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

atmospheric patterns forcing two regimes of arctic circulation a return to anticyclonic conditions atmospheric sea level pressure slp patterns associated with two regimes of ice ocean circulation are identified by sorting the data into bins depending on whether modeled arctic ocean circulation was anticyclonic or cyclonic the transition between regimes is a zonally symmetric slp cell with maximum amplitude at the north pole from 1946 to 1997 four anticyclonic and four cyclonic regimes track the arctic ocean slp oscillation recent slp data suggest that the ocean atmosphere system will shift or has already shifted to an anticyclonic state

return of the cold halocline layer to the amundsen basin of the arctic ocean implications for the sea ice mass balance 1 ctd measurements from the arctic ocean 2001 expedition reveal that the cold halocline layer chl has returned to the amundsen basin at a position close to that found during the oden 91 expedition river water from the siberian shelves formed a strong freshwater front in the amundsen basin extending from the gakkel ridge to the lomonosov ridge furthermore we show from model computations that the presence of a chl may increase winter sea ice growth by 0 25 m over one season compared to a case with a non existing chl due to increased vertical heat flux from the warm atlantic water the difference in sea ice growth is due to a much shallower winter convection with a chl present which is not able to reach into the warm atlantic layer resulting in a considerably smaller oceanic heat flux

long term variability of arctic ocean waters evidence from a reanalysis of the ewg data set 1 we have examined interannual to decadal variability of water properties in the arctic ocean using an enhanced version of the 1948 1993 data released earlier under the gore chernomyrdin environmental bilateral agreement that earlier data set utilized gridded fields with decadal time resolution whereas we have developed a data set with annual resolution we find that beginning about 1976 most of the upper arctic ocean became significantly saltier possibly related to thinning of the arctic ice cover there are also indications that a more local upper ocean salinity increase in the eurasian basin about 1989 may not have originated on the shelf as had been suggested earlier in addition to the now well established warming of the atlantic layer during the early 1990s there was a similar cyclonically propagating warm event during the 1950s more remarkable however was a pervasive atlantic layer warming throughout most of the arctic ocean from 1964 1969 possibly related to reduced vertical heat loss associated with increased upper ocean stratification a cold period prevailed during most of the 1970s and 1980s with several very cold events appearing to originate near the kara and laptev shelves finally we find that the silicate maximum in the central arctic ocean halocline eroded abruptly in the mid 1980s demonstrating that the redistribution of pacific waters and the warming of the atlantic layer reported from other observations during the 1990s were distinct events separated in time by perhaps 5 years we have made the entire data set publicly available

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

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

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

pacific freshwater river water and sea ice meltwater across arctic ocean basins results from the 2005 beringia expedition 1 pacific water sea ice meltwater and river water are the primary sources of freshwater in the arctic ocean we have determined their relative fractions on a transect across the arctic ocean section 2005 expedition onboard ib oden which took place from 21 august to 23 september 2005 the transect began north of alaska continued through the central canada basin to the alpha ridge and into the makarov basin and ended in amundsen basin pacific freshwater and river water were the major sources of freshwater throughout the central canada basin and into makarov basin with river water fractions sometimes considerably higher than pacific water in the top 50 m pacific freshwater extended to depths of about 200 m pacific water found over the alpha ridge and in the amundsen basin is suggested to have been transported there in the transpolar drift the inventories of pacific freshwater and river water were roughly constant along the section through most of the canada and makarov basins river water fractions were greater than those of pacific freshwater in the amundsen basin sea ice meltwater fractions were negative reflecting net ice formation or near zero throughout most of the section a comparison of freshwater inventories with those at stations occupied during expeditions in 1991 1994 and 1996 indicated an increase in river water inventories in the makarov and amundsen basins on the eurasian side of the arctic ocean

arctic ocean variability derived from historical observations 1 this study has been motivated by reports of extraordinary change in the arctic ocean observed in recent decades most of these observations are based on synoptic measurements while evaluation of anomalies requires an understanding of the underlying long term variability historical climatologies give reference means and while these datasets are a reliable source of the mean atlantic layer temperature they significantly underestimate variability using historical data we calculated statistical parameters for selected arctic ocean regions they demonstrate a high level of atlantic layer temperature variability in the nansen basin and sea surface salinity fluctuations on the siberian shelf and the amundsen basin these estimates suggest strong limitations on our ability to define amplitudes of anomalies by comparing recent synoptic measurements with climatologies especially for regions characterized by strong variability

the laptev sea as a source for recent arctic ocean salinity changes this study was motivated by observations of significant salinification of the upper eurasian basin that began around 1989 observational data and modeling results provide evidence that increased arctic atmospheric cyclonicity in the 1990s resulted in a dramatic increase of the salinity in the eurasian basin two mechanisms account for the laptev sea salinization eastward diversion of russian rivers and increased brine formation due to enhanced ice production in numerous leads in the laptev sea ice cover both these mechanisms are linked to changes in wind patterns and were essential to the formation of salinity anomalies the resulting laptev sea salinity anomaly was advected to the central eurasian basin the strong salinization over the eurasian basin altered the formation of cold halocline waters weakened vertical stratification and released heat upward from below the cold halocline layer our analysis suggests that local processes in the laptev sea may have a basin wide impact on the thermohaline structure of the arctic ocean

the impact of freshening on phytoplankton production in the pacific arctic ocean since the 1990s drastic melting of sea ice and continental ice in the arctic region triggered by global warming has caused substantial freshening of the arctic ocean while several studies attempted to quantify the magnitude of this freshening its consequences on primary producers remain poorly documented in this study we evaluate the impact of the freshwater content fwc of the upper arctic ocean on phytoplankton across the pacific sector from the bering strait 65 n to the north pole 86 n during summer 2008 we performed statistical analyses on the physical biogeochemical and biological data acquired during the chinare 2008 cruise to investigate the effect of sea ice melting on the arctic phytoplankton we found that the strong freshening observed in the canada basin had a negative impact on primary producers as a result of the deepening of the nitracline and the establishment of a subsurface chlorophyll maximum scm in contrast regions with lower freshening such as the chukchi shelf and the marginal ice zone miz over the chukchi borderland exhibited a shallower nitracline sustaining relatively high primary production and biomass our results imply that the predicted increase freshening in future years will likely cause the arctic deep basin to become more oligotrophic because of weaker surface nutrient renewal from the subsurface ocean despite higher light penetration

salinity trends on the siberian shelves 1 we present an analysis of observed long term 100 year salinity trends on the freshwater dominated siberian continental shelves a multiple regression was performed in the white sea ws the kara sea ks the laptev sea ls and the east siberian sea ess since 1930 the ws has gained freshwater while the ess has lost it consistent with river discharge trends over this period over the past 20 years increases in both river discharge and direct precipitation can explain observed salinity decreases in the ws but not in the ks salinity trends in the ls and ess indicate that ocean circulation plays a dominate role in these areas where in recent years freshwater has been diverted eastward along the coast rather than northward toward the deep ocean

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

arctic warming evolution and spreading of the 1990s warm event in the nordic seas and the arctic ocean 1 observations in the arctic ocean revealed changes in oceanic temperature salinity and ice cover of the 1990s as compared with earlier data with a numerical model we favorably reproduce the development and subsequent propagation of temperature anomalies in water of atlantic origin in the 1980s and 1990s these propagated into the arctic ocean via the barents sea and the fram strait two warm anomalies entered the arctic ocean through these passages while the first smaller anomaly only warmed up the western eurasian basin the second large anomaly spread far into the eastern eurasian basin and across the lomonossov ridge into the western arctic basins intensified boundary currents during the high nao state in the first half of the 1990s significantly influenced the amplitude and speed of propagation of the temperature anomalies inside the arctic ocean in contrast to the notion of a continuous warming process during the 1990s our model results suggest the warming of the atlantic layer in the arctic ocean occurred in the form of events the event with the largest anomalous heat input during the modeled period entered the arctic between 1989 and 1994 it is possible to trace back the additional heat input into the arctic to an increased volume inflow via the faroer scotland passage and reduced heat loss to the atmosphere in the early 1990s after a weaker warm inflow in the second half of the 1990s the most recent observations and the model results point to a recurring warm anomaly in the inflow from 1999 onward

changes in the bering sea region atmosphere ice water system in the second half of the twentieth century abstract we examine the long range variability in the oceanographic regime of the bering sea during the second half of the twentieth century using the largest t s data set available containing about 58 000 stations we focus on changes in the ice regime and atmospheric processes over the bering sea and western arctic significant differences in the physical state of the bering sea were found between a group of anomalous cold 1955 1964 1971 1972 1975 1976 1977 1984 1988 years and warm 1958 1959 1962 1963 1967 1978 1981 1982 1987 years the time spatial eof analyses product of the first components show a general cooling in the bering sea in 1953 1977 and 1978 1993 and a strong warming in 1977 1978 likewise the spatial distribution of eof temperature 2 4 components indicates opposite thermal states in the western and eastern part of the bering sea if it becomes warmer in the eastern sector it becomes cooler in the western interaction between the aleutian low and siberian high determines the change over the bering sea region

thinning of the arctic sea ice cover comparison of sea ice draft data acquired on submarine cruises between 1993 and 1997 with similar data acquired between 1958 and 1976 indicates that the mean ice draft at the end of the melt season has decreased by about 1 3 m in most of the deep water portion of the arctic ocean from 3 1 m in 1958 1976 to 1 8 m in the 1990s the decrease is greater in the central and eastern arctic than in the beaufort and chukchi seas preliminary evidence is that the ice cover has continued to become thinner in some regions during the 1990s

recent freshening in the kara sea siberia recorded by stable isotopes in arctic bivalve shells oxygen and stable carbon isotope records along the growth direction on shells of the bivalve species astarte borealis and serripes groenlandicus reliably record all important aspects of the bottom water hydrography in the shallow southeastern kara sea despite uncertainties about the isotopic range due to sparse sampling and the possibility of growth rate changes changing freshwater supply from the rivers ob and yenisei is the main cause for seasonal temperature and salinity variations near the three sampling locations in 20 to 70 m water depth as suggested by ctd measurements and modeling peak winter salinity of the simulated hydrographic data series and peak winter values in the isotope records follow negative trends which indicate a freshening of the bottom water due to an increasing fraction of river water during the 1990s this freshening affected the whole kara sea and coincided with a lowering of regional air pressure gradients as indicated by the declining arctic oscillation index the resulting weakening of the prevailing southwesterly winds diminished the inflow of saline atlantic derived water from the barents sea through the kara strait in the southwest and additionally reduced the export of river water toward the north and northeast into the arctic basin saline atlantic derived water thus was replaced by freshwater which was successively accumulated in the kara sea and accordingly imprinted on the stable isotope composition of the bivalve shells the 1990s freshening in the kara sea thus may be caused by natural variations rather than being a signal for global change

nonlinear interdecadal changes of the el nino southern oscillation nonlinear interdecadal changes in the el nino southern oscillation enso phenomenon are investigated using several tools a nonlinear canonical correlation analysis nlcca method based on neural networks a hybrid coupled model and the delayed oscillator theory the leading nlcca mode between the tropical pacific wind stress ws and sea surface temperature sst reveals notable interdecadal changes of enso behaviour before and after the mid 1970s climate regime shift with greater nonlinearity found during 1981 99 than during 1961 75 spatial asymmetry for both sst and ws anomalies between warm el nino and cool la nina events was significantly enhanced in the later period during 1981 99 the location of the equatorial easterly anomalies was unchanged from the earlier period but in the opposite enso phase the westerly anomalies were shifted eastward by up to 25 according to the delayed oscillator theory such an eastward shift would lengthen the duration of the warm events by up to 45 but leave the duration of the cool events unchanged supporting evidence was found from a hybrid coupled model built with the lamont dynamical ocean model coupled to a statistical atmospheric model consisting of either the leading nlcca or cca mode

landfast ice affects the stability of the arctic halocline evidence from a numerical model landfast ice covers large surface areas of the winter siberian seas the immobile landfast ice cover inhibits divergent and convergent motion hence dynamical sea ice growth and redistribution decouples winter river plumes in coastal seas from the atmosphere and positions polynyas at the landfast ice edge offshore in spite of the potentially large effects state of the art numerical models usually do not represent landfast ice in its correct extent a simple parametrization of landfast ice based on bathymetry and internal sea ice strength is introduced and its effects on the simulated arctic ocean are demonstrated the simulations suggest that the siberian landfast ice impacts the arctic halocline stability through enhanced brine production in polynyas located closer to the shelf break and by redirecting river water to the canadian basin these processes strengthen the halocline in the canadian basin but erode its stability in the makarov and eurasian basins

inter annual to decadal sea level variability in the coastal zones of the norwegian and siberian seas the role of atmospheric forcing inter annual to decadal sea level variations from tide gauge records in the coastal zones of the norwegian and siberian seas are examined for the period 1950 2010 using a combination of hydrographic observations wind data and theory we identify two large areas of highly coherent sea level variability one that includes the norwegian barents and kara seas and another one that includes the laptev east siberian and chukchi seas we provide evidence of a new contribution to the sea level variability along the norwegian coast associated with the poleward propagation of sea level fluctuations along the eastern boundary of the north atlantic when this propagating signal is combined with the local wind we are able to explain over 70 of the variance along the norwegian coast the steric component explains 61 of the sea level corrected for the inverse barometer variability along the norwegian coast the high coherency between the sea level along the norwegian coast and that in the barents and kara seas suggests that part of the norwegian signal propagates further north into these regions we introduce an atmospheric vorticity index that explains much of the sea level variability in the laptev east siberian and chukchi seas with correlations ranging from 0 73 to 0 81 in the east siberian sea we identify a sea level increase of 22 cm between 2000 and 2003 which is partly explained by the vorticity index and a decline of 15 cm after 2003 which we relate to the strengthening of the beaufort gyre

wind driven summer surface hydrography of the eastern siberian shelf 1 high interannual variability of summer surface salinity over the laptev and east siberian sea shelves derived from historical records of the 1950s 2000s is attributed to atmospheric vorticity variations in the cyclonic regime positive vorticity the eastward diversion of the laptev sea riverine water results in a negative salinity anomaly to the east of the lena delta and farther to the east siberian sea and a positive anomaly to the north of the lena delta anticyclonic negative vorticity results in negative salinity anomalies northward from the lena delta due to freshwater advection toward the north and a corresponding salinity increase eastward

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