application to the 3d models will be discussed in the first set of experiments the model with a realistic arctic bathymetry is forced by observed inflows and outflows in this case there is a net positive pv inflow to the basin due to the fact that inflow layer is thinner than that of outflow the model produces a circulation field that is remarkably similar to the one from observations in the second experiment the model bathymetry at fram strait is modified so that the same inflows and outflows of water masses lead to a net negative pv flux into the arctic the circulation is reversed and becomes nearly the opposite of the first experiment in the third experime nt the net pv flux is made to be zero by modifying again the sill depth at fram strait the circulation becomes two gyres a cyclonic one in the eurasian basin and an anticyclonic one in the canada basin to elucidate the control of the pv integral a second set of model experiments is conducted by using an idealized arctic bathymetry so that the pv dynamics can be better explained without the complication of rough topography the results from five additional experiments that used the idealized topography will be discussed while the model used in this study is one layer the same pv integral constraint can be applied to any isopycnal layer in a threedimensional model variables that affect the pv fluxes to this density layer at any inflow outflow channel such as layer thickness and water volume flux can affect the circulation pattern the relevance to 3d models is discussed in this paper

frontogenesis subduction and cross front exchange at upper ocean fronts the subduction of water at upper ocean fronts driven by internal instabilities is investigated a simple analytic model which assumes conservation of potential density and potential vorticity is used to characterize the expected structure of subducted parcels as a function of the surface layer depth and the length scale of the parcel parcels subducted from a deep surface layer will be characterized by anomalously low potential vorticity and anticyclonic circulation while shallow surface layers result in subducted parcels with high potential vorticity and cyclonic circulation a nonlinear isopycnal primitive equation model is used to demonstrate how baroclinic instability and the resulting frontogenesis force the subduction of parcels below and across the front frontogenesis generates vertical velocities of 0 30 m d and ageostrophic cross front flows of 3 to 5 cm s the subduction is achieved by the deep ageostrophic flow which carries water from the surface layer below and across the front the subducted parcels quickly develop a circulation through balanced adjustment anticyclonic for deep surface layers and cyclonic for shallow surface layers the characteristics of parcels subducted in winter conditions closely resemble a class of eddies called submesoscale coherent vortices the horizontal and vertical scales of the vortices are determined by the frontogenetic mechanism and the depth of the surface layer the total permanent subduction rate is estimated to be 20 m yr for frontal subduction driven by frontogenesis although local and temporary subduction can be much larger the subducted anticyclonic vortices are often coupled to upper ocean cyclonic vortices thus forming a baroclinic dipole that propagates at approximately 3 5 cm s and is capable of transporting the anomalous water properties far from the region of formation similarities with observations in the north atlantic subtropical convergence zone and near the gulf stream are discussed

a barotropic inverse tidal model for the arctic ocean 1 we describe high resolution 5 km grid linear dynamics and inverse models of arctic ocean barotropic tides obtained with the osu tidal inversion software otis package the 8 constituent dynamics based model uses the latest ibcao bathymetry and open boundary forcing from the recent tpxo 6 2 global barotropic tidal solution this model performs significantly better than the present benchmark arctic tidal model 14 km grid by z kowalik and a proshutinsky as judged by comparisons with 300 coastal tide gauges the greatest improvements are found in the canadian arctic archipelago nares strait and the baffin bay and labrador sea and can be explained by the higher resolution of the new model in these topographically complex regions the new arctic inverse model assimilates coastal and benthic tide gauges and topex poseidon and ers altimetry for further improvements of the 4 dominant constituents m2 s2 k1 and o1

flow of winter transformed pacific water into the western arctic abstract the dynamics of the flow of dense water through barrow canyon is investigated using data from a hydrographic survey in summer 2002 the focus is on the winter transformed bering water the highest volumetric mode of winter water in the chukchi sea which drains northward through the canyon in spring and summer the transport of this water mass during the time of the survey was 0 2 0 3 sv as the layer flowed from the head of the canyon to the mouth it sank decelerated and stretched strong cyclonic relative vorticity was generated on the seaward side of the jet which compensated for the stretching this adjustment was incomplete however in that it did not extend across the entire current possibly because of internal mixing due to shear instabilities the resulting vorticity structure of the flow at the canyon mouth was conducive for baroclinic instability and eddy formation multiple eddies of winter transformed bering water were observed along the chukchi beaufort shelfbreak those to the west of barrow canyon were in the process of being spawned by the eastward flowing shelfbreak current emanating from herald canyon while the single eddy observed to the east originated from the barrow canyon outflow it is argued that such an eddy formation is a major source of the ubiquitous cold core anti cyclones observed historically throughout the canada basin implications for the ventilation of the upper halocline of the western arctic are discussed

seasonal variation of upwelling in the alaskan beaufort sea impact of sea ice cover 1 data from a mooring array deployed from august 2002 to september 2004 are used to characterize differences in upwelling near the shelf break in the alaskan beaufort sea due to varying sea ice conditions the record is divided into three ice seasons open water partial ice and full ice the basic response is the same in each of the seasons roughly 8 h after the onset of easterly winds the shelf break jet reverses followed approximately 10 h later by upwelling of saltier water which is cold near the shelf break pacific winter water and warm at depth atlantic water the secondary circulation at the outer shelf is to first order consistent with a two dimensional ekman balance of offshore flow in the upper layer and onshore flow at depth there are however important seasonal differences in the upwelling overall the response is strongest in the partial ice season and weakest in the full ice season it is believed that these differences are dictated by the degree to which wind stress is transmitted through the pack ice as the strength of the wind forcing was comparable over the three seasons an eof based upwelling index is constructed using information about the primary flow secondary flow and hydrography the ability to predict upwelling using the wind record alone is explored which demonstrates that 90 of easterly wind events exceeding 9 5 m s 1 drive significant upwelling during certain periods the ice cover on the shelf became landfast which altered the upwelling and circulation patterns near the shelf break

interstitial water and sediment chemistries of lake aiguebelette savoy france abstract interstitial waters were collected from lake aiguebelette sediment savoy france using an in situ sampler major ions nutrients and trace metals fe and mn were measured early diagenesis in these sediments leads to the release of all the investigated elements po 4 nh 4 and h 4 sio 4 demonstrate significant concentration gradients reflecting organic matter decomposition thermodynamic calculations suggest that calcite which precipitates from the overlying waters dissolves in the pore fluids a simplified model is presented to account for the increase of ca 2 alk and h concentrations with depth mineralogical investigations using sem tem microprobe analysis and step dissolution of the sediment complete and corroborate the conclusions based on the study of interstitial waters i e calcium carbonate and silica dissolution

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

mesoscale eddies of the arctic ocean subsurface baroclinic eddies in the arctic ocean have a diameter of 10 20 km and are confined in depth between 50 and 300m during the arctic ice dynamics joint experiment aidjex in the central beaufort sea between march 1975 and may 1976 extensive information on eddy characteristics statistics and behavior was collected from four manned drifting ice camps during this 14 month period 146 eddies were encountered of which 19 were found to be repeated crossings making a total of 127 separate eddies observed during this period on the basis of the 1975 1976 aidjex data set it is concluded that eddies are 1 prevalent in the amerasia basin of the arctic ocean and in particular the beaufort sea where they may occupy up to a quarter of the available surface area 2 located in the depth range of 50 300 m although a few deeper eddies are also present 3 the second largest producers 32 of kinetic energy found within the upper 200 m of the beaufort sea and 4 predominantly anticyclonic in rotational tendency these eddies apparently originate north of point barrow alaska as a result of instability in the eastward flowing alaskan coastal current and transfer seasonally varying water properties from the chukchi sea and alaskan shelf into the arctic ocean they appear to translate in response to barotropic forcing over short time scales and over longer time periods move with the mean geostrophic field the season of formation for an eddy may be identified by the anomalous thermal properties still residing in its core

the arctic circumpolar boundary current we present high resolution simulations and observational data as evidence of a fast current flowing along the shelf break of the siberian and alaskan shelves in the arctic ocean thus far the arctic circumpolar boundary current acbc has been seen as comprising two branches the fram strait and barents sea branches fsb and bsb respectively here we describe a new third branch the arctic shelf break branch asbb we show that the forcing mechanism for the asbb is a combination of buoyancy loss and non local wind creating high pressure upstream in the barents sea the potential vorticity influx through the st anna trough dictates the cyclonic direction of flow of the asbb which is the most energetic large scale circulation structure in the arctic ocean it plays a substantial role in transporting arctic halocline waters and exhibits a robust seasonal cycle with a summer minimum and winter maximum the simulations show the continuity of the fsb all the way around the arctic shelves and the uninterrupted asbb between the st anna trough and the western fram strait the bsb flows continuously along the siberian shelf as far as the chukchi plateau where it partly diverges from the continental slope into the ocean interior the alaskan shelf break current asc is the analog of the asbb in the canadian arctic the asc is forced by the local winds and high upstream pressure in bering strait caused by the drop in sea surface height between the pacific and arctic oceans

new hydrographic measurements of the upper arctic western eurasian basin in 2017 reveal fresher mixed layer and shallower warm layer than 2005 2012 climatology in 2017 ice atmosphere ocean observing system autonomous drifting platforms provided extensive physical and biogeochemical data in the upper 350 m of the western eurasian basin through their 8 month drift across the amundsen basin the gakkel ridge the nansen basin and western fram strait comparison with woa13 climatology indicates a fresher surface layer and shallower warm layer in 2017 than in 2005 2012 the ice atmosphere ocean observing system 2017 data feature two halocline eddies in the amundsen basin and two atlantic water aw mesoscale structures in the nansen basin analysis of the global 1 12 mercator ocean operational system suggests that the halocline eddies resulted from instabilities in the frontal zone between fresher makarov waters and saltier eurasian waters this frontal region appears to have shifted further southeast in 2017 near 88 n 10 e compared to 2005 2012 the operational system depicts the large aw structure in the nansen basin 140 km crossed as far as 83 7 n 34 5 e as an aw meander from the arctic circumpolar boundary current which turned into an anticyclonic eddy about a month after the platforms drifted away the aw structure at 82 8 n 3 w northwest of the yermak plateau corresponds to an aw recirculating branch detaching from the yermak plateau slope back toward fram strait

surface cyclones in the era 40 dataset 1958 2001 part i novel identification method and global climatology abstract a novel method is introduced to generate climatological frequency distributions of meteorological features from gridded datasets the method is used here to derive a climatology of extratropical cyclones from sea level pressure slp fields a simple and classical conception of cyclones is adopted where a cyclone is identified as the finite area that surrounds a local slp minimum and is enclosed by the outermost closed slp contour this cyclone identification procedure can be applied to individual time instants and climatologies of cyclone frequency fc are obtained by simple time averaging therefore unlike most other climatologies the method is not based on the application of a tracking algorithm and considers the size of cyclones in combination with a conventional cyclone center tracking algorithm that allows the determination of cyclone life times and the location of cyclogenesis and cyclolysis additional frequency fields can be obtained for special categories of cyclones that are gener

upwelling on the continental slope of the alaskan beaufort sea storms ice and oceanographic response 1 the characteristics of pacific born storms that cause upwelling along the beaufort sea continental slope the oceanographic response and the modulation of the response due to sea ice are investigated in fall 2002 a mooring array located near 152w measured 11 significant upwelling events that brought warm and salty atlantic water to shallow depths when comparing the storms that caused these events to other aleutian lows that did not induce upwelling interesting trends emerged upwelling occurred most frequently when storms were located in a region near the eastern end of the aleutian island arc and alaskan peninsula not only were these storms deep but they generally had northward tending trajectories while the steering flow aloft aided this northward progression the occurrence of lee cyclogenesis due to the orography of alaska seems to play a role as well in expanding the meridional influence of the storms in late fall and early winter both the intensity and frequency of the upwelling diminished significantly at the array site it is argued that the reduction in amplitude was due to the onset of heavy pack ice while the decreased frequency was due to two different upper level atmospheric blocking patterns inhibiting the far field influence of the storms

characterizing the eddy field in the arctic ocean halocline ice tethered profilers itp deployed in the arctic ocean between 2004 and 2013 have provided detailed temperature and salinity measurements of an assortment of halocline eddies a total of 127 mesoscale eddies have been detected 95 of which were anticyclones the majority of which had anomalously cold cores these cold core anticyclonic eddies were observed in the beaufort gyre region canadian water eddies and the vicinity of the transpolar drift stream eurasian water eddies an arctic wide calculation of the first baroclinic rossby deformation radius rd has been made using itp data coupled with climatology rd 13 km in the canadian water and 8 km in the eurasian water the observed eddies are found to have scales comparable to rd halocline eddies are in cyclogeostrophic balance and can be described by a rankine vortex with maximum azimuthal speeds between 0 05 and 0 4 m s the relationship between radius and thickness for the eddies is consistent with adjustment to the ambient stratification eddies may be divided into four groups each characterized by distinct core depths and core temperature and salinity properties suggesting multiple source regions and enabling speculation of varying formation mechanisms

on the circulation of atlantic water in the arctic ocean an idealized eddy resolving numerical model and an analytic three layer model are used to develop ideas aboutwhatcontrolsthecirculationofatlanticwaterinthearctic ocean thenumericalmodelisforcedwith a surface heat flux uniform winds and a source of low salinity water near the surface around the perimeter of an arctic basin despite this idealized configuration the model is able to reproduce many general aspects of the arctic ocean circulation and hydrography including exchange through fram strait circulation of atlantic water a halocline ice cover and transport surface heat flux and a beaufort gyre the analytic model depends on a nondimensional number and provides theoretical estimates of the halocline depth stratification freshwater content and baroclinic shear in the boundary current an empirical relationship between freshwater content and sea surface height allows for a prediction of the transport of atlantic water in the cyclonic boundary current parameters typical of the arctic ocean produce a cyclonic boundary current of atlantic water of o 1 2 2sv where 1sv 10 6 m 3 s 21 and a halocline depth of o 200m in reasonable agreement with observations the theory compares well with a series of numerical model calculations in which mixing and environmental parameters are varied thus lending credibility to the dynamics of the analytic model in these models lateral eddy fluxes from the boundary and vertical diffusion in the interior are important drivers of the halocline and the circulation of atlantic water in the arctic ocean

wintertime warming of an arctic shelf in response to large scale atmospheric circulation 1 observations on the west spitsbergen shelf have shown that the dynamic response of the shelf to wind forcing has a profound effect on the heat content of the water hydrographic and atmospheric data have been analysed with respect to the relative importance of surface heat fluxes and advective processes on ocean temperature during the arctic winter of 2005 06 periods of sustained along shelf winds generated upwelling and cross shelf exchange causing extensive flooding of the coastal waters with warm atlantic water from the west spitsbergen current the winter temperature of the west spitsbergen shelf reverted to that typical of fall interrupting the normal cycle of sea ice formation in the region

eddy driven recirculation of atlantic water in fram strait eddy resolving regional ocean model results in conjunction with synthetic float trajectories and observations provide new insights into the recirculation of the atlantic water aw in fram strait that significantly impacts the redistribution of oceanic heat between the nordic seas and the arctic ocean the simulations confirm the existence of a cyclonic gyre around the molloy hole near 80 n suggesting that most of the aw within the west spitsbergen current recirculates there while colder aw recirculates in a westward mean flow south of 79 n that primarily relates to the eastern rim of the greenland sea gyre the fraction of waters recirculating in the northern branch roughly doubles during winter coinciding with a seasonal increase of eddy activity along the yermak plateau slope that also facilitates subduction of aw beneath the ice edge in this area

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

hydrography of the west spitsbergen current svalbard branch autumn 2001 1 the atlantic inflow is the primary source of water and heat to the arctic ocean a large portion enters through fram strait where it splits into the yermak and svalbard branches in october to november 2001 the uscgc healy occupied five oceanographic transects across the svalbard branch west and north of spitsbergen temperature and salinity sections show the warm salty atlantic water cooling and freshening as it flows along the continental slope for 553 km the temperature in the upper 500 m of the water column decreased by 0 25 c 100 km implying a heat flux across the sea surface of up to 520 w m2 if one assumes a nominal current of speed of 0 1 m s a temperature salinity t s analysis shows that the shape of the t s curves can be explained in terms of the ratio of the atmospheric to ice melt heat flux the observations imply that ice melt accounts for progressively more surface cooling as the flow moves toward the arctic ocean an autonomous underwater vehicle completed a vertical section in the region of maximum water mass gradient and revealed layer interleaving in fine detail data from this cruise extend a long time series of atlantic layer source temperature beginning in 1910 saloranta and haugan 2001 the extended observations show that after the temperature of the atlantic layer inflow reached a peak in 1992 it cooled to a minimum in 1998 and rose again through 2001

western arctic shelfbreak eddies formation and transport abstract the mean structure and time dependent behavior of the shelfbreak jet along the southern beaufort sea and its ability to transport properties into the basin interior via eddies are explored using high resolution mooring data and an idealized numerical model the analysis focuses on springtime when weakly stratified winter transformed pacific water is being advected out of the chukchi sea when winds are weak the observed jet is bottom trapped with a low potential vorticity core and has maximum mean velocities of o 25 cm s 1 and an eastward transport of 0 42 sv 1 sv 106 m3 s 1 despite the absence of winds the current is highly time dependent with relative vorticity and twisting vorticity often important components of the ertel potential vorticity an idealized primitive equation model forced by dense weakly stratified waters flowing off a shelf produces a mean middepth boundary current similar in structure to that observed at the mooring site the model boundary current is also highly v

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

significant role of the north icelandic jet in the formation of denmark strait overflow water the largest dense water plume feeding the lower limb of the atlantic meridional overturning circulation from the nordic seas comes from denmark strait overflow water measurements of hydrography and water velocity north of iceland and ocean model simulations indicate that a significant part of this water is supplied by the north icelandic jet

arctic warming through the fram strait oceanic heat transport from 3 years of measurements we present estimates of volume and heat transport through fram strait for the period 1997 to 2000 from data of moored instruments full depth volume transports at 78 55 n were in the order of 10 sv both northwards and southwards with an annual mean net transport between 2 and 4 sv to the south the temperature of the northward flow of atlantic water had a strong seasonality with a minimum in winter nevertheless the northward heat transport was highest in winter caused by the winter maximum of northward volume transport during the three years of observation the heat transport in the west spitsbergen current increased from 28 to 46 tw as a result of both increased speed and temperature in contrast to the west spitsbergen current the volume and heat transport of east greenland current remained fairly constant an integration over a subsection of the east greenland current showed similar values of volume transport to that obtained by measurements in the 1980s foldvik et al 1988 the southward heat transport through modified atlantic water weakened slightly between 1997 and 1999 despite increased temperatures

circulation and transformation of atlantic water in the eurasian basin and the contribution of the fram strait inflow branch to the arctic ocean heat budget abstract the inflows of atlantic water from the nordic seas to the arctic ocean through fram strait and over the barents sea are examined and their pathways and transformations in the eurasian basin are described based primarily on hydrographic observations from two cruises with rv polarstern in 2007 and 2011 the contrast between the high salinity atlantic water core in the nansen basin and the lower atlantic water salinity in the amundsen basin combined with a salinity minimum below the atlantic layer suggest that the fram strait branch mainly remains in the nansen basin while the barents sea branch continues along the continental slope enters the amundsen basin and provides most of the atlantic water in the makarov and canada basins to examine the consequences of such a circulation pattern recently published estimates of the in and outflows of volume and liquid freshwater through the barents sea bering strait and the canadian arctic archipelago as well as river runoff net precipitation and ice export are reviewed and added together to achieve volume and freshwater balances net outflows through fram strait of 2 3 sv and 100 msv respectively are required this is reasonably close to the recently reported fram strait transport estimates the net outflows are separated into two parts upper layer transports less dense than the entering atlantic water and lower layer transports as dense as or denser than the atlantic water the largest net volume outflow occurs in the lower layer 1 65 sv while the liquid freshwater is almost exclusively exported in the 0 64 sv net outflow in upper layer leading to unrealistically low salinities in the upper layer compared with observations atlantic water is north of svalbard transformed into less saline surface water through melting of sea ice which can supply the necessary higher salinity halocline water to the upper layer 1 23 sv of halocline water of salinity 34 2 must be added to obtain a more realistic salinity of 33 1 leading to a total export of 1 84 sv upper layer water in the east greenland current existing observations of the net transports into and out of the arctic ocean through fram strait in different temperature classes are used to estimate the heat loss of the atlantic water entering the arctic ocean through fram strait about 10 tw are supplied to the atmosphere in addition to the loss of 24 tw occurring in connection with the formation of the halocline water if the hypothesis that the fram strait branch remains in the nansen basin is true it implies a heat loss between 5 and 15 w m 2 in the nansen basin depending upon how much heat is temporarily stored in the water column this is high compared to the 2 w m 2 commonly cited as the ocean heat flux to the atmosphere in the arctic ocean

two configurations of the western arctic shelfbreak current in summer abstractdata from a closely spaced array of moorings situated across the beaufort sea shelfbreak at 152 w are used to study the western arctic shelfbreak current with emphasis on its configuration during the summer season two dynamically distinct states of the current are revealed in the absence of wind with each lasting approximately one month the first is a surface intensified shelfbreak jet transporting warm and buoyant alaskan coastal water in late summer this is the eastward continuation of the alaskan coastal current it is both baroclinically and barotropically unstable and hence capable of forming the surface intensified warm core eddies observed in the southern beaufort sea the second configuration present during early summer is a bottom intensified shelfbreak current advecting weakly stratified chukchi summer water it is baroclinically unstable and likely forms the middepth warm core eddies present in the interior basin the mesoscale instabilities extract energy from the mean flow such

the atlantic water boundary current in the nansen basin transport and mechanisms of lateral exchange data from a shipboard hydrographic survey near 30 e in the nansen basin of the arctic ocean are used to investigate the structure and transport of the atlantic water boundary current two high resolution synoptic crossings of the current indicate that it is roughly 30 km wide and weakly mid depth intensified using a previously determined definition of atlantic water the transport of this water mass is calculated to be 1 6 0 3 sv which is similar to the transport of atlantic water in the inner branch of the west spitsbergen current at the time of the survey a small anti cyclonic eddy of atlantic water was situated just offshore of the boundary current the data suggest that the feature was recently detached from the boundary current and due to compensating effects of temperature and salinity on the thermal wind shear the maximum swirl speed was situated below the hydrographic property core two other similar features were detected within our study domain suggesting that these eddies are common and represent an effective means of fluxing warm and salty water from the boundary current into the interior an atmospheric low pressure system transiting south of our study area resulted in southeasterly winds prior to and during the field measurements a comparison to hydrographic data from the pacific water boundary current in the canada basin under similar atmospheric forcing suggests that upwelling was taking place during the survey this provides a second mechanism related to cross stream exchange of heat and salt in this region of the nansen basin this article is protected by copyright all rights reserved

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

the yermak pass branch a major pathway for the atlantic water north of svalbard an upward looking acoustic doppler current profiler deployed from july 2007 to september 2008 in the yermak pass north of svalbard gathered velocity data from 570 m up to 90 m at a location covered by sea ice 10 months out of 12 barotropic diurnal and semi diurnal tides are the dominant signals in the velocity more than 70 of the velocity variance in winter baroclinic eddies at periods between 5 and 15 days and pulses of one to two month periodicity are observed in the atlantic water layer and are associated with a shoaling of the pycnocline mercator ocean global operational model with daily and 1 12 degree spatial resolution is shown to have skills in representing low frequency velocity variations 1 month in the west spitsbergen current and in the yermak pass model outputs suggest that the yermak pass branch has had a robust winter pattern over the last 10 years carrying on average 31 of the atlantic water volume transport of the west spitsbergen current 36 in autumn winter however those figures have to be considered with caution as the model neither simulates tides nor fully resolves eddies and ignores residual mean currents that could be significant

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

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

age characteristics of a shelf break eddy in the western arctic and implications for shelf basin exchange 1 radioisotope evaluation of a cold core anticyclonic eddy surveyed in september 2004 on the chukchi sea continental slope was used to determine its age since formation over the shelf environment because the eddy can be shown to have been generated near the shelf break initial conditions for several age dependent tracers could be relatively well constrained a combination of 228ra 226ra excess 224ra and 228th 228ra suggested an age on the order of months this age is consistent with the presence of elevated concentrations of nutrients organic carbon suspended particles and shelf derived neritic zooplankton within the eddy compared to ambient offshore water in the canada basin but comparable to values measured in the chukchi shelf and shelf break environment hence this feature at the edge of the deep basin was poised to deliver biogeochemically significant shelf material to the central arctic ocean