antarctic ice sheet melting in the southeast pacific the first oceanographic measurements across a deep channel beneath the calving front of pine island glacier reveal a sub ice circulation driven by basal melting of 10 12 m yr 1 a salt box model described here gives a melt rate similar to that of ice balance and numerical models 5 50 times higher than averages for the george vi and ross ice shelves melting is fueled by relatively warm circumpolar deep water that floods the deep floor of the amundsen and bellingshausen sea continental shelves reaching the deep draft of this floating glacier a revised melt rate for ice shelves in the southeast pacific sector raises circumpolar ice shelf melting to 756 gt yr 1 given prior estimates of surface accumulation and iceberg calving this suggests that the antarctic ice sheet is currently losing mass to the ocean

spreading of greenland meltwaters in the ocean revealed by noble gases we present the first noble gas observations in a proglacial fjord in greenland providing an unprecedented view of surface and submarine melt pathways into the ocean using optimum multiparameter analysis noble gas concentrations remove large uncertainties inherent in previous studies of meltwater in greenland fjords we find glacially modified waters with submarine melt concentrations up to 0 66 0 09 and runoff 3 9 0 29 radiogenic enrichment of helium enables identification of ice sheet near bed melt 0 48 0 08 we identify distinct regions of meltwater export reflecting heterogeneous melt processes a surface layer of both runoff and submarine melt and an intermediate layer composed primarily of submarine melt intermediate ocean waters carry the majority of heat to the fjords glaciers and warmer deep waters are isolated from the ice edge the average entrainment ratio implies that ocean water masses are upwelled at a rate 30 times the combined glacial meltwater volume flux

modeling the formation and deposition of frazil ice beneath filchner ronne ice shelf large areas of the filchner ronne ice shelf are underlain by layers of marine ice which form when supercooled seawater circulating beneath the ice shelf freezes the freezing process initially produces a suspension of disc shaped frazil ice crystals and these are subs quently deposited onto the ice shelf base in areas where the flow of water is slack enough this has been modeled assuming that the freezing takes place within buoyant plumes of ice shelf water ascending the ice shelf base from source regions near the grounding lines of the major inlet glaciers the deposition of the majority of the suspended frazil ice is found to occur in spatially discrete bursts where peak rates of accumulation at the ice shelf base exceed 1 m yr 1 of solid ice there is a good correlation between the location of the zones of crystal deposition and the position of the upstream limits of the marine ice layers the high rates of localized accumulation account for the rapid buildup observed in the layer thickness which then gradually declines as the marine ice is carried downstream with the flow of the ice shelf model results also suggest an origin for the ice platelets observed at depth in the water column near the filchner ice shelf

isotope data from ice station weddell implications for deep water formation in the weddell sea helium isotope data 3he 4he ratios and 4he concentrations and h218o h216o ratios obtained from stations occupied during the drift of ice station weddell february to june 1992 are used together with hydrographic data to study formation of deep and bottom water in the western weddell sea the data indicate deep and bottom water formation along the entire track of the ice station 71 4 to 65 8 s 53 w ice shelf water isw seems to contribute significantly to the formation of weddell sea deep water wsdw and weddell sea bottom water wsbw in the southern part of the drift track toward the north the fraction of isw contained in wsdw wsbw decreases this trend is overlaid by high isw fractions in the deep and bottom waters found in the vicinity of the larsen ice shelf the fraction of western shelf water wsw in wsbw shows the opposite trend increasing from south to north the combined fraction of isw and wsw in waters with potential temperatures below 0 c is about 20 corresponding to a roughly 200 m thick layer overall wsw seems to contribute approximately 2 to 3 times more water than isw to the water column below the 0 c isotherm using the estimated flow of isw over the sill north of the filchner depression of 1 sv foldvik et al 1985a together with the ratio of wsw plus winter water ww to isw we calculate a value of about 5 sv for the formation rate of wsbw with a potential temperature of 0 7 c about one third of this flux represents near surface waters wsw ww which have recently been equilibrated with the atmosphere whereas pure isw contributes about 10

freshening of the ross sea during the late 20th century ocean measurements in the ross sea over the past four decades one of the longest records near antarctica reveal marked decreases in shelf water salinity and the surface salinity within the ross gyre these changes have been accompanied by atmospheric warming on ross island ocean warming at depths of 300 meters north of the continental shelf a more negative southern oscillation index and thinning of southeast pacific ice shelves the freshening appears to have resulted from a combination of factors including increased precipitation reduced sea ice production and increased melting of the west antarctic ice sheet

upper ocean distribution of glacial meltwater in the amundsen sea antarctica pine island ice shelf in the amundsen sea is losing mass due to increased heat transport by warm ocean water penetrating beneath the ice shelf and causing basal melt tracing this warm deep water and the resulting glacial meltwater can identify changes in melt rate and the regions most affected by the increased input of this freshwater here optimum multi parameter analysis is used to deduce glacial meltwater fractions from independent water mass characteristics standard hydrographic observations noble gases and oxygen isotopes collected during a ship based campaign in the eastern amundsen sea in february march 2014 noble gases neon argon krypton and xenon and oxygen isotopes are used to trace the glacial melt and meteoric water found in seawater and we demonstrate how their signatures can be used to rectify the hydrographic trace of glacial meltwater which provides a much higher resolution picture the presence of glacial meltwater is shown to mask the winter water properties resulting in differences between the water mass analyses of up to 4 g kg 1 glacial meltwater content this discrepancy can be accounted for by redefining the pure winter water endpoint in the hydrographic glacial meltwater calculation the corrected glacial meltwater content values show a persistent signature between 150 400 m of the water column across all of the sample locations up to 535 km from pine island ice shelf with increased concentration towards the west along the coastline it also shows for the first time the signature of glacial meltwater flowing off shelf in the eastern channel

cmip5 temperature biases and 21st century warming around the antarctic coast projections of ice sheet mass balance require regional ocean warming projections derived from atmosphere ocean general circulation models aogcms however the coarse resolution of aogcms 1 may lead to systematic or aogcm specific biases and 2 makes it difficult to identify relevant water masses here we employ a large scale metric of antarctic shelf bottom water asbw to investigate circum antarctic temperature biases and warming projections in 19 different coupled model intercomparison project phase 5 cmip5 aogcms forced with two different representative concentration pathways rcps for high emissions rcp 8 5 the ensemble mean 21st century asbw warming is 0 66 0 74 and 0 58 c for the amundsen ross and weddell seas as rs and ws respectively rcp 2 6 ensemble mean projections are substantially lower 0 21 0 26 and 0 19 c all distributions of regional asbw warming are positively skewed for rcp 8 5 four aogcms project warming of greater than 1 8 c in the rs across the ensemble there is a strong rcp independent correlation between ws and rs warming as warming is more closely linked to warming in the southern ocean we discuss possible physical mechanisms underlying the spatial patterns of warming and highlight implications of these results on strategies for forcing ice sheet mass balance projections

optimum multiparameter analysis of mixing in the thermocline of the eastern indian ocean a method of water mass analysis is developed which optimizes the use of all information contained in a hydrographic data set by solving an overdetermined linear set of mixing equations it requires representation of water masses by a finite number of water types and observations from at least as many oceanographic parameters as water types the procedure to establish the water types find the correct weights for the parameters and solve the mixing equations through minimization of the residuals is described in detail the method is applied to a data set from the eastern indian ocean where indian central water and australasian mediterranean water meet to produce a strong front in the thermocline it is shown that although most of the water from the indonesian archipelago is carried westward north of 11 s contributions from the australasian mediterranean water are found as far south as 25 s particularly along the australian shelf as a result of advection with the leeuwin current

an optimized estimate of glacial melt from the ross ice shelf using noble gases stable isotopes and cfc transient tracers 1 isotopes of helium and neon and the h218o h216o ratio of water are proven proxies for melt from glacial ice beneath floating ice shelves and at ice shelf fronts their high concentrations in glacial meltwater compared to other environmental sources make them ideal tracers for studies of the pathways of glacial meltwater from its origins into the ocean interior we combine noble gas and stable isotopes with temperature salinity and dissolved oxygen measurements from three cruises along the ross ice shelf during the austral summers of 1993 1994 and 1999 2000 and to the ross sea in 2000 2001 and use optimal multiparameter analysis to compute the water mass concentration including glacial meltwater the distribution of meltwater at the front of the ross ice shelf extended east from 180 w with the highest concentrations found near 165 w in both 1994 and 2000 the mean meltwater concentration at the ice shelf front was 2 0 0 33 in 1994 2 2 0 36 in 2000 and 0 25 0 1 in the western ross sea in 2001 water mass concentrations are used to correct for bias in the cfc age introduced by mixing with cfc free waters an effect revealed by comparing cfc age with transit time distribution curves the water residence time within the ice shelf cavity using cfcs and the mean meltwater concentration implies a basal melt rate of 33 50 km3 a 1

excess helium and neon in the southeast pacific tracers for glacial meltwater 1 we analyze helium he and neon ne isotope data sets from the southeast pacific sector of the southern ocean collected in 1992 and 1994 and describe a new method to estimate glacial meltwater fluxes independent of previous approaches the waters sampled during these cruises reveal large atmospheric he and ne excess concentrations in the upper 500 m that are derived predominantly from the dissolution of air contained in glacial ice during melting underneath and at the front of floating ice shelves at elevated hydrostatic pressure on the stations sampled the meltwater fractions are largest near the northern and southern ice shelf fronts of george vi ice shelf 1 5 2 5 consistent with prior inferences from 18o the inventories of 4he and ne with local glacial meltwater origin south of 70 s between 210 e and 295 e are 2 5 0 7 1011 cm3stp 4he and 7 9 2 7 1011 cm3stp ne respectively the associated meltwater volumes are 430 120 gt for 4he and 400 140 gt for ne for an estimated seawater residence time of 2 years on the continental shelf the amounts of glacial meltwater translate into bulk melting rates of 215 170 gt yr 1 for 4he and 200 170 gt yr 1 for ne the values derived from 4he are expected to be larger than those obtained from ne because of the terrigenic he component which accounts for 10 15 of the he excess in this region our regional melting rate of 200 215 gt yr 1 is comparable to a prior estimate but subject to uncertainties resulting from the station distribution the air sea gas exchange and the estimate of the net transport through the study region

circulation and melting beneath george vi ice shelf antarctica introduction george vi ice shelf sandwiched between the western coast of palmer land and the eastern coast of alexander island is the largest and most studied of the west antarctic peninsula ice shelves it covers an area of approximately 25 000 km2 and is underlain by circumpolar deep water cdw with temperatures in excess of 1oc giving rise to rapid basal melting bishop and walton 1981 lennon et al 1982 the maximum ice thickness of about 500 m occurs about 70 km from the southern ice front where a ridge of thick ice extends across george vi sound near 70ow see figure 1 effectively dividing the upper water column into northern and southern regions the northern ice front which faces marguerite bay appears to be near the geographical limit of ice shelf viability and has undergone a gradual retreat in recent decades lucchitta and rosanova 1998 a timeframe over which much of the nearby wordie ice shelf disintegrated doake and vaughan 1991 there is extensive surface melting over the northern parts of the ice shelf and much of the ice column near the northern ice front appears to be temperate paren and cooper 1986 conditions in the south where the ice front faces into ronne entrance are colder and the ice front position appears to be steady the vast majority of the flow into the ice shelf comes from palmer land but basal melting is sufficient to remove most of this so that the ice is derived almost exclusively from local accumulation by the time it reaches the ice fronts potter et al 1984 there is some evidence at the margins of the ice shelf to suggest that it may have disappeared completely during the early holocene before reforming sugden and clapperton 1981 bentley et al 2005

ice velocity mapping of ross ice shelf antarctica by matching surface undulations measured by icesat laser altimetry abstract we present a novel method for estimating the surface horizontal velocity on ice shelves using laser altimetry data from the ice cloud and land elevation satellite icesat 2003 2009 the method matches undulations measured at crossover points between successive campaigns elevation measurements are first relocated into a time varying moving coordinate system using an initial velocity e g from velmap and then crossover height differences are minimized with an adjustment vector errors in geolocation of the icesat tracks result in some error in the adjustment vectors but these are small relative to the velocity adjustment for fast moving ice shelves we use the algorithm to estimate changes in the ice velocity of ross ice shelf between an earlier mapping from velmap and the icesat period the new velocity field is compared with velocities from in situ measurements and satellite radar interferometry the slowdown of 98 34 m yr 1 23 is observed in the ice shelf downstream of whillans ice stream and the deceleration rate is 3 1 1 1 m yr 2 during last three decades the method can be expanded to the simultaneous mapping of ice horizontal velocity ice thickness change and surface deformation for antarctic ice shelves as well as a more accurate mapping using future icesat 2 measurements

helium a new tracer in antarctic oceanography the abyssal characteristics of the world oceans are strongly influenced by the northward propagation of antarctic bottom water aabw an important source of aabw is weddell sea bottom water wsbw which is formed in part on the continental slope of the southern weddell sea1 3 the formation of wsbw on the continental slope is related to the floating ice shelves of the southern weddell sea filchner ronne ice shelves western shelf water wsw is modified under the ice shelves by cooling and admixture of melt water to form ice shelf water isw and a substantial part of the isw flows over the sill that separates the filchner depression from the weddell sea and participates in the formation of wsbw4 5 the data reported here demonstrate that the water ice interaction leads to a strong 4he supersaturation of the isw due to dissolution of air entrapped in the ice shelf melt water the 4he supersaturation of the isw can be used as a tracer of this water mass and also influences the 4he balance of the wsbw

modeling thermodynamic ice ocean interactions at the base of an ice shelf abstract models of ocean circulation beneath ice shelves are driven primarily by the heat and freshwater fluxes that are associated with phase changes at the ice ocean boundary their behavior is therefore closely linked to the mathematical description of the interaction between ice and ocean that is included in the code an hierarchy of formulations that could be used to describe this interaction is presented the main difference between them is the treatment of turbulent transfer within the oceanic boundary layer the computed response to various levels of thermal driving and turbulent agitation in the mixed layer is discussed as is the effect of various treatments of the conductive heat flux into the ice shelf the performance of the different formulations that have been used in models of sub ice shelf circulation is assessed in comparison with observations of the turbulent heat flux beneath sea ice formulations that include an explicit parameterization of the oceanic boundary layer give results that

characteristics of meltwater export from jakobshavn isbrae and ilulissat icefjord jakobshavn isbrae which terminates in ilulissat icefjord has undergone rapid retreat and is currently the largest contributor to ice sheet mass loss among greenland s marine terminating glaciers accelerating mass loss is increasing fresh water discharge to the ocean which can feed back on ice melt impact marine ecosystems and potentially modify regional and larger scale ocean circulation here we present hydrographic observations including inert geochemical tracers that allow the first quantitative description of the glacially modified waters exported from the jakobshavn icefjord system observations within the fjord suggest a deep reaching overturning cell driven by glacial buoyancy forcing modified waters containing submarine meltwater up to 2 5 0 12 subglacial discharge up to 6 0 37 and large portions of entrained ocean waters are seen to exit the fjord and flow north the exported meltwaters form a buoyant coastal gravity current reaching to 100 m depth and extending 10 km offshore

rapid bottom melting widespread near antarctic ice sheet grounding lines as continental ice from antarctica reaches the grounding line and begins to float its underside melts into the ocean results obtained with satellite radar interferometry reveal that bottom melt rates experienced by large outlet glaciers near their grounding lines are far higher than generally assumed the melting rate is positively correlated with thermal forcing increasing by 1 meter per year for each 0 1 c rise in ocean temperature where deep water has direct access to grounding lines glaciers and ice shelves are vulnerable to ongoing increases in ocean temperature

influence of sea ice cover and icebergs on circulation and water mass formation in a numerical circulation model of the ross sea antarctica 1 satellite imagery shows that there was substantial variability in the sea ice extent in the ross sea during 2001 2003 much of this variability is thought to be due to several large icebergs that moved through the area during that period the effects of these changes in sea ice on circulation and water mass distributions are investigated with a numerical general circulation model it would be difficult to simulate the highly variable sea ice from 2001 to 2003 with a dynamic sea ice model since much of the variability was due to the floating icebergs here sea ice concentration is specified from satellite observations to examine the effects of changes in sea ice due to iceberg c 19 simulations were performed using either climatological ice concentrations or the observed ice for that period the heat balance around the ross sea polynya rsp shows that the dominant term in the surface heat budget is the net exchange with the atmosphere but advection of oceanic warm water is also important the area average annual basal melt rate beneath the ross ice shelf is reduced by 12 in the observed sea ice simulation the observed sea ice simulation also creates more high salinity shelf water another simulation was performed with observed sea ice and a fixed iceberg representing b 15a there is reduced advection of warm surface water during summer from the rsp into mcmurdo sound due to b 15a but a much stronger reduction is due to the late opening of the rsp in early 2003 because of c 19

seismic profiling the continental lithosphere deep seismic reflection profiling is successfully being used worldwide to study the structure of the continental crust1 7 the moist8 profile recorded by birps british institutions reflection profiling syndicate was the first to show that the structure of the upper mantle could also be imaged given a powerful source and long recording times birps has recently acquired an ultra deep seismic reflection line drum deep reflections from the upper mantle the drum line was designed specifically to investigate the reflectivity of the lower continental lithosphere and was therefore recorded to a two way time twt of 30 s giving a depth of penetration into the lithosphere of 110 km this profile has now revealed strong reflections which are unequivocally from the lower lithosphere well below the base of the crust and which are as far as we are aware the deepest and most continuous structures imaged in the upper mantle by multi channel seismic reflection profiling

on the scalability of hydrogeochemical factors controlling arsenic mobility in three major inland basins of p r china abstract high as groundwater has been widely found in inland basins of p r china which has posed a serious health risk to the local residents although these inland basins experience the same arid to semiarid climate and are filled with quaternary sediments as concentrations show big variations three inlands basins have been investigated to characterize hydraulic conductivities and geochemistry of the groundwater and sediments and evaluate their controls on dissolved as concentrations dissolved as concentrations ranged between

antarctic bottom water production and export by tides in the ross sea 1 current measurements in the western ross sea show that antarctic bottom water is produced at the outer edge of the continental shelf by tidal stirring of antarctic surface water circumpolar deep water and shelf water current amplitudes during spring tides are greater than 1 m s sufficient to carry circumpolar deep water onto the shelf from offshore and stir at least the lower portion of the water column to a nearly homogeneous mixture the antarctic bottom water produced every day during spring tides does not appear to have a seasonal signal its export rate is estimated to be 1 95 1 85 10 6 m 3 s

the effect of atmospheric forcing resolution on delivery of ocean heat to the antarctic floating ice shelves abstractoceanic melting at the base of the floating antarctic ice shelves is now thought to be a more significant cause of mass loss for the antarctic ice sheet than iceberg calving in this study a 10 km horizontal resolution circum antarctic ocean sea ice ice shelf model based on the regional ocean modeling system roms is used to study the delivery of ocean heat to the base of the ice shelves the atmospheric forcing comes from the era interim reanalysis 80 km resolution and from simulations using the polar optimized weather research and forecasting model 30 km resolution where the upper atmosphere was relaxed to the era interim reanalysis the modeled total basal ice shelf melt is low compared to observational estimates but increases by 14 with the higher resolution winds and just 3 with both the higher resolution winds and atmospheric surface temperatures the higher resolution winds lead to more heat being delivered to the ice shelf cavities from the adjacent ocean and an increase in the

pathways of basal meltwater from antarctic ice shelves a model study we investigate spreading pathways of basal meltwater released from all antarctic ice shelves using a circumpolar coupled ice shelf sea ice ocean model that reproduces major features of the southern ocean circulation including the antarctic circumpolar current acc several independent virtual tracers are used to identify detailed pathways of basal meltwaters the spreading pathways of the meltwater tracers depend on formation sites because the meltwaters are transported by local ambient ocean circulation meltwaters from ice shelves in the weddell and amundsen bellingshausen seas in surface subsurface layers are effectively advected to lower latitudes with the acc although a large portion of the basal meltwaters is present in surface and subsurface layers a part of the basal meltwaters penetrates into the bottom layer through active dense water formation along the antarctic coastal margins the signals at the seafloor extend along the topography showing a horizontal distribution similar to the observed spreading of antarctic bottom water meltwaters originating from ice shelves in the weddell and ross seas and in the indian sector significantly contribute to the bottom signals a series of numerical experiments in which thermodynamic interaction between the ice shelf and ocean is neglected regionally demonstrates that the basal meltwater of each ice shelf impacts sea ice and or ocean thermohaline circulation in the southern ocean

energetic plumes over the western ross sea continental slope rapid descent of dense drygalski trough western ross sea antarctica shelf water over the continental slope within 100 to 250 m thick benthic plumes is described speeds of up to 1 0 m s are recorded flowing at an average angle of 35 to the isobaths entraining ambient lower circumpolar deep water en route this process is predominant in determining the concentration and placement of the shelf water injected into the deep sea as a precursor antarctic bottom water nonetheless a 4 hour duration pulse of undiluted shelf water was observed at depth 1407 m directly north of the drygalski trough moving at around 90 degrees to isobaths and at a speed of 1 4 m s thus the export of ross sea shelf water to the deep sea is accomplished within plumes descending at moderate angle to isobaths punctuated by rapid downhill cascades

the supply of subglacial meltwater to the grounding line of the siple coast west antarctica recent satellite studies have shown that active subglacial lakes exist under the antarctic ice streams and persist almost to their grounding lines when the lowest lying lakes flood the water crosses the grounding line and enters the sub ice shelf cavity modeling results suggest that this additional freshwater influx may significantly enhance melting at the ice shelf base we examine the spatial and temporal variability in subglacial water supply to the grounding lines of the siple coast ice streams by combining estimates for lake volume change derived from ice cloud and land elevation satellite icesat data with a model for subglacial water transport our results suggest that subglacial outflow tends to concentrate towards six embayments in the siple coast grounding line although mean grounding line outflow is 60m3 s 1 for the entire siple coast maximum local grounding line outflow may temporarily exceed 300 m3 s 1 during the synchronized flooding of multiple lakes in a hydrologic basin variability in subglacial outflow due to subglacial lake drainage may account for a substantial portion of the observed variability in freshwater flux out of the ross ice shelf cavity the temporal variability in grounding line outflow results in a net reduction in long term average melt rate but temporary peak melting rates may exceed the long term average by a factor of three

melting and freezing beneath filchner ronne ice shelf antarctica 1 we use remote sensing data sets to evaluate the spatial distribution of melt beneath the filchner ronne ice shelf fris the net melt rate of 83 4 24 8 gtons yr is 2 5 5 times lower than previous glaciological estimates but is similar to existing oceanographic estimates the spatial distribution however differs significantly from standard conceptual and numerical models in which most melt occurs along the grounding lines our results suggest most grounding line melt is refrozen while the dominant ice shelf water isw source is melting near the ice shelf front probably associated with tidal action this suggests that changes in ice shelf extent can impact isw production rates in the weddell sea

oxygen 18 and helium as tracers of ice shelf water and water ice interaction in the weddell sea oxygen 18 and helium isotope data from stations located in the filchner depression on the continental slope of the southern weddell sea and in the central weddell sea are presented and discussed the 18o and 4he signals imprinted on the water circulating under the filchner ronne ice shelf ice shelf water or isw due to melting of glacial ice at the base of the ice shelf are traced across the sill separating the filchner depression from the weddell sea low 18o values are correlated with high 4he concentrations in the isw found in the filchner depression minimum 18o values 0 8 maximum 4he concentrations about 4 7 10 8 cm3 stp g 1 the fraction of glacial meltwater contained in the isw found in the filchner depression is estimated to about 6 to 7 the 18o and helium isotope data from the overflowing shelf water component observed on the continental slope confirm the hypothesis that isw contributes significantly to the weddell sea bottom water wsbw on the basis of a inultiparameter water mass analysis it is discussed which fraction of the wsbw originates from isw and which other shelf waters potentially could contribute to wsbw

mass balance of polar ice sheets recent advances in the determination of the mass balance of polar ice sheets show that the greenland ice sheet is losing mass by near coastal thinning and that the west antarctic ice sheet with thickening in the west and thinning in the north is probably thinning overall the mass imbalance of the east antarctic ice sheet is likely to be small but even its sign cannot yet be determined large sectors of ice in southeast greenland the amundsen sea embayment of west antarctica and the antarctic peninsula are changing quite rapidly as a result of processes not yet understood

a tracer study of ventilation in the japan east sea during the circulation research in east asian marginal seas creams summer cruises in 1999 a suite of samples was collected for tracer analysis oxygen isotopes combined with tritium helium ventilation timescales and noble gas measurements give unique insights into the ventilation of water masses in the japan east sea jes in particular noble gases and oxygen isotopes are indicators of brine rejection which may assist in explaining the recent changes observed in the ventilation of the jes oxygen isotope data presented here indicate that both thermally driven convection and brine rejection have played significant roles in deep water formation but that brine rejection is unlikely to be a significant contributor at the moment a 6 box ventilation model of the jes calibrated with tritium and helium 3 measurements performed better when a significant decrease of dense water formation rates in the mid 1960s was incorporated however the model calculations suggest that japan sea intermediate water formation is still occurring subduction of sea ice melt water may be a significant ventilation mechanism for this water mass based on an argon saturation minimum at the recently ventilated salinity minimum in the northwestern sector of the jes the salinity and oxygen isotope budgets imply a potential bottom water formation rate of 3 97 0 89 1012 m3 yr 1 due to brine rejection which could account for a time averaged fraction of between 25 and 35 of the ventilation of subsurface water formation in the jes