influence of permafrost distribution on groundwater flow in the context of climate driven permafrost thaw example from yukon flats basin alaska united states 1 understanding the role of permafrost in controlling groundwater flow paths and fluxes is central in studies aimed at assessing potential climate change impacts on vegetation species habitat biogeochemical cycling and biodiversity recent field studies in interior alaska show evidence of hydrologic changes hypothesized to result from permafrost degradation this study assesses the hydrologic control exerted by permafrost elucidates modes of regional groundwater flow for various spatial permafrost patterns and evaluates potential hydrologic consequences of permafrost degradation the yukon flats basin yfb a large 118 340 km2 subbasin within the yukon river basin provides the basis for this investigation model simulations that represent an assumed permafrost thaw sequence reveal the following trends with decreasing permafrost coverage 1 increased groundwater discharge to rivers consistent with historical trends in base flow observations in the yukon river basin 2 potential for increased overall groundwater flux 3 increased spatial extent of groundwater discharge in lowlands and 4 decreased proportion of suprapermafrost shallow groundwater contribution to total base flow these trends directly affect the chemical composition and residence time of riverine exports the state of groundwater influenced lakes and wetlands seasonal river ice thickness and stream temperatures presently the yfb is coarsely mapped as spanning the continuous discontinuous permafrost transition that model analysis shows to be a critical threshold thus the yfb may be on the verge of major hydrologic change should the current permafrost extent decrease this possibility underscores the need for improved characterization of permafrost and other hydrogeologic information in the region via geophysical techniques remote sensing and ground based observations

iron and humic type fluorescent dissolved organic matter in the chukchi sea and canada basin of the western arctic ocean 1 the concentrations of dissolved fe d fe total dissolvable fe t fe humic type fluorescence intensity humic f intensity as humic type fluorescent dissolved organic matter and nutrients were vertically determined in the shelf slope and basin regions chukchi sea and canada basin of the western arctic ocean during 1 27 september 2008 in all stations the remarkably high d fe and humic f intensity were found at depths between 25 and 200 m with the subsurface maxima of d fe 1 0 3 2 nm and humic f intensity 4 5 quinine sulfate units in the upper halocline layer upper hl being associated with a prominent nutrient maximum the high d fe and humic f intensity within the upper hl are probably attributed to the fe iii complexation with natural organic ligands such as marine dissolved humic substances resulting from main processes of the brine rejection during sea ice formation and interactions with sediments on the shelves however subsurface maxima 10 50 nm of t fe were found in the lower halocline layer beneath the upper hl of all slope and basin regions and are mainly attributed to the resuspension of sedimentary particles in the shelf region the finding of subsurface iron maxima in the halocline water of all regions may be the first confirmation for the lateral iron transport into the halocline layer from the shelves to the arctic basin

aspects of the marine nitrogen cycle of the chukchi sea shelf and canada basin abstract as a highly productive seasonally ice covered sea with an expansive shallow continental shelf the chukchi sea fuels high rates of sedimentary denitrification this contributes to its fixed nitrogen n deficit relative to phosphorus p which is among the largest in the global ocean making the chukchi sea severely n limited during the phytoplankton growth season here we examine aspects of the n cycle on the chukchi sea shelf and the downstream canada basin using nutrients dissolved oxygen o 2 and the stable isotopes of nitrate no 3 in the northward flow path across the chukchi shelf bottom waters experienced strong o 2 drawdown from which we calculated a nitrification rate of 1 3 mmol m 2 d 1 this nitrification was likely primarily in sediments and directly fueled sedimentary denitrification historically measured at similar rates we observed significant accumulations of ammonium nh 4 in bottom waters of the chukchi shelf up to 5 m which were inversely correlated with 15 n no 3 indicating a sediment source of 15 n enriched nh 4 this is consistent with a process of coupled partial nitrification denitrification cpnd which imparts significant 15 n enrichment and 18 o depletion to pacific origin no 3 this cpnd mechanism is consistent with a significant decrease in 18 o no 3 relative to bering sea source waters indicating that at least 58 of no 3 populating the pacific halocline was regenerated during its transit across the north bering and chukchi shelves rather than arriving preformed from the bering sea slope this pacific origin no 3 propagates into the canada basin and towards the north atlantic being significantly 15 n enriched and 18 o depleted relative to the underlying atlantic waters

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

trace metals and organic carbon in sediments of the northeastern chukchi sea abstract concentrations of al fe and selected trace metals as ba be cd cr cu hg mn ni pb sb se sn v zn in surface sediments from the northeastern chukchi sea necs varied considerably as a function of sediment texture i e grain size however essentially all metals when normalized to al were present at natural background values total organic carbon content ranged from 0 06 1 56 with a marine origin for at least two thirds of the organic matter at each station based on 13c values and c n ratios recent sedimentation rates from 137cs and 210pb dating were 0 03 0 14 cm yr 1 corresponding vertical distributions for most metals in age dated sediment cores showed 100 yr records of uniform metal al ratios including pb and hg concentrations of as mn and cd were modified in surface sediments at a few stations by early chemical diagenesis surveys around two exploratory oil and gas drilling sites that were occupied in 1989 showed that ba concentrations were as high as 10 000 g g 1 within 200 m of one drilling site relative to background values of 700 g g 1 barium enrichment was from barite a drilling mud additive that was discharged to the seafloor above background concentrations of cu hg pb and zn also were found in sediments from 3 4 stations within 200 m of the two drilling sites at present sediments in the necs are essentially pristine with respect to trace metals of anthropogenic origin excluding small areas around drilling sites these data should be of value for detecting and tracking future chemical changes in the sediments of the necs particularly in light of planned oil and gas exploration and production as well as environmental changes that may be associated with climate change

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

observational and modeling evidence of seasonal trends in sediment derived material inputs to the chukchi sea author posting american geophysical union 2020 this article is posted here by permission of american geophysical union for personal use not for redistribution the definitive version was published in journal of geophysical research oceans 125 5 2020 e2019jc016007 doi 10 1029 2019jc016007

winter currents and hydrographic conditions on the northern central bering sea shelf current observations obtained from the northern bering shelf region in winter 1984 1985 indicate that midwinter circulation patterns differed from those during the rest of the year annual mean circulation in this region is dominated by vigorous northward currents from 10 cm s in shpanberg strait to more than 50 cm s in bering strait these northward currents are accompanied by a weak northwestward coastal flow south of st lawrence island in february april 1985 however flow was weakly 0 5 cm s southward through shpanberg strait and southeastward south of st lawrence island while remaining northward through anadyr and bering straits comparison with current data obtained from previous years suggests that midwinter reversal of flow in shpanberg strait is a recurrent winter feature it generally occurs at about the same time that the winter ice cover undergoes its major advance and it is associated with strong northerly winds northward flow through anadyr strait persists conversely through the winter and is the northward extension of a western intensified northward flow over the bering shelf its source is bering sea water farther south rather than water from the northern central shelf the resultant trapping of shelf water on the northern central shelf coupled with intensive regional ice formation during the same period as the flow reversal led in 1985 to significant about 1 5 brine enrichment this salinity increase agrees qualitatively with historical data which suggest that the northern central bering shelf is the site both of sluggish winter circulation and of elevated salinities due to brine enrichment from ice formation

evaluation of shelf basin interaction in the western arctic by use of short lived radium isotopes the importance of mesoscale processes shelf basin exchange in the western arctic was evaluated by use of water column analyses of 228 ra 226 ra ratios and the first measurements of the short lived 224 ra t1 2 3 64 d in the arctic during the 2002 shelf basin interaction sbi program excess 224 ra was detected over the shelf but was not found seaward of the shelf break similarly the 228 ra 226 ra ratio dropped rapidly from the shelf across the shelf break consequently the model age gradient elapsed time since shelf residence northward across the chukchi shelf increased from 1 5 years nearshore to approximately 14 years in surface waters sampled off shelf at the southern margin of the beaufort gyre this steep gradient is consistent with very slow exchange between the chukchi shelf and the beaufort gyre whereby bering strait inflow is constrained by the earth s rotation to follow local isobaths and does not easily move into deeper water the strong dynamic control inhibiting water that enters the system through bering strait from flowing north across isobaths also would lead to a long recirculation time of river water emptied into the beaufort gyre possible mechanisms that can generate cross shelf currents that break the topographic constraint to follow isobaths and thereby transport water and associated properties off the shelves include wind induced upwelling downwelling meandering jets and eddies evidence of such a process was found during the icex project in the beaufort sea in april 2003 when excess 224 ra was measured over 200 km from any shelf source this required an ne offshore flow of 40 cm s 1 assuming that the source water derives from the mouth of barrow canyon a weak northeastward flow was measured using an ladcp within the upper 300 m of the ocean but was of lower speed than required by the 224 raxs at the time of the icex occupation

circulation and water mass transformation in a model of the chukchi sea 1 the circulation and water mass transformation in a regional ocean ice model of the chukchi sea are discussed the model has horizontal resolution of o 4 km is forced by fluxes derived from daily ncep reanalysis fields and has seasonally varying transport temperature and salinity imposed at bering strait many of the observed characteristics of the mean circulation and seasonal cycle in the chukchi sea are reproduced the discussion focuses on the branching of the inflow transport into pathways following herald canyon central channel and the alaskan coast the pattern of ice melt and the water mass transformation and formation of winter water and hypersaline water the ice melt pattern and timing is strongly influenced by advection through bering strait high frequency forcing results in a larger region of ice melt particularly over the shoals and in the northern chukchi sea compared to monthly mean forcing in the model the seasonal cycle of salinity in the southern and central chukchi sea is dominated by advection through bering strait while local atmospheric forcing and brine rejection are more important north of herald and hanna shoals and in barrow canyon however since the residence time in the chukchi sea is generally less than 1 year interannual variability in the bering strait salinity will be reflected in the salinity across the chukchi sea and at barrow canyon

circulation on the north central chukchi sea shelf abstract mooring and shipboard data collected between 1992 and 1995 delineate the circulation over the north central chukchi shelf previous studies indicated that pacific waters crossed the chukchi shelf through herald valley in the west and barrow canyon in the east we find a third branch through the central channel onto the outer shelf the central channel transport varies seasonally in phase with bering strait transport and is 0 2 sv on average although some of this might include water entrained from the outflow through herald valley a portion of the central channel outflow moves eastward and converges with the alaskan coastal current at the head of barrow canyon the remainder appears to continue northeastward over the central outer shelf toward the shelfbreak joined by outflow from herald valley the mean flow opposes the prevailing winds and is primarily forced by the sea level slope between the pacific and arctic oceans current variations are mainly wind forced but baroclinic forcing associated with upstream dense water formation in coastal polynyas might occasionally be important winter water mass modification depends crucially on the fall and winter winds which control seasonal ice development an extensive fall ice cover delays cooling limits new ice formation and results in little salinization in such years bering shelf waters cross the chukchi shelf with little modification in contrast extensive open water in fall leads to early and rapid cooling and if accompanied by vigorous ice production within coastal polynyas results in the production of high salinity 33 shelf waters such interannual variability likely affects slope processes and the transport of pacific waters into the arctic ocean interior

shelf basin exchange times of arctic surface waters estimated from 228th 228ra disequilibrium the transpolar drift is strongly enriched in 228ra accumulated on the wide arctic shelves with subsequent rapid offshore transport we present new data of polarstern expeditions to the central arctic and to the kara and laptev seas because 226ra activities in pacific waters are 30 higher than in atlantic waters we correct 226ra for the pacific admixture when normalizing 228ra with 226ra the use of 228ra decay as age marker critically depends on the constancy in space and time of the source activity a condition that has not yet adequately been tested while 228ra decays during transit over the central basin ingrowth of 228th could provide an alternative age marker the high 228th 228ra activity ratio ar 0 8 1 0 in the central basins is incompatible with a mixing model based on horizontal eddy diffusion an advective model predicts that 228th grows to an equilibrium ar the value of which depends on the scavenging regime the low ar over the lomonosov ridge ar 0 5 can be due to either rapid transport minimum age without scavenging 1 1 year or enhanced scavenging suspended particulate matter load derived from beam transmission and particulate 234th and total 234th depletion data show that scavenging although extremely low in the central arctic is enhanced over the lomonosov ridge making an age of 3 years more likely the combined data of 228ra decay and 228th ingrowth confirm the existence of a recirculating gyre in the surface water of the eastern eurasian basin with a river water residence time of at least 3 years

interpreting u pb data from primary and secondary features in lunar zircon in this paper we describe primary and secondary microstructures and textural characteristics found in lunar zircon and discuss the relationships between these features and the zircon u pb isotopic systems and the significance of these features for understanding lunar processes lunar zircons can be classified according to i textural relationships between zircon and surrounding minerals in the host breccias ii the internal microstructures of the zircon grains as identified by optical microscopy cathodoluminescence cl imaging and electron backscattered diffraction ebsd mapping and iii results of in situ ion microprobe analyses of the th u pb isotopic systems primary zircon can occur as part of a cogenetic mineral assemblage lithic clast or as an individual mineral clast and is unzoned or has sector and or oscillatory zoning the age of primary zircon is obtained when multiple ion microprobe analyses across the polished surface of the grain give reproducible and essentially concordant data a secondary set of microstructures superimposed on primary zircon include localised recrystallised domains localised amorphous domains crystal plastic deformation planar deformation features and fractures and are associated with impact processes the first two secondary microstructures often yield internally consistent and close to concordant u pb ages that we interpret as dating impact events others secondary microstructures such as planar deformation features crystal plastic deformation and micro fractures can provide channels for pb diffusion and result in partial resetting of the u pb isotopic systems

fluxes of 226ra and barium in the pacific ocean the importance of boundary processes abstract the 226 ra ba ratio in particles collected in sediment traps decreases with depth fluxes of ba and al increase with depth these observations cannot be explained by simple vertical processes instead they require a component to the deep flux which originates at the ocean margins we suggest that the deep traps are enriched in ba through the advection of barite originally precipitated in biologically productive regions of the ocean margin this source is less important for 226 ra because some is lost by radioactive decay between the precipitation of barite on the margin and outward transport the boundary flux is an important source of material to the deep sea from 226 ra fluxes in the upper 1000 m of the water column we estimate that the residence time of 226 ra in the upper ocean is 400 years the removal of 226 ra in the particle flux is approximately balanced by the upwelling of waters enriched in 226 ra

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

organic geochemistry of impactites from the haughton impact structure devon island nunavut canada organic matter in impactites from the 24 km wide and 39 ma old haughton impact structure canadian high arctic is a mixture of fossil and modern biological components the fossil component represents a conventional oil that was generated from lower palaeozoic marine source material before impact and permeates bedrock dolomites biomarker maturity parameters record the thermal effect of the mid tertiary impact maturity influenced sterane rearranged hopanoid and triaromatic steroid ratios all increase towards the centre of the impact structure where thermal alteration was greatest the heating was probably dominated by an impact related hydrothermal system as such systems last long enough for kinetically based thermal alteration to occur kinetically related biomarker data suggest that the hydrothermal heating lasted for c 5000 years biomarkers are also preserved in dolomite clasts within impact melt breccia and indicate strong thermal alteration modern biological contamination of the rocks is responsible for the superposition of two geochemical signatures which could be cyanobacteria non marine algae or higher plant matter onto the fossil component but they can be recognized and distinguished the data show that the impact structure system holds a record of both the pre impact organic signature and the thermal signature of the impact and thereby indicates that organic geochemistry is a valuable tool in documenting the response of rocks to impacts

228ra as a tracer for shelf water in the arctic ocean during its formation on the vast siberian shelves arctic surface water is strongly enriched in 228ra when 228ra of surface samples from the arctic interior is plotted against the river water component fr derived from salinity 180 and silicate as tracers a shelfwater end member can be calculated by extrapolation highest values occur in the core of the transpolar drift indicating rapid transport of surface water comparable to the known ice drift pattern low values at ice island t3 are explained by radioactive decay 5 8 year half life during the long residence time of fresh and shelf influenced water in the beaufort gyre some evidence of decay and consequently prolonged transit times is also observed in the southern nansen basin future research is required to establish the seasonal interannual and spatial variability of 228ra on the shelves in order to determine the full potential of 228ra as a tracer for the origin and transport rates of shelfwater in the arctic basin apart from the usual 228ra signature of bottom waters the tracer is also observed in intermediate layers where it gives evidence of recent contact with slope or shelf sediments the atlantic inflow along the barents slope is enriched down to 2000 m the return flow over the amundsen basin and lomonosov ridge carries a shelf signature of 228ra and 228th down to more than 1200 m depth in agreement with the enrichment observed in 137cs deeper maxima around 1900 2500 m in the nansen basin are interpreted as inflow of bottom water from the norwegian sea through fram strait

the interior shelves of the arctic ocean physical oceanographic setting climatology and effects of sea ice retreat on cross shelf exchange abstract the interior shelves of the arctic mediterranean are the shelves of the kara sea laptev sea east siberian sea and beaufort sea they comprise approximately 40 of the total arctic shelf area 2 5 10 6 km 2 and are distinguished from inflow and outflow shelves by their principal forcing dynamics along their southern continental boundary the interior shelves are dominated by the major arctic rivers receiving over 80 of the total freshwater input to the arctic ocean in the mid shelf region wind and ice motion surface stresses dominate mixing and circulation resulting in high variability along their northern seaward boundary they are forced by upwelling and downwelling favourable surface stresses which drive shelf basin exchanges with atlantic and pacific origin cyclonic boundary currents over the upper slope shelf basin exchange is further modified by shelf break morphometry e g canyons valleys headlands and bottom slope here we review the physical oceanographic settings and forcing of the interior shelves and then focus on shelfbreak exchange and supply of nutrients for new primary production due to upwelling across the shelfbreak as a proxy for this nutrient supply we show seasonal and annual time series of along shelfbreak surface stress due to wind and ice motion from 1979 to 2011 we apply this analysis to the shallow shelves from the kara sea to the beaufort sea and comment on recent increases due to atmospheric changes and sea ice retreat

divergent patterns of recent sea ice cover across the bering chukchi and beaufort seas of the pacific arctic region abstract over the past three decades of the observed satellite record there have been significant changes in sea ice cover across the bering chukchi and beaufort seas of the pacific arctic region par satellite data reveal that patterns in sea ice cover have been spatially heterogeneous with significant declines in the chukchi and beaufort seas yet more complex multi year variability in the bering sea south of st lawrence island these patterns in the chukchi and beaufort seas have intensified since 2000 indicating a regime shift in sea ice cover across the northern portion of the par in particular satellite data over 1979 2012 reveal localized decreases in sea ice presence of up to 1 64 days year canada basin and 1 24 days year beaufort sea which accelerated to up to 6 57 days year canada basin and 12 84 days year beaufort sea over the 2000 2012 time period in contrast sea ice in the bering sea shows more complex multi year variability with localized increases in sea ice presence of up to 8 41 days year since 2000 the observed increases in sea ice cover since 2000 in the southern bering sea shelf region are observed in wintertime whereas sea ice losses in the canada basin and beaufort sea have occurred during summer we further compare sea ice variability across the region with the national centers for environmental prediction ncep north american regional reanalysis narr wind and air temperature fields to determine the extent to which this recent variability is driven by thermal vs wind driven processes results suggest that for these localized areas that are experiencing the most rapid shifts in sea ice cover those in the beaufort sea are primarily wind driven those offshore in the canada basin are primarily thermally driven and those in the bering sea are influenced by elements of both sea ice variability and its drivers across the par provides critical insight into the forcing effects of recent shifts in climate and its likely ultimate profound impacts on ecosystem productivity across all trophic levels

hypsometry and volume of the arctic ocean and its constituent seas 1 this paper presents an analysis of the arctic ocean and its constituent seas for seafloor area distribution versus depth and ocean volume the bathymetry from the international bathymetric chart of the arctic ocean ibcao is used together with limits defining this ocean and its constituent seas from the international hydrographic organization iho as well as redefined limits constructed to confine the seas to the shallow shelves ibcao is a bathymetric grid model with a resolution of 2 5 2 5 km which significantly improved the portrayal of the arctic ocean seafloor through incorporation of newly released bathymetric data including echo soundings from u s and british navies scientific nuclear submarine cruises and icebreaker cruises this analysis of seafloor area and ocean volume is the first for the arctic ocean based on this new and improved portrayal of the seafloor as represented by ibcao the seafloor area and volume are calculated for different depths starting from the present sea level and progressing in increments of 10 m to a depth of 500 m and in increments of 50 m from 550 m down to the deepest depth within each of the analyzed seas hypsometric curves expressed as simple histograms of the frequencies in different depth bins and depth plotted against cumulative area for each of the analyzed seas are presented the area and volume calculations show that the entire iho defined arctic ocean makes up 4 3 of the total ocean area but only 1 4 of the volume furthermore the iho arctic ocean is the shallowest mean depth 1201 m of all the major oceans and their adjacent seas the continental shelf area from the coasts out to the shelf break make up as much as 52 9 of the total area in the arctic ocean defined in this work as consisting of the oceanic deep arctic ocean basin the broad continental shelves of the barents kara laptev east siberian chukchi and beaufort seas the white sea and the narrow continental shelf off both the canadian arctic archipelago and northern greenland this result indicates that the arctic ocean has significantly larger continental shelves compared with all the other oceans where previous studies show that the proportion of shelves from the coasts out to the foot of the continental slopes only ranges between about 9 1 and 17 7 furthermore the derived hypsometric curves show that most of the arctic ocean shelf seas besides the barents sea beaufort sea and the shelf off northern greenland have a similar shape with the largest seafloor area between 0 and 50 m the east siberian and laptev seas in particular show area distributions concentrated in this shallow depth range and together with the chukchi sea they form a large flat shallow shelf province composing as much as 22 of the entire arctic ocean area but only 1 of the volume this implies that the circulation in the arctic ocean might be very sensitive to eustatic sea level changes one of the aims with this work is to make up to date high resolution area and volume calculations for the arctic ocean at various depths available for download

228ra 226ra and 226ra ba ratios to track barite formation and transport in the water column abstract we measured 228 ra ex 226 ra ex and 226 ra ex ba ex ratios in suspended and sinking particles collected at the oceanic flux program ofp time series site in the western sargasso sea and compared them to seawater ratios to provide information on the origin and transport of barite baso 4 in the water column the 228 ra ex 226 ra ex ratios of the suspended particles down to 2000 m are nearly identical to those of seawater at the same water depth these ratios are much lower than expected if suspended barite was produced in surface waters and indicate that barite is produced throughout the mesopelagic layer the 228 ra ex 226 ra ex activity ratios of sinking particles collected at 1500 and 3200 m varied mostly between 0 1 and 0 2 which is intermediate between the seawater ratio at these depths ex ba total ba lithogenic considered to be mainly barite present in the sinking flux is a mixture of crystals formed recently in the upper water column formed several years earlier in the upper water column or formed recently in deeper waters we observe a sizeable temporal variability in the 228 ra ex 226 ra ex ratios of sinking particles which indicates temporal variability in the relative proportion of barite crystals originating from surface with a high 228 ra ex 226 ra ex ratio and mesopelagic with a low 228 ra ex 226 ra ex ratio sources however we could not discern a clear pattern that would elucidate the factors that control this variability the 226 ra ba ratios measured in seawater are consistent with the value reported from the geosecs expeditions 2 3 dpm mol 1 below 500 m depth but are significantly lower in the upper 500 m high 226 ra ex ba ex ratios and elevated sr concentrations in suspended particles from the upper water column suggest preferential uptake of 226 ra over ba during formation of srso 4 skeletons by acantharians which must contribute to barite formation in shallow waters deeper in the water column the 226 ra ex ba ex ratios of suspended particles are lower than those of seawater since 228 ra ex 226 ra ex ratios demonstrate that suspended barite at these depths has been produced recently and in situ their low 226 ra ex ba ex ratios indicate preferential uptake of ba over ra in barite formed in mesopelagic water

circulation dense water formation and outflow on the northeast chukchi shelf we investigated circulation and water mass modification processes in the chukchi sea using 1 temperature salinity and velocity data collected between september 1991 and september 1992 from moorings in bering strait and the northeast shelf and 2 meteorological data and ice concentrations derived from special sensor microwave imager ssm i imagery in october 1991 and from february to august 1992 the mean monthly circulation was steady and northward from november to january strong northeast winds diverted the low salinity bering inflow onto the western shelf and weakened and reversed flow over the northeast shelf the winds also opened extensive polynyas wherein cold hypersaline salinity 34 waters formed the fall winter circulation enhanced dense water formation by diverting low salinity waters away from and prolonging the residence time of water within the polynyas alongshore convergence of the coastal flow swept some of the cold hypersaline water offshore across isobaths but the coastal current carried most of it into the arctic ocean through barrow canyon the dense outflow mixed little during its descent through the upper canyon where bottom friction and rotation but not entrainment were important in the plume momentum balance if the outflow is not diluted by mixing in the lower canyon where theory suggests this will occur then the densest shelf waters can ventilate layers deeper than the halocline salt rejection estimates using ssm i data and surface heat budget calculations agree within a factor of 2 with independent estimates from the mooring hence remote sensing techniques can monitor winter salt rejection rates in the chukchi sea

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

submarine groundwater discharge revealed by 228 ra distribution in the upper atlantic ocean submarine groundwater discharge estimated from a 228ra inventory across the upper atlantic ocean provides a flux of 2 4 1013 m3 yr 1 equivalent to 80 160 of the influx from rivers into the atlantic ocean