propagation of the great salinity anomaly of the 1990s around the northern north atlantic 1 time series of t and s extending through 2001 are used to describe propagation of the great salinity anomaly of the 1990s gsa 90s comparison of the distance time relations for the gsa 70s 80s and 90s reveals a substantial intensification of the large scale circulation in the northern north atlantic especially in the subarctic gyre between newfoundland and the faroes the advection rate of the gsa 70s 80s and 90s between newfoundland and the faroe shetland channel is conservatively estimated to have been 3 5 10 and 10 cm s respectively the circulation intensification apparently occurred within a decade between the gsa 70s and 80s during the next decade the advection rate increased from 10 to 13 cm s between newfoundland and iceland basin the gsa 90s was advected towards the faroe shetland channel by the northern iceland basin s branch of the north atlantic current whereas the contribution of the southern branch via the rockall trough was minimal

freshwater content variability in the arctic ocean 1 arctic ocean model simulations have revealed that the arctic ocean has a basin wide oscillation with cyclonic and anticyclonic circulation anomalies arctic ocean oscillation aoo that has a prominent decadal variability proshutinsky and johnson 1997 this study explores how the simulated aoo affects the arctic ocean stratification and its relationship to the sea ice cover variations the simulation uses the princeton ocean model coupled to sea ice hakkinen and mellor 1992 hakkinen 1999 the surface forcing is based on national centers for environmental prediction national center for atmospheric research reanalysis and its climatology of which the latter is used to force the model spin up phase our focus is to investigate the competition between ocean dynamics and ice formation melt on the arctic basin wide freshwater balance we find that changes in the atlantic water inflow can explain almost all of the simulated freshwater anomalies in the main arctic basin the atlantic water inflow anomalies are an essential part of aoo which is the wind driven barotropic response to the arctic oscillation ao the baroclinic response to ao such as ekman pumping in the beaufort gyre and ice melt freeze anomalies in response to ao are less significant considering the whole arctic freshwater balance

a simulation of thermohaline effects of a great salinity anomaly abstract model simulations of an idealistic great salinity anomaly gsa demonstrate that variability in the sea ice export from the arctic when concentrated to short pulses can have a large influence on the meridional heat transport and can lead to an altered overturning state one single freshwater disturbance resulting from excess ice export as in 1968 can disrupt the deep mixing process the critical condition for a large oceanic response is defined by the intensity duration and timing of the ice pulse in particular as it exits through the denmark strait a recovery from this event takes several years for advection and diffusion to remove the salinity anomaly concurrently the influence of the gsa propagates to the subtropics via the boundary currents and baroclinic adjustment as a result of this adjustment there are large up to 20 changes in the strength of the overturning cell and in the meridional heat transport in the subtropics and subpolar areas simulations show a temperature sali

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

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

large scale atlantic salinity changes over the last half century a model observation comparison abstract large scale freshening of the northern atlantic and concurrent salinity increases in the low latitude atlantic upper layers have been widely reported for the second half of the twentieth century the role of anthropogenic and or unforced variability processes in these changes and the potential for the high latitude freshening to slow the atlantic meridional overturning circulation moc have been the subject of debate these issues are investigated by comparing observed and simulated changes using the third hadley centre coupled model hadcm3 this analysis suggests that a substantial part of the observed trends could be related to multidecadal variability of the moc using an sst derived proxy for historical moc changes in conjunction with model internal variability relationships suggests that much of the observed evolution of northern atlantic freshwater content can be explained as being driven by unforced moc variability hadcm3 simulations with external historical time varying forci

influence of atlantic meridional overturning circulation on the east asian winter monsoon east asian summer monsoon precipitation varied on millennial timescales during the last glacial period sediment records and climate modelling suggest that the winter monsoon was also affected by millenial scale variability and that the abrupt changes were driven by changes in the strength of the atlantic meridional overturning circulation

partial recovery of the arctic ocean halocline 1 the evolution during the 1990 s of the cold halocline layer chl of the arctic ocean is investigated using data from icebreaker and scicex submarine cruises the chl disappearance and subsequent partial recovery is described along repeated transects through the central arctic ocean from the alpha ridge to the nansen basin salinity at the top of the halocline is used as a measure of halocline development with high salinity corresponding to a poorly developed halocline in the nansen amundsen and makarov basins upper ocean salinity increased from 1991 to 1998 as the chl disappeared then decreased from 1998 to 2000 as it recovered salinity was higher over the study region through the 1990 s than at any time during the prior 40 year period hence the 1990 s chl recovery was only partial disappearance of the chl from the eurasian basin in the early 1990 s was due to a shift from the laptev to east siberian seas of the region for seaward flow of low salinity siberian shelf waters ice velocities and sea level pressure fields suggest that the reappearance of the chl in 1999 corresponded to a shift of this flow back to the laptev sea region

steric sea level change in the northern seas abstract ocean temperature and salinity data over the period 1950 2000 in the northern seas defined here as the north atlantic ocean north of 50 n north pacific ocean north of 40 n and arctic oceans are combined to diagnose the steric i e density contribution to sea level variation the individual contributions to steric height from temperature thermosteric height and salinity halosteric height are also analyzed it is found that during 1950 2000 steric height rose over the study s domain mostly as a result of halosteric increases i e freshening over a shorter time period late 1960s to early 1990s during which climate indices changed dramatically steric height gradients near the nordic seas minimum were reduced by 18 32 it is speculated that this may be associated with a local slowing of both the meridional overturning circulation and the southward flow through fram strait however steric height increases in the north pacific ocean during this time imply a possible accelerati

the canada basin 1989 1995 upstream events and far field effects of the barents sea 1 the effects of upstream events on southern canada basin waters were examined using physical and geochemical data collected at one location between 1989 and 1995 these events included atlantic layer warming relocation of the atlantic pacific water mass boundary and increased ventilation of boundary current waters early signals of change in the canada basin first appeared in 1993 along the continental margin and by 1995 were evident in the basin interior and farther downstream differences in physical and geochemical properties nutrients oxygen 129i and cfcs were observed between 150 and 1600 m of the water column by 1995 the boundary between pacific and atlantic origin water was shallower and atlantic origin water occupied more of the canada basin water column atlantic origin lower halocline water was colder and more ventilated fram strait branch water was colder fresher and more ventilated and barents sea branch water was warmer fresher more ventilated and occupied a larger volume of the water column than in previous years water mass analysis showed that the composition of atlantic origin water in the canada basin in 1995 included 20 more water from the barents sea two related events upstream appear to be the source of this change an atmospheric regime shift in 1989 that increased cyclonic circulation a transition unprecedented within the latter half of the 20th century in magnitude geographic reach and apparent oceanographic impacts and a large volume of dense water flowed from the barents sea to the arctic ocean between 1988 and 1989 these two phenomena illustrate the close relationship between atmospheric and oceanic events whose combined influence was evident 6 years later and 5100 km downstream in the canada basin at depths 1000 m

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

freshening of the labrador sea surface waters in the 1990s another great salinity anomaly 1 the observed labrador sea surface salinities for 1951 2001 in region 55w 40w 45n 55n show freshening in the 1990s which may rival the great salinity anomaly gsa of the 1970s dickson et al 1988 the 1990s freshening is distinct in the lowest range of salinity values associated with the coastal waters the variability of the highest salinity values provided by the north atlantic current entering the labrador sea shows that the high salinity atlantic waters were not widely present in the 1970 s and 1990s this can be interpreted as weakened transport of saline waters to the area this explanation is consistent with an arctic north atlantic model results forced by ncep ncar reanalysis data for 1958 2001 which suggest that these periods are associated with a reduced meridional overturning the model also associates the coastal freshening with southward current anomalies which are well correlated with the number of icebergs crossing 48n

dilution of the northern north atlantic ocean in recent decades declining salinities signify that large amounts of fresh water have been added to the northern north atlantic ocean since the mid 1960s we estimate that the nordic seas and subpolar basins were diluted by an extra 19 000 5000 cubic kilometers of freshwater input between 1965 and 1995 fully half of that additional fresh water about 10 000 cubic kilometers infiltrated the system in the late 1960s at an approximate rate of 2000 cubic kilometers per year patterns of freshwater accumulation observed in the nordic seas suggest a century time scale to reach freshening thresholds critical to that portion of the atlantic meridional overturning circulation

formation and propagation of great salinity anomalies north atlantic arctic ocean and sea ice variability for the period 1948 2001 is studied using a global ocean general circulation model coupled to a dynamic thermodynamic sea ice model forced by daily ncep ncar reanalysis data kalnay et al 1996 variability of arctic sea ice properties is analysed in particular the formation and propagation of sea ice thickness anomalies that are communicated via fram strait into the north atlantic these export events led to the great salinity anomalies gsa of the 1970s 1980s and 1990s in the labrador sea ls all gsas were found to be remotely excited in the arctic rather than by local atmospheric forcing over the ls sea ice and fresh water exports through the canadian archipelago caa are found to be only of minor importance except for the 1990s gsa part of the anomalies are tracked to the newfoundland basin where they enter the north atlantic current the experiments indicate only a minor impact of a single gsa event on the strength of the north atlantic thermohaline circulation thc

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

freshwater budget of the canada basin arctic ocean from salinity δ18o and nutrients 1 the contribution of freshwater components e g meteoric sea ice and pacific water in the canada basin is quantified using salinity 18o and nutrient data collected in 2003 and 2004 the penetration depth of sea ice meltwater is limited to the upper 30 m and brine rejected during sea ice formation is observed from 30 to 250 m depth the fraction of meteoric water is high in the upper 50 m and decreases with depth pacific water entering via bering strait is the main source of freshwater below 50 m depth bering strait throughflow which transports pacific water with salinity 32 5 together with meteoric water supplied upstream of the bering strait contributes up to 75 of freshwater input 3200 km3 a 1 to the canada basin the mean residence time of pacific water in the canada basin is estimated to be 11 years precipitation and river runoff from both north american and eurasian continents add 800 km3 a 1 and sea ice formation removes 900 km3 a 1 0 6 m a 1 of fresh water the export of ice and liquid fresh water from the canada basin contributes 40 of the freshwater flux from the arctic ocean to the north atlantic ocean

rapid freshening of the deep north atlantic ocean over the past four decades the overflow and descent of cold dense water from the sills of the denmark strait and the faroe shetland channel into the north atlantic ocean is the principal means of ventilating the deep oceans and is therefore a key element of the global thermohaline circulation most computer simulations of the ocean system in a climate with increasing atmospheric greenhouse gas concentrations predict a weakening thermohaline circulation in the north atlantic as the subpolar seas become fresher and warmer1 2 3 and it is assumed that this signal will be transferred to the deep ocean by the two overflows from observations it has not been possible to detect whether the ocean s overturning circulation is changing but recent evidence suggests that the transport over the sills may be slackening4 here we show through the analysis of long hydrographic records that the system of overflow and entrainment that ventilates the deep atlantic has steadily changed over the past four decades we find that these changes have already led to sustained and widespread freshening of the deep ocean

fram strait sea ice volume export estimated between 2003 and 2008 from satellite data 1 satellite based estimates of monthly sea ice volume exports through fram strait for the years 2003 to 2008 are presented these are obtained from individual satellite observations of sea ice thickness area and drift first sea ice freeboard is inferred from icesat laser altimeter observations and then converted to ice thickness estimates sea ice area and drift are derived from amsr e 89 ghz data retrieved sea ice thickness estimates compare within 0 5 m with the few uls data available in the fram strait the mean minimum and maximum observed monthly fram strait sea ice volume export amounts to 217 92 and 420 km3 month respectively in comparison to former fram strait sea ice volume export estimates obtained during the 1990s our estimates are slightly smaller 33 km3 month but are within the natural variability and no significant change of the total amount of fram strait sea ice export can be observed

great salinity anomalies in the north atlantic abstract we revisited the great salinity anomaly of the 1970s gsa 70s dickson et al 1988 and documented the newly identified great salinity anomaly of the 1980s hence termed gsa 80s both propagated around the north atlantic in a similar fashion the advective mechanism initially proposed to explain the observed sequence of low salinity low temperature events during the gsa 70s apparently holds also for the gsa 80s the latter was successively observed in the west greenland current 1982 the labrador current 1983 the flemish pass 1984 near the charlie gibbs fracture zone 1984 1985 in the rockall channel 1985 south of iceland 1985 1988 in the north sea 1986 1987 norwegian sea 1987 1988 barents sea 1988 1989 and iceland sea 1989 1990 the advection speed of the gsa 80s seems to be greater than the one of the gsa 70s the 1980s anomaly reached the barents sea 6 to 7 years after peaking in the west greenland current while the 1970s anomaly traveled the same route in 8 to 10 years these anomalies however seem to be of different origin the gsa 70s was apparently boosted remotely by a freshwater sea ice pulse from the arctic via fram strait consequently the gsa 70s was accompanied by a large sea ice extent anomaly in the greenland and iceland seas which propagated into the labrador sea in contrast the gsa 80s was likely formed locally in the labrador sea baffin bay mainly because of the extremely severe winters of the early 1980s but supplemented with a possible contribution of the arctic freshwater outflow via the canadian archipelago facilitated by strong northerly winds which would have enhanced stability and ice formation this anomaly was also associated with a positive sea ice extent anomaly in the labrador sea baffin bay which however had no upstream precursor in the greenland sea thus the gsas are not necessarily caused solely by an increased export of freshwater and sea ice from the arctic via fram strait these results are corroborated by the early 1990s data when a new fresh cold anomaly was formed in the labrador sea and accompanied by a large positive sea ice extent anomaly the harsh winters of the early 1990s were however confined to the labrador sea baffin bay area while the atmospheric and oceanic conditions in the greenland iceland and irminger seas were normal the labrador sea baffin bay area appears therefore to play a key role in formation of gsas as well as in propagation of the gsas formed upstream a likely contribution of the enhanced canadian archipelago freshwater outflow to the gsa formation also seems to be significant two major modes of the gsa origin are thus identified remote generated by an enhanced arctic ocean freshwater export via either fram strait or the canadian archipelago and local resulting from severe winters in the labrador sea baffin bay both modes should be taken into account to model decadal variability of the coupled ocean ice atmosphere system in the north atlantic arctic basin

hydrographic changes in the lincoln sea in the arctic ocean with focus on an upper ocean freshwater anomaly between 2007 and 2010 hydrographic data from the arctic ocean show that freshwater content in the lincoln sea north of greenland increased significantly from 2007 to 2010 slightly lagging changes in the eastern and central arctic the anomaly was primarily caused by a decrease in the upper ocean salinity in 2011 upper ocean salinities in the lincoln sea returned to values similar to those prior to 2007 throughout 2008 2010 the freshest surface waters in the western lincoln sea show water mass properties similar to fresh canada basin waters north of the canadian arctic archipelago in the northeastern lincoln sea fresh surface waters showed a strong link with those observed in the makarov basin near the north pole the freshening in the lincoln sea was associated with a return of a subsurface pacific water temperature signal although this was not as strong as observed in the early 1990s comparison of repeat stations from the 2000s with the data from the 1990s at inline image showed an increase of the atlantic temperature maximum which was associated with the arrival of warmer atlantic water from the eurasian basin satellite derived dynamic ocean topography of winter 2009 showed a ridge extending parallel to the canadian archipelago shelf as far as the lincoln sea causing a strong flow toward nares strait and likely fram strait the total volume of anomalous freshwater observed in the lincoln sea and exported by 2011 was close to inline image approximately 13 of the total estimated fw increase in the arctic in 2008

the great salinity anomaly in the northern north atlantic 1968 1982 the widespread freshening of the upper 500 800m layer of the northern north atlantic which this paper describes represents one of the most persistent and extreme variations in global ocean climate yet observed in this century though a range of explanations have been advanced to explain this event including in situ changes in the surface moisture flux this paper describes the great salinity anomaly as largely though not entirely an advective event traceable around the atlantic subpolar gyre for over 14 years from its origins north of iceland in the mid to late 1960s until its return to the greenland sea in 1981 1982 the overall propagation speed around this subpolar gyre is estimated at about 3cm s 1 of the total salt deficit associated with the anomaly as it passed south along the labrador coast in 1971 1973 about 72 109 tonnes a deficit equivalent to about two thirds of this figure 47 109 tonnes ultimately passed through the faroe shetland channel to the barents sea arctic ocean and greenland sea during the mid 1970s possible effects on deep water formation and on the representativeness of historical section data are discussed

causes and development of repeated arctic ocean warming events 1 a model hindcast for 1948 2002 shows several warming events in the atlantic layer of the arctic ocean the most recent warming event in the 1990s spread from fram strait to the lomonosov ridge and into the canadian basin only a warming event in the 1960s can also be followed into the eastern eurasian basin these two warming events are reinforced by anomalously warm flow from the barents sea while warming events in the 1970s and 1980s encounter average or below normal temperatures in the barents sea branch of the atlantic water the warm barents sea outflow in the 1960s is caused by extensive ice cover and a melt water induced halocline in the barents sea that reduced heat loss from the atlantic water in the 1990s however the warm inflow from the nordic seas was responsible for warmer than normal flow from the barents sea into the arctic ocean

arctic ocean change heralds north atlantic freshening 1 a large pool of freshwater formed of ice and runoff is hosted by the arctic ocean it exits through the canadian archipelago and fram strait to enter the north atlantic deep water production regions using a numerical model and observations we trace a strong freshwater release to subpolar waters in the mid 1990s in contrast to the ice export driven 1970 s great salinity anomaly its source was a large additional liquid freshwater release from the arctic ocean in fact it was a consequence of a change of the arctic ocean s thermohaline structure in response to the very intense north atlantic oscillation in the early 1990s our results show a strong link of large scale arctic ocean changes with the freshwater flux to subpolar waters

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

organic petrography and pore structure characterization of low mature and gas mature marine organic rich mudstones insights into porosity controls in gas shale systems analyses of both type ii organic rich low mature mudstones from the kimmeridge clay formation yorkshire england and gas mature mudstones from the vaca muerta formation argentina were performed using petrographic and sem observations to characterize the organic and inorganic components of the rocks and their relationship with porosity the porosity analyses using nitrogen adsorption measurements and mercury intrusion porosimetry were then evaluated as a function of both composition and thermal maturity despite the absence of variation in the pore size distribution and the total pore volume with maturity which is controlled by total organic carbon content toc this study demonstrates that the pore network of these marine mudstones varies considerably with thermal maturity contrary to low mature samples whose porosity depends essentially on mineral interparticle pores the porosity of thermally mature rocks is mainly influenced by organic matter hosted pores located within secondary solid bitumen organic matter om porosity which is rare in the low mature stage appears to increase during thermal maturation in response to the thermal cracking of kerogen and oil to become predominant in gas mature rocks it can therefore be considered that thermal maturation is a major process for the development of the om porosity however the om of high toc 5 5 wt gas mature samples contains smaller pores than gas mature low toc mudstones probably due to a difference in the original om composition between these high and low toc samples by analogy with the kimmeridge clay formation which is often considered as time equivalent in terms of om composition uliana et al 1999 the high toc vaca muerta samples appear to have originally contained greater proportions of oil prone amorphous om and thus a better om intrinsic quality for oil generation this difference of om composition and petroleum potential between vaca muerta marine mudstones appears to have dramatically influenced the om hosted pore genesis during maturation consistent with other studies these results show that thermal maturity is not the only process that can explain om hosted pore genesis in gas shale systems the om composition can greatly influence the evolution of this porosity during maturation organic composition and om thermal maturity may therefore have a complementary effect explaining the diversity of trends observed on porosity in natural formations

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