origin of freshwater and polynya water in the arctic ocean halocline in summer 2007 extremely low summer sea ice coverage in the arctic ocean in 2007 allowed extensive sampling and a wide quasi synoptic hydrographic and 18o dataset could be collected in the eurasian basin and the makarov basin up to the alpha ridge and the east siberian continental margin with the aim of determining the origin of freshwater in the halocline fractions of river water and sea ice meltwater in the upper 150 m were quantified by a combination of salinity and 18o in the eurasian basin two methods applying the preformed phosphate concentration po and the nitrate to phosphate ratio n p were compared to further differentiate the marine fraction into atlantic and pacific derived contributions while po based assessments systematically underestimate the contribution of pacific derived waters n p based calculations overestimate pacific derived waters within the transpolar drift due to denitrification in bottom sediments at the laptev sea continental margin within the eurasian basin a west to east oriented front between net melting and production of sea ice is observed outside the atlantic regime dominated by net sea ice melting a pronounced layer influenced by brines released during sea ice formation is present at about 30 to 50 m water depth with a maximum over the lomonosov ridge the geographically distinct definition of this maximum demonstrates the rapid release and transport of signals from the shelf regions in discrete pulses within the transpolar drift the ratio of sea ice derived brine influence and river water is roughly constant within each layer of the arctic ocean halocline the correlation between brine influence and river water reveals two clusters that can be assigned to the two main mechanisms of sea ice formation within the arctic ocean over the open ocean or in polynyas at the continental slope where relatively small amounts of river water are found sea ice formation results in a linear correlation between brine influence and river water at salinities of about 32 to 34 in coastal polynyas in the shallow regions of the laptev sea and southern kara sea sea ice formation transports river water into the shelf s bottom layer due to the close proximity to the river mouths this process therefore results in waters that form a second linear correlation between brine influence and river water at salinities of about 30 to 32 our study indicates which layers of the arctic ocean halocline are primarily influenced by sea ice formation in coastal polynyas and which layers are primarily influenced by sea ice formation over the open ocean accordingly we use the ratio of sea ice derived brine influence and river water to link the maximum in brine influence within the transpolar drift with a pulse of shelf waters from the laptev sea that was likely released in summer 2005

properties of the atlantic derived halocline waters over the laptev sea continental margin evidence from 2002 to 2009 1 a series of transects carried out in 2002 2009 across the laptev sea continental margin show consistent cross slope differences of the lower halocline water lhw over the slope the lhw core is on average warmer and saltier by 0 39 c and 0 26 practical salinity unit respectively relative to the off slope lhw underlying atlantic water aw thermohaline properties exhibit an opposite pattern it is colder and fresher over the slope and warmer and saltier off the slope although on slope and off slope lhws have different formation histories our results suggest that an important part of the heat and salt lost from the aw is gained by the overlying lhw over the continental slope area this implies the role of enhanced vertical mixing over the sloping topography which contributes to the difference between the on and off slope lhw properties the distribution of chemical tracers dissolved oxygen and nutrients provides further evidence supporting this interpretation and additionally suggests that the lhw may also be influenced by water from the outer shelf

on the origin of the chemical properties of the arctic ocean halocline profiles of chemical constituents in seawater above the alpha ridge in the central arctic ocean obtained during the canadian expedition to study the alpha ridge cesar support a model in which the halocline is maintained by dense saline water produced on the continental shelves within the arctic ocean by the formation of sea ice it is argued that nutrient regeneration on the continental shelves largely accounts for the nutrient maximum that has been observed in the upper halocline over a wide region of the arctic ocean and that while the bering sea and north altantic can be recognized as origins of halocline water water masses from these regions undergo sufficient changes in their chemical properties within the arctic ocean significant that they no longer retain their identity in the halocline

hydrographic conditions during the 2002 sbi process experiments abstract a review of the hydrographic data from the 2002 western arctic shelf basin interactions sbi process cruises permits the following conclusions 1 temperature salinity relationships were similar to canonical descriptions but at five stations in the outer shelf slope region warm high salinity atlantic layer water appeared to have risen displaced the lower halocline and mixed with shelf upper halocline water 2 primary production in the sbi study region was strongly influenced by the advection of dissolved inorganic nitrogen din entering via bering strait this import of din ammonium nitrate nitrite is modified by local processes but without the bering strait inflow biological productivity in the sbi region would be much lower 3 in comparison to the inflowing atlantic waters din urea phosphate and din urea silicate ratios in the pacific waters that dominated the upper 150 m of the water column were low they were also low relative to redfield uptake ratios for phytoplankton 4 microbial processes continue to destroy din in significant quantities as the pacific waters transit the sbi region 5 nitrate and ammonium were the principal contributors to din nitrite concentrations were always

water masses and circulation in the eurasian basin results from the oden 91 expedition the oden 91 north pole expedition obtained oceanographic measurements on four sections in the nansen and amundsen basins of the eurasian basin and in the makarov basin of the canadian basin thereby proving the feasibility of carrying out a typical oceanographic program using an icebreaker in the arctic ocean the data show greater spatial variability in water structure and circulation than was apparent from previous data the results show that a clear front exists between the eurasian and canadian basins such that upper halocline water in the canadian basin is almost absent from the eurasian basin the lower halocline water produced in the barents kara sea region permeates much of the eurasian basin and flows along the continental slope into the canadian basin the deeper circulation is strongly influenced by topography three return flows of the atlantic layer are identified one over the nansen gakkel ridge one over the lomonosov ridge and a third flowing from the canadian basin the slight differences observed in salinity and temperature characteristics of the deeper waters of the nansen and amundsen basins do not lead to an obvious explanation of their origin or flow pattern

mafic and ultramafic enclaves in ustica island lavas inferences on composition of lower crust and deep magmatic processes abstract ustica island southern tyrrhenian sea is constituted of quaternary alkaline volcanics a variety of enclaves representative of deep to supra crustal settings were recently found in a hawaiitic lava flow enclaves consist of i ultramafic meta cumulates i e clinopyroxenites and wherlites characterized by variably deformed porphyroclastic to granoblastic textures ii mafic cumulates i e gabbros amphibole and troctolites the first often characterized by frequent amphibole breakdown coronas olivine ti augite plagioclase magnetite ilmenite rhonite in response to an h 2 o decrease during the ascent while the troctolites interpreted as meta cumulates iii microsyenites consist of anorthoclase and fe clinopyroxene organized in a granular sub ipidiomorphic texture amphibole is absent in ustica lavas and is found only in some old now exposed sub intrusive volcanic bodies this evidence suggests a late appearance of amphibole on the liquidus at a high crystal content that inhibits further ascent of the magma the importance of the amphibole as a medium pressure liquidus phase in ustica mafic magmas is in the bearings on the geochemistry of lavas e g in buffering na and ti abundances in trace elements partitioning etc density measurements pointed out higher values for clinopyroxenites 3160 to 3300 kg m 3 than for gabbros ca 2900 kg m 3 given the density contrast between enclaves and host lavas 2790 kg m 3 and assuming appropriate rheological models we calculated a minimum ascent rate of 0 01 m s corresponding to an ascent time in the range of 5 29 days for a depth of entrapment of 25 km

surface freshening in the arctic ocean s eurasian basin an apparent consequence of recent change in the wind driven circulation 1 data collected by an autonomous ice based observatory that drifted into the eurasian basin between april and november 2010 indicate that the upper ocean was appreciably fresher than in 2007 and 2008 sea ice and snowmelt over the course of the 2010 drift amounted to an input of less than 0 5 m of liquid freshwater to the ocean comparable to the freshening by melting estimated for those previous years while the observed change in upper ocean salinity over the melt period implies a freshwater gain of about 0 7 m results of a wind driven ocean model corroborate the observations of freshening and suggest that unusually fresh surface waters observed in parts of the eurasian basin in 2010 may have been due to the spreading of anomalously fresh water previously residing in the beaufort gyre this flux is likely associated with a 2009 shift in the large scale atmospheric circulation to a significant reduction in strength of the anticyclonic beaufort gyre and the transpolar drift stream

dense water formation in the laptev sea flaw lead 1 two primitive equation based models are used to estimate the formation of total volumes either of arctic cold halocline water chw intermediate water imw or deep water dw through freeze related salt rejection in the siberian laptev sea flaw lead system model a assumes that the rejected salt remixes with surface mixed water smw beyond the leads until salinities allow for contribution to the midlayers of either the chw the imw or the dw model b simulates direct salt rejection to the upper layer of the cold halocline and after remixing here further contribution to the midlayers of chw imw or dw averaging both model estimates laptev leads contribute either 0 161 sv of chw 0 075 sv of imw or 0 065 sv of dw which represents as much as 23 16 or 30 of arctic wide lead derived dense water contribution to the appropriate layer respectively northwestern laptev leads produce the greatest amount of dense water these lead sections show very short buoyancy equilibrium timescales 6 to 13 days and local dense water production may potentially be amplified by lateral brine injection into the cold halocline through bottom eddies central southern and southeastern leads generally produce little salt due to low surface water salinities as definite separation mechanisms and proportion distributions of rejected lead brines into chw iwm and dw are still unidentified in nature a combination of lead salt rejection and remixing model a and direct downward expulsion of brine packages model b is assumed to steer laptev lead dense water production

the contribution of alaskan siberian and canadian coastal polynyas to the cold halocline layer of the arctic ocean numerous arctic ocean circulation and geochemical studies suggest that ice growth in polynyas over the alaskan siberian and canadian continental shelves is a source of cold saline water which contributes to the maintenance of the arctic ocean halocline the purpose of this study is to estimate for the 1978 1987 winters the contributions of arctic coastal polynyas to the cold halocline layer of the arctic ocean the study uses a combination of satellite oceanographic and weather data to calculate the brine fluxes from the polynyas then an oceanic box model is used to calculate their contributions to the cold halocline layer of the arctic ocean this study complements and corrects a previous study of dense water production by coastal polynyas in the barents kara and laptev seas recurrent polynyas form on the canadian and alaskan coasts from banks island to the bering strait and on the siberian coast from the bering strait to the new siberian islands in the bering sea polynyas form in norton sound south and west of st lawrence island and in the gulf of anadyr two regions that account for almost 50 of the total dense water production are the siberian coastal polynyas in the adjacent regions of the gulf of anadyr and anadyr strait and the alaskan coastal polynyas which occur along the coast from cape lisburne to point barrow for all of the western arctic coastal regions examined the mean annual total brine flux is 0 5 0 2 sv combination of this flux with the contribution from the barents kara and laptev seas which is recalculated from data in the earlier study shows that over the entire arctic coastal polynyas generate about 0 7 1 2 sv of dense water this compares well with the theoretical estimates of 1 1 5 sv because an unknown fraction of the barents kara and laptev brine flux must go to the eurasian basin deep water the coastal polynyas alone cannot renew the halocline layer other potential brine generation mechanisms include overall freezing on the shelves and the response of the ice to infrequent violent storms for example during february 1982 an intense storm generated a large region of low ice concentration in the eastern chukchi sea over barrow canyon the refreezing of the region was followed by the flow of a dense plume down barrow canyon although the ocean dynamical response to this refreezing needs to be established the possible response of a barrow canyon flow to this refreezing event suggests that the overall refreezing in response to infrequent violent storms may be a potential source of the additional brine needed to maintain the arctic ocean halocline

geochemical profiles in the central arctic ocean their relation to freezing and shallow circulation temperature salinity nutrient tritium and oxygen isotope data collected during the lomonosov ridge experiment along a drift track between the makarov and fram basins over the lomonosov ridge are presented the relationship of these quantities to the processes that maintain the halocline in particular to the production of more saline waters by addition of brines formed during the freezing of seawater is described the results support the idea that the wide continental shelves of the arctic ocean play an important role in maintaining the halocline productivity and to the chemical and physical effects of freezing sea water a comparison of this ocean with its low productivity at least during winter with other oceanic regions should help to elucidate some of the effects of biological activity on marine chemistry for example trace metal cycling and speciation aagaard et al 1981 discussed the way in which the cold waters of the halocline which lie immediately below the surface mixed layer and extend to the top of the warm atlantic layer could be produced on the wide continental margins surrounding the arctic ocean the processes in volve freezing with release of highly saline brines having a temperature close to the freezing point of surface sea water this water flows over the shelves and into the central basin sinking then to the appropriate density surface the distribu tions of various chemical parameters will be affected in predictable ways by these processes as a part of the lomonosov ridge experiment lorex which ran from late march until the end of may 1979 a program was undertaken aimed at describing more accurate ly the hydrography of the central arctic ocean and studying the geochemistry of selected trace elements in this unusual environment to this end water samples were collected from a drifting ice station lorex satellite camp 1 for the measurement of salinity silicate phosphate 5 80 trace metals moore 1981 1983 carbon 14 tritium helium 3 caesium 137 caesium 134 strontium 90 plutonium ameri cium h d livingston et al manuscript in preparation 1983 alkalinity and ph ice cores were collected to investi gate the possibility of deducing the extent of temporal changes in the tritium content of the surface waters

disequilibria between226ra 210pb and 210po in the arctic ocean and the implications for chemical modification of the pacific water inflow abstract measurements have been made of226ra and both dissolved and particulate forms of210pb and210po in a vertical profile at 85 50 n 108 50 w in the arctic ocean in the upper water column226ra shows a concentration maximum that is coincident with one in the nutrients silicate phosphate and nitrate while at the same depth dissolved and particulate210pb and210po all show minimum concentrations it is suggested that the concentration maxima are partly due to sources of the respective elements in the continental shelf sediments the shelf waters being subsequently advected into the arctic ocean basins the210pb and210po minima have similarly been explained by interaction between the shelf sediments and overlying waters an estimate is made of the possible contributions of shelf sediments to the layer of silica rich water which covers the canada basin at a depth of 100 150 m residence times have been calculated for dissolved210pb and210po at various depths in the water column surface water residence times of dissolved and particulate forms of these radionuclides are longer than in surface atlantic waters probably due to lower biological activity in the surface waters of the canada basin an estimatee has been made of the average sinking velocity of particulate material

a compilation of igneous rock volumes at volcanic passive continental margins from interpreted seismic profiles abstract the rifting and breakup of continents and subsequent seafloor spreading give rise to passive continental margins many of which are underlain by enormous volumes of igneous rocks and termed volcanic passive margins the relationships between the igneous rocks rifting and mantle plumes remain unresolved despite extensive studies and proposed alternative models to support such studies we use published previously interpreted seismic reflection and refraction data to compile a dataset of igneous rock volumes and geometries at volcanic passive continental margins the volmir volcanic passive margin igneous rocks dataset is based on margin crossing profiles on which the volumes and geometries of both shallow seaward dipping reflector sdr and deeper high velocity lower crustal hvlc units can be measured it includes information about the ages of continental breakup and profile distances from the associated euler pole and from hotspots that may have played roles in the breakup process despite local variations the dataset shows general patterns the average ratio of sdr to hvlc volumes 0 3 0 4 is relatively consistent between profiles implying that formation of these units is related during continental breakup the volumes of igneous rocks display a moderate positive correlation with distances from the euler pole but only a weak negative correlation with distances from the nearest hotspot at the time of margin formation suggesting that in continental breakup lithospheric processes passive rifting have greater effects than hotspots active rifting these results suggest that this dataset will be useful for exploring aspects of the rifting process relationships between volcanic rifted margins and potential explanations for their similarities and differences

stable oxygen and carbon isotopes in planktonic foraminifera neogloboquadrina pachyderma in the arctic ocean an overview of published and new surface sediment data abstract a summary study on oxygen and carbon stable isotopes in planktonic foraminifera from arctic ocean floor appeared in marine geology 20 years ago spielhagen and erlenkeuser 1994 we revisit this topic with a wealth of new data focused on the western amerasian arctic a spotlight in the current climatic and oceanic change neogloboquadrina pachyderma the most abundant polar planktonic foraminiferal species is an important tool for reconstructing surface subsurface water changes in the arctic our new data on n pachyderma 150 250 m from the surface sediments show 18 o and 13 c values of 18 o and 13 c are both influenced by complex water sources water column structure and foraminiferal depth habitat the observed distribution of n pachyderma stable isotopes confirms a shallow habitat of this species in the sea ice covered central arctic especially in the canada basin probably in relation to the shallow chlorophyll maximum the associated light n pachyderma 18 o reflects the long term storage of fresh water at the shelf break a deeper dwelling of n pachyderma with heavier 18 o is supported by a more extensive photic zone and nutrient availability air sea exchange plays an important role in 13 c distribution and is consistent with heavy n pachyderma 13 c in the perennially ice covered central arctic ocean light 13 c composition at the shelf break is additionally influenced by shelf bottom waters enriched in isotopically light remineralized terrestrial carbon distribution of foraminiferal 13 c on the chukchi shelf reflects primary production patterns in the area

river runoff sea ice meltwater and pacific water distribution and mean residence times in the arctic ocean hydrographic and tracer data collected during ark iv 3 fs polarstern in 1987 arctic91 ib oden and aos94 ccgs louis s st laurent expeditions reveal the evolution of the near surface waters in the arctic ocean during the late 1980s and early 1990s salinity nutrients dissolved oxygen and 18 o data are used to quantify the components of arctic freshwater river runoff sea ice meltwater and pacific water the calculated river runoff fractions suggest that in 1994 a large portion of water from the pechora ob yenisey kotuy and lena rivers did not flow off the shelf closest to their river deltas but remained on the shelf and traveled via cyclonic circulation into the laptev and east siberian seas river runoff flowed off the shelf at the lomonosov ridge and most left the shelf at the mendeleyev ridge arctic91 and aos94 pacific water fraction estimates of upper halocline water the traditionally defined core of the pacific water mass document a decrease in extent compared to historical data the front between atlantic water and pacific water shifted from the lomonosov ridge location in 1991 to the mendeleyev ridge in 1994 the relative age structure of the upper waters is described by using the 3 h 3 he age the mean 3 h 3 he age measured in the halocline within the salinity surface of 33 1 0 3 is 4 3 1 7 years and that for the 34 2 0 2 salinity surface is 9 6 4 6 years lateral variations in the relative age structure within the halocline and atlantic water support the well known cyclonic boundary current circulation

sources and distribution of fresh water in the east greenland current abstract fresh water flowing from the arctic ocean via the east greenland current influences deep water formation in the nordic seas as well as the salinity of the surface and deep waters flowing from there this fresh water has three sources pacific water relatively fresh cf atlantic water river runoff and sea ice meltwater to determine the relative amounts of the three sources of fresh water in may 2002 we collected water samples across the east greenland current in sections from 81 5 n to the irminger sea south of denmark strait we used nitrate phosphate relationships to distinguish pacific waters from atlantic waters salinity to obtain the sum of sea ice melt water and river runoff water and total alkalinity to distinguish the latter river runoff contributed the largest part of the total fresh water component in some regions with some inventories exceeding 12 m pacific fresh water pacific source water s 32 cf atlantic source water s 34 9 typically provided about 1 3 of the river runoff contribution sea ice meltwater was very nearly non existent in the surface waters of all sections likely at least in part as a result of the samples being collected before the onset of the melt season the fresh water from the arctic ocean was strongly confined to near the greenland coast we thus conjecture that the main source of fresh water from the arctic ocean most strongly impacting deep convection in the nordic seas would be sea ice as opposed to fresh water in the liquid phase i e river runoff pacific fresh water and sea ice meltwater

effects of ocean acidification warming and melting of sea ice on aragonite saturation of the canada basin surface water 1 in 2008 surface waters in the canada basin of the arctic ocean were found to be undersaturated with respect to aragonite this is associated with recent extensive melting of sea ice in this region as well as elevated sea surface temperature and atmospheric co2 concentrations we have estimated the relative contribution of each of these controlling factors to the calcium carbonate saturation state w from observations of dissolved inorganic carbon total alkalinity and oxygen isotope ratio results indicate that the increase in atmospheric co2 has lowered surface w by 0 3 in the canada basin since the preindustrial period recent melting of sea ice has further lowered mean w by 0 4 and of this half was due to dilution of surface water and half was due to the change in air sea disequilibrium state surface water warming has generally counteracted the mean decrease in w by 0 1 citation yamamoto kawai m f a mclaughlin and e c carmack 2011 effects of ocean acidification warming and melting of sea ice on aragonite saturation of the canada basin surface water geophys res lett 38 l03601 doi 10 1029 2010gl045501

processes of multibathyal aragonite undersaturation in the arctic ocean during three years of study 2010 2012 the western arctic ocean was found to have unique aragonite saturation profiles with up to three distinct aragonite undersaturation zones this complexity is produced as inflow of atlantic and pacific derived water masses mix with arctic derived waters which are further modified by physiochemical and biological processes the shallowest aragonite undersaturation zone from the surface to 30 m depth is characterized by relatively low alkalinity and other dissolved ions besides local influence of biological processes on aragonite undersaturation of shallow coastal waters the nature of this zone is consistent with dilution by sea ice melt and invasion of anthropogenic co2 from the atmosphere a second undersaturated zone at 90 220 m depth salinity 31 8 35 4 occurs within the arctic halocline and is characterized by elevated pco2 and nutrients the nature of this horizon is consistent with remineralization of organic matter on shallow continental shelves bordering the canada basin and the input of the nutrients and co2 entrained by currents from the pacific inlet finally the deepest aragonite undersaturation zone is at greater than 2000 m depth and is controlled by similar processes as deep aragonite saturation horizons in the atlantic and pacific oceans the comparatively shallow depth of this deepest aragonite saturation horizon in the arctic is maintained by relatively low temperatures and stable chemical composition understanding the mechanisms controlling the distribution of these aragonite undersaturation zones and the timescales over which they operate will be crucial to refine predictive models this article is protected by copyright all rights reserved

source and formation of the upper halocline of the arctic ocean 1 the upper halocline of the arctic ocean has a distinct chemical signature with high nutrient concentrations as well as low oxygen and ph values this signature is formed in the chukchi and east siberian seas by a combination of mineralization of organic matter and release of decay products to the sea ice brine enriched bottom water salinity and total alkalinity data show that the fraction of sea ice brine in the nutrient enriched upper halocline water in the central arctic ocean is up to 4 in the east siberian sea the bottom waters with exceptional high nutrient concentration and low ph have typically between 5 and 10 of sea ice brine as computed from salinity and oxygen 18 values on the continental slope over bottom depths of 150 200 m the brine contribution was 6 at the nutrient maximum depth 50 100 m at the same location as well as over the deeper basin the silicate maximum was found over a wider salinity range than traditionally found in the canada basin in agreement with earlier observations east of the chukchi plateau a detailed evaluation of the chemical and the temperature salinity properties suggests at least two different areas for the formation of the nutrient rich halocline within the east siberian sea this has not been observed before 2004 and it could be a sign of a changing marine climate in the east siberian sea caused by more open water in the summer season followed by more sea ice formation and brine production in the fall winter

on the nature and origin of water masses in herald canyon chukchi sea synoptic surveys in summer 2004 2008 and 2009 abstract hydrographic and velocity data from three high resolution shipboard surveys of herald canyon in the northwest chukchi sea in 2004 2008 and 2009 are used to investigate the water masses in the canyon and their possible source regions both summer and winter pacific waters were observed in varying amounts in the different years although in general the summer waters resided on the eastern side of the canyon while the winter waters were located on the western flank the predominant summer water was bering summer water although some alaskan coastal water resided in the canyon in the two later years likely due to wind forcing both newly ventilated and remnant winter waters were found in the canyon but the amount lessened in each successive survey using mooring data from bering strait it is shown that a large amount of bering summer water in the western channel of the strait follows a relatively direct route into herald canyon during the summer months with an estimated advective speed of 10 20 cm s however while the winter water observed in 2004 was consistent with a bering strait source with a slower advective speed of 5 8 cm s the dense water in the canyon during 2008 and 2009 was more in line with a northern source this is consistent with sections to the west of the canyon and with previously reported measurements implying winter water formation on the east siberian shelf large scale wind patterns and polynya activity on the shelf are also investigated it was found that the former appears to impact more strongly the presence of dense water in herald canyon

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

arctic salinity anomalies and their link to the north atlantic during a positive phase of the arctic oscillation abstract many of the changes observed during the last two decades in the arctic ocean and adjacent seas have been linked to the concomitant abrupt decrease of the sea level pressure in the central arctic at the end of the 1980s the decrease was associated with a shift of the arctic oscillation ao to a positive phase which persisted throughout the mid 1990s the arctic salinity distribution is expected to respond to these dramatic changes via modifications in the ocean circulation and in the fresh water storage and transport by sea ice the present study investigates these different contributions in the context of idealized ice ocean experiments forced by atmospheric surface wind stress or temperature anomalies representative of a positive ao index wind stress anomalies representative of a positive ao index generate a decrease of the fresh water content of the upper arctic ocean which is mainly concentrated in the eastern arctic with almost no compensation from the western arctic sea ice contributes to about two third of this salinification another third being provided by an increased supply of salt by the atlantic inflow and increased fresh water export through the canadian archipelago and fram strait the signature of a saltier atlantic current in the norwegian sea is not found further north in both the barents sea and the fram strait branches of the atlantic inflow where instead a widespread freshening is observed the latter is the result of import of fresh anomalies from the subpolar north atlantic through the iceland scotland passage and enhanced advection of low salinity waters via the east icelandic current the volume of ice exported through fram strait increases by 20 primarily due to thicker ice advected into the strait from the northern greenland sector the increase of ice drift velocities having comparatively less influence the export anomaly is comparable to those observed during events of great salinity anomalies and induces substantial freshening in the greenland sea which in turn contributes to increasing the fresh water export to the north atlantic via denmark strait with a fresh water export anomaly of 7 msv the latter is the main fresh water supplier to the subpolar north atlantic the canadian archipelago contributing to 4 4 msv the removal of fresh water by sea ice under a positive winter ao index mainly occurs through enhanced thin ice growth in the eastern arctic winter sat anomalies have little impact on the thermodynamic sea ice response which is rather dictated by wind driven ice deformation changes the global sea ice mass balance of the western arctic indicates almost no net sea ice melt due to competing seasonal thermodynamic processes the surface freshening and likely enhanced sea ice melt observed in the western arctic during the 1990s should therefore be attributed to extra winter atmospheric effects such as the noticeable recent spring summer warming in the canada alaska sector or to other modes of atmospheric circulations than the ao especially in relation to the north pacific variability

beaufort gyre freshwater reservoir state and variability from observations 1 we investigate basin scale mechanisms regulating anomalies in freshwater content fwc in the beaufort gyre bg of the arctic ocean using historical observations and data collected in 2003 2007 specifically the mean annual cycle and interannual and decadal fwc variability are explored the major cause of the large fwc in the bg is the process of ekman pumping ep due to the arctic high anticyclonic circulation centered in the bg the mean seasonal cycle of liquid fwc is a result of interplay between the mechanical ep and thermal ice transformations factors and has two peaks one peak occurs around june july when the sea ice thickness reaches its minimum maximum ice melt the second maximum is observed in november january when wind curl is strongest maximum ep and the salt input from the growing ice has not yet reached its maximum interannual changes in fwc during 2003 2007 are characterized by a strong positive trend in the region varying by location with a maximum of approximately 170 cm a 1 in the center of ep influenced region decadal fwc variability in the period 1950 2000 is dominated by a significant change in the 1990s forced by an atmospheric circulation regime change the center of maximum fwc shifted to the southeast and appeared to contract in area relative to the pre 1990s climatology in spite of the areal reduction the spatially integrated fwc increased by over 1000 km 3 relative to climatology

transit time of river water in the bering and chukchi seas estimated from δ 18 o and radium isotopes abstract seawater samples for the measurements of 226ra 228ra and stable oxygen isotope 18o were collected from the bering and chukchi seas in the summer of 2014 the fractions of meteoric water fmw and sea ice melted water fsim were estimated based on the mass balance of salinity and 18o with a three end member mixing model our results showed that the average fmw increased northward from the bering basin to the canada basin while the fsim distributed homogeneously the lowest fmw and 228ra 226ra a r values were found in the upper bering basin with little terrestrial input the highest fmw but low 228ra 226ra a r appeared in the northern chukchi sea and the canada basin ascribing to the current driven accumulation of freshwater and its long residence time more abundant sea ice melted water was found on the pack ice edge indicating the trap of earlier melted waters by the ice pack based upon the linear relationships between 228ra 226ra a r and fmw in the bering shelf and the chukchi shelf the transit time for the pacific inflow was constrained the transit time of river water from the bering shelf to the chukchi shelf was estimated as 0 2 4 4 years with an average of 1 6 1 5 years while that from the chukchi shelf to the canada basin was 10 2 13 2 years with an average of 11 8 1 1 years the spatial variation of the transit time was mainly affected by the current intensity our study highlights the importance of in depth evaluation for the subarctic arctic exchange