plutonium in the western north pacific transport along the kuroshio and implication for the impact of fukushima daiichi nuclear power plant accident abstract this study examined pu source terms in the western north pacific wnp based on data collected in 2014 and 2015 the basin wide 240pu 239pu atom ratios ranged from 0 227 to 0 263 with an average value of 0 244 0 011 consistently higher than that of global fallout 0 180 the spatial distribution of 240pu 239pu atom ratios showed higher values within the kuroshio region the main western ocean boundary current as compared to the zone off of the kuroshio there was also an overall decreasing trend of 240pu 239pu along the kuroshio path to its extensions 239 240pu activities in surface seawater exhibited a wide range from 1 15 to 4 30 mbq m 3 and their spatial distribution showed an increasing trend with latitude unlike the 240pu 239pu atom ratios which had heavier isotopic compositions in the kuroshio mainstream compared to the zone off of the kuroshio the 239 240pu activities were higher outside the kuroshio than within the kuroshio these patterns in both pu isotopic ratios and activities point towards a unique close in fallout source which levels down in its source term and has a high degree of scavenging during its transport along the kuroshio and can be traced back to a precursor the north equatorial current which originates near the pacific proving grounds ppg with characteristically higher 240pu 239pu atom ratios high 240pu 239pu atom ratios found in the zone outside the kuroshio were transported from the kuroshio via the formation and circulation of north pacific intermediate water we further revealed using a simple two end member mixing model that the ppg source contributed 60 13 of the pu in the kuroshio zone and 45 10 in the zone off of the kuroshio both the comparison of pu isotopic composition in the wnp within a radius of 500 km or 1000 km off the fukushima daiichi nuclear power plant fdnpp between prior to and post the accident and a simple first order mass balance calculation in terms of atmospheric deposition and release suggest that the pu originating from the fdnpp accident if any was either negligible or the input flux of 239 240pu was too small to significantly alter the pu isotopic composition in the ambient seawater this article is part of a special issue entitled cycles of trace elements and isotopes in the ocean geotraces and beyond edited by tim m conway tristan horner yves plancherel and aridane g gonzalez

plutonium 241am and 137cs ratios inventories and vertical profiles in washington and oregon continental shelf sediments abstract continental shelf sediments from nine locations off washington and oregon have 239 240 pu inventories which average 8 0 2 6 mci km 2 the columbia river and seawaters advecting over the shelf supply pu which is removed to underlying sediments principally through scavenging by inorganic paniculate matter mass balance calculations argue that less than 20 percent of the advected pu need be scavenged from the water column to balance river input and total shelf sediment inventories the percentage of the pu removed through scavenging is consistent with observed participate concentrations in shelf waters and published sediment water distribution coefficients no marked separation of pu from 137 cs is observed with depth in pacific shelf sediments as has been reported in atlantic coastal sediments this interocean distinctness can be explained by differences in particle mixing and downward diffusion of cs in sediments of varying porosities the transuranic inventories and pu cs ratios in the pacific sediments do not support the hypothesis of livingston and bowen that pu is remobilized within the sediment column by complexone formation with principally organic substances excess 210 pb 239 240 pu inventory ratios in eight representative cores from the washington shelf average 100 19 even though absolute values of both inventories vary by much larger factors this reasonably constant ratio for a given water depth permits estimation of total pu inventories and prediction of sites of unusual pu accumulation from data on the more easily measured natural radionuclide

transport and deposition of plutonium in the ocean evidence from gulf of mexico sediments abstract a study of sediments in the gulf of mexico shows dramatic gradients in pu content and isotope ratios from the continental shelf to the sigsbee abyssal plain in terms of predicted direct fallout inventory of pu one shelf core contains 745 of the predicted inventory while abyssal plain sediments contain only 15 20 of the predicted value absolute pu concentrations of shelf sediments are also conspicuously high up to 110 dpm kg compared to 13 5 dpm kg in mississippi river suspended sediment there is no evidence of pu remobilization in gulf of mexico shelf sediments based on comparison of pu profiles with mn al and fe al profiles horizontal transport of fallout nuclides from the open ocean to removal sites in ocean margin sediments is concluded to be the source of both the high concentrations and high inventories of pu reported here the shelf sediments show 240 pu 239 pu ratios close to 0 179 the average stratospheric fallout value but the ratios decrease progressively across the gulf to low values of 0 06 in abyssal plain sediments the source of low ratio pu in deep water sediments may be debris from low yield tests transported in the troposphere alternatively it may represent a fraction of the pu from global stratospheric fallout which has been separated in the water column from the remainder of the pu in the ocean in either case the low ratio material must have been removed rapidly to the sea floor where it composes a major fraction of the pu in abyssal plain sediments pu delivered by global atmospheric fallout from the stratosphere has apparently remained for the most part in the water or has been transported horizontally and removed into shallow water sediments

denitrification rates and availability of organic matter in marine environments abstract relationships between denitrification rates and availability of organic matter in three types of marine environments water column water sediment interface and sediments were delineated correlation between supply and demand of organic matter for denitrification in the first two types of environments suggests that denitrification is mainly supported by organic matter provided as macroparticles from the euphotic zone decomposition of organic matter during denitrification in the water column of certain high productivity areas is at a minimum 1 4 to 1 2 as effective as the respiratory processes which use dissolved oxygen fifty percent or more of organic macroparticles deposited on the sea floor can be consumed by denitrification at the sediment water interface in hemipelagic sediments the first order denitrification rate constant which appears to be sensitively dependent on organic carbon content can be roughly expressed as k d 0 60c 2 1 where k d is rate constant in yr 1 and c is the percentage of organic carbon the total turnover of nitrogen by denitrification is here estimated to be 42 69 tg n yr 1 for the global oceans which can be divided into three separate categories 27 44 tg n yr 1 in the oxygen deficient water column 3 13 tg n yr 1 for the water sediment interface and approximately 12 tg n yr 1 for the sediment column

role of large particles in the transport of elements and organic compounds through the oceanic water column abstract during the past decade data from a variety of sources have been obtained which show conclusively that the relatively rare large particles sinking through the water column are responsible for the majority of the downward vertical mass flux in the sea this finding has important implications for understanding the transfer distribution and fate of elements and organic compounds in marine waters the large 100 m detrital particles responsible for vertical flux are primarily biogenic and range in size and composition from small discrete fecal pellets and plankton hard parts to large amorphous aggregates or snow which contain both organic and inorganic constituents depending on size shape and density these particles sink at rates ranging from 1000 m day 1 several methods have been developed for sampling these particles of which in situ sediment trapping has probably furnished the most comprehensive qualitative and quantitative information on the role large particles play in material transport flux studies have highlighted the importance of marine heterotrophs in packaging fine suspended particulate matter into large rapidly sinking particles which accelerate the movement of incorporated materials to depth large particle production via biological packaging is not restricted to the euphotic zone but can occur at all depths and information is now accruing on rates of production of large particles in the water column chemical analyses of sedimenting particles collected in sediment traps and those sampled by other means have allowed quantifying vertical fluxes and residence times of elements radionuclides and organic compounds natural and anthropogenic in various oceanic regimes pertinent studies dealing with the above aspects are reviewed and several areas for future research are suggested

a depth profile of uranium 236 in the atlantic ocean abstract in this study the first two oceanic depth profiles of 236u sampled in the western equatorial atlantic ocean are presented the measured 236u 238u ratios decrease from about 10 9 at the surface down to about 10 10 even the lowest ratios measured below 4000 m depth are more than three orders of magnitude above the estimated natural 236u 238u level for the pre anthropogenic ocean this clearly indicates that anthropogenic 236u already has reached the deep atlantic ocean three different conceptual models are applied to identify the relevant processes capable of transporting significant amounts of 236u from the surface into the deep ocean while the vertical transport of particulate u is excluded as a significant source box model calculations suggest that north atlantic deep water production with some minor contribution of 236u from nuclear reprocessing as the most likely source for 236u in the deep western equatorial atlantic ocean our results show that 236u has a large potential as a new conservative and transient tracer in oceanography

plutonium and210pb distributions in northeast atlantic sediments subsurface anomalies caused by non local mixing abstract the depth distributions of 210 pb and 239 240 pu measured in a suite of box cores collected from water depths of 4000 5000 m in the northeast atlantic ocean exhibit pronounced subsurface maxima caused by sediment reworking by benthic infauna small scale spatial heterogeneity in bioturbation rates is indicated by large differences in tracer profiles from duplicate cores separated only by a few centimeters 210 pb and 239 240 pu activity distributions from each subcore exhibit a high degree of correlation and most tracer profiles exhibit one or more subsurface maxima one dimensional biodiffusion analogue models do not adequately simulate the principal features of this data set however an inverse conveyer belt mixing model which simulates subsurface egestion or a functionally equivalent process of surficial material which is enriched both in organic debris and radioactive tracers can reproduce the subsurface tracer maxima single event and continuous subsurface egestion models have been formulated and solved for different feeding rates and background biodiffusive fields the single event model provides a better fit to the data and in particular ensures the observed high degree of correlation between the 210 pb and 239 240 pu activity profiles regardless of the different tracer input functions the most likely candidate responsible for subsurface tracer egestion is a large infaunal worm of the phylum sipunculida which dominates the biomass below a depth of 3 cm

two stages of granulite facies metamorphism in the eastern himalayan syntaxis south tibet petrology zircon geochronology and implications for the subduction of neo tethys and the indian continent beneath asia the eastern himalayan syntaxis in southeastern tibet consists of the lhasa terrane high himalayan rocks and indus tsangpo suture zone the lhasa terrane constitutes the hangingwall of a subduction zone whereas the high himalayan rocks represent the subducted indian continent our petrological and geochronological data reveal that the lhasa terrane has undergone two stages of medium p metamorphism an early granulite facies event at c 90 ma and a late amphibolite facies event at 36 33 ma however the high himalayan rocks experienced only a single high p granulite facies metamorphic event at 37 32 ma it is inferred that the late cretaceous c 90 ma medium p metamorphism of the southern lhasa terrane resulted from a northward subduction of the neo tethyan ocean and that the oligocene 37 32 ma high p 1 8 1 4 gpa rocks of the high himalayan and coeval medium p 0 8 1 1 gpa rocks of the lhasa terrane represent paired metamorphic belts that resulted from the northward subduction of the indian continent beneath asia our results provide robust constraints on the mesozoic and cenozoic tectonic evolution of south tibet

particle mixing rates in sediments of the eastern equatorial pacific evidence from 210pb 239 240pu and 137cs distributions at manop sites abstract particle mixing rates db calculated from excess 210pb gradients in sediments of the east equatorial pacific range from 0 04 to 0 5 cm2 y with variation of a factor of 3 4 at a single site diffusion of the 236ra daughter 222rn may affect 210pb distributions under conditions of slow mixing and low 210pb flux to the seafloor as shown by a siliceous ooze clay core which contained the fallout radionuclides 239 240pu and 137cs but no excess 210pb relative to 226ra there is no clear relationship between 210pbderived mixing rates and sediment type accumulation rate or organic carbon flux to the sediments comparison of 210pb mixing rates with those calculated from 239 240pu and 137cs distributions reveals better agreement for a pulse input of the fallout radionuclides db 0 03 0 4 cm2 y than for continuous input at a constant rate db 0 1 1 6 cm2 y although the pu and 137cs data are better fit by the latter model the agreement may be fortuitous because 239 240pu and 137cs appear significantly deeper than 210pb in at least one core tracer separation could be caused by particle size selective mixing by the benthic fauna or by chemical mobilization if the fallout radionuclides are scavenged from surface waters by large organic rich particles such as fecal pellets their release and migration may result from decomposition of the carrier in surface sediments either a relatively unreactive form of pu e g oxidized pu has been released by this process or a one dimensional model is inadequate to explain its observed penetration into the sediments activity ratios of 239 240 pu 137 cs in the sediments decrease with increasing north latitude and the trend reflects higher fluxes of 239 240pu near the weapons test site at christmas island 2 n the 239 240 pu 137 cs ratios and fluxes to the sediment assuming constant input at the siliceous ooze red clay site are consistent with published sediment trap data from a nearby site thus if fallout radionuclide fluxes to the sea floor were higher in the past both 239 240pu and 137cs have been released from sinking particles

the south tibetan detachment system facilitates ultra rapid cooling of granulite facies rocks in sikkim himalaya 1 the eastern himalaya is characterized by a region of granulites and local granulitized eclogites that have been exhumed via isothermal decompression from lower crustal depths during the india asia collision spatially most of these regions are proximal to the south tibetan detachment system an orogen parallel normal sense detachment system that operated during the miocene suggesting that it played a role in their exhumation here we use geo and thermochronological methods to study the deformation and cooling history of footwall rocks of the south tibetan detachment system in northern sikkim india these data demonstrate that the south tibetan detachment system was active in sikkim between 23 6 and 13 ma and that footwall rocks cooled rapidly from 700 to 120 c between 15 13 ma while active the south tibetan detachment system exhumed rocks from mid crustal depths but an additional heat source such as strain heating advected melt and or crustal thinning is required to explain the observed isothermal decompression cessation of movement on the south tibetan detachment system produced rapid cooling of the footwall as isotherms relaxed a regional comparison of temperature time data for the eastern south tibetan detachment system indicates a lack of synchronicity between the sa er sikkim yadong section and the nw bhutan section to accommodate this requires either strike slip tear faulting or local out of sequence thrusting in the younger segment of the orogen

sedimentation and mixing rates of radionuclides in barents sea sediments off novaya zemlya abstract radionuclide measurements have been conducted on sediment cores collected in 1992 in the south eastern region of the barents sea known as the pechora sea cesium 137 and 239 24opu activities in surface sediments are generally less than 30 bq kg with the highest levels being measured in sediments off the southwestern coastline of the island of novaya zemlya high correlations between both 137cs and 239 24opu and the concentration of fine the 238 pu 239 240 vu activity ratio of 0 0245 in chernaya bay is equivalent to values measured in global fallout the 240 pu 239 pu atom ratio 0 0304 measured by mass spectrometry is much lower than values 0 18 typical of global fallout but is consistent with ratios measured for fallout from the early 1951 1955 series of weapons tests at the nevada test site the timing of the chernaya bay source term estimated from the 241 am 241 pu ratio is consistent with the timing of the 1955 and 1957 underwater nuclear tests relatively low initial yields of 241pu 241 pu 239 pu atom ratio 0 00 123 in these tests have resulted in relatively low 241 am 239 240 pu activity ratios 0 05 in recent sediments in chernaya bay radionuclide tracer profiles in cores from the pechora sea can be simulated using a two layer biodiffusion model with rapid near homogeneous mixing in the surface mixed layer and reduced mixing in the deep layer lead 210 profiles are consistent with a wide range of sedimentation and mixing rates in the deep sediment layer however the 137cs and 239 240pu results further constrain the model parameters and indicate that the downward transport of radionuclides in the sediments is governed primarily by sediment mixing with sediment burial playing a secondary role

the geochemistry of fallout plutonium in the north atlantic ii ratios and their significance a systematic decrease in the 240pu239pu ratio in marine sediments is found with increasing water depth along a transect of cores between woods hole and bermuda the 240pu239pu atom ratios range from o 18 on the shelf to o 10 at 5000 m but do not change with depth in individual cores a model is presented which can account for the range of 240pu239pu ratios found in this and other similar studies noshkin and gatrousis 1974 scottet al 1983 we propose that there have been at least two distinct sources of fallout pu to this region the major source of pu is global stratospheric fallout characterized by a 240pu239pu ratio of 0 18 and a relatively long residence time in seawater the second source is characterized by a much lower 240pu239pu ratio and relative to global fallout it must have been much more efficiently removed from the water column to deep sea sediments we suggest that surface based low yield testing at the nevada test site is the only source of low ratio fallout pu which could account for the timing inventories and refractory characteristics of this second component of fallout pu inputs to the north atlantic

determination of mixing parameters from tracer distributions in deep sea sediment cores abstract computer optimization and approximate analytical procedures are developed for the determination of the depth of bioturbation mixing d and the mixing coefficient d for instantaneous tracer inputs the methods have been applied to observations of microtektites volcanic ash and pumice in sixteen deep sea sediment cores the values for d are well determined generally with confidence intervals of a few centimeters or less and with an average value of d 11 cm for the sixteen cores the values for d are determined to first figure accuracy at best with values of around 10 cm 2 ka 1 or greater

the geochemistry of fallout plutonium in the north atlantic i a pore water study in shelf slope and deep sea sediments abstract the distribution of fallout plutonium between pore waters and sediments in the northwest atlantic is examined in order better to define the potential for pu migration from and within marine sediments along a transect of seven cores collected between woods hole and bermuda the solid phase 239 240pu 210pbex and 137cs results do not suggest that any of these tracers are preferentially mobile within the cores pore water pu activities appear to be controlled primarily by the distribution of pu in the solid phase with an operationally determined distribution coefficient kd in the range of 0 2 23 104 there is a trend in the kds along the transect with higher values in the 104 105 range on the shelf and slope to lower values 239 240 pu cm 2 year sediment mixing models are not significantly altered by the inclusion of pu diffusion terms since the pore water terms are so small relative to typical sediment mixing rates

pu 137cs and excess 210pb in russian arctic sediments the activity ratios of pu and radiocesium isotopes have been used to delineate the major sources such as global and close in debris fallout nuclear fuel reprocessing and fabrication plant effluents in the environment we have measured 238pu 239 240pu 137cs and excess 210pb concentrations in 107 surficial sediments as well as in 5 sediment cores collected in the summer months of 1993 and 1994 from the ob and yenisey rivers russia and the kara sea a comparison of the sediment core inventories of 239 240pu and 137cs along with the 238pu 239 240pu activity ratios with those expected from global fallout allows us to estimate the relative amounts if any of reactor derived 238pu and 239 240pu from the dumped reactor sites in the study area in surficial sediment samples collected in 1993 and 1994 the 239 240pu concentrations varied between 4 2 and 856 mbq kg 1 with a mean of 239 mbq kg 1 in samples with a measurable 238pu the 238pu 239 240pu activity ratios varied between 0 010 and 0 069 with an average value of 0 035 0 014 this range can be compared to the average 238pu 239 240pu activity ratio of 0 030 for the year 1993 from nuclear weapons testing and snap fallout obtained from soil studies indicating very little 5 additional sources of 238pu to the sediments in the study area the inventories of pu in the 5 sediment cores from the study area varied between 2 67 0 67 and 24 5 2 2 bq m 2 with a mean value of 8 83 bq m 2 the 137cs concentrations in the upper 3 cm of the sediments varied between below detection limit to 71 4 bq kg 1 with a mean of 14 9 bq kg 1 the 137cs inventories in the 5 sediment cores varied between 156 7 28 3 and 1600 153 3 bq m 2 with a mean value of 583 3 bq m 2 the mean ratio of inventories of pu to that of 137cs 0 015 is comparable to the values in other places in the arctic region there is a significant correlation between total organic carbon and concentrations of 137cs 239 240pu and 210pb suggesting that organic matter enriched fine particles are a likely carrier phase for these nuclides the ratio of 137cs 239 240pu also suggests that most of these nuclides are derived from global fallout

plutonium activities and 240pu 239pu atom ratios in sediment cores from the east china sea and okinawa trough sources and inventories abstract plutonium concentrations and 240 pu 239 pu atom ratios in the east china sea and okinawa trough sediment cores were determined by isotope dilution inductively coupled plasma mass spectrometry after separation using ion exchange chromatography the results showed that 240 pu 239 pu atom ratios in the east china sea and okinawa trough sediments ranging from 0 21 to 0 33 were much higher than the reported value of global fallout 0 18 the highest 240 pu 239 pu ratios 0 32 0 33 were observed in the deepest okinawa trough sediment samples these ratios suggested the us nuclear weapons tests in the early 1950s at the pacific proving grounds in the marshall islands were a major source of plutonium in the east china sea and okinawa trough sediments in addition to the global fallout source it was proposed that close in fallout plutonium was delivered from the pacific proving grounds test sites via early direct tropospheric fallout and transportation by the north pacific equatorial circulation system and kuroshio current into the okinawa trough and east china sea the total 239 240 pu inventories in the cores were about 150 200 of that expected from direct global fallout about 46 67 of the total inventories were delivered from the pacific proving grounds much higher 239 240 pu inventories were observed in the east china sea sediments than in sediments of the okinawa trough because in the open oceans part of the 239 240 pu was still retained in the water column and continued pu scavenging was higher over the margin than the trough according to the vertical distributions of 239 240 pu activities and 240 pu 239 pu atom ratios in these cores it was concluded that sediment mixing was the dominant process in controlling profiles of plutonium in this area faster mixing in the coastal samples has homogenized the entire 240 pu 239 pu ratio record today slightly slower mixing and less scavenging in the okinawa trough have left the surface sediment ratios closer to the modern north pacific water end member and higher ratios 0 30 0 34 at the bottom of the cores

exhumation of the ultrahigh pressure tso morari unit in eastern ladakh nw himalaya a case study exhumation processes of the ultra high pressure uhp tso morari dome nw himalaya are investigated using structural petrological and geochronological data the uhp tso morari unit is bounded by the low grade metamorphic indus suture zone to the ne and mata unit to the sw three deformation phases d1 d2 and d3 are observed only d3 is common to the uhp unit and the surrounding units in the uhp unit the first deformation phase d1 produced upright folds under eclogitic conditions 20 kbar 580 60 c d1 is overprinted by d2 structures related to a nw se trending open anticline this phase is characterized by blueschist mineral associations and corresponds to the quasi isothermal decompression from a depth of 90 km eclogitic conditions up to 30 40 km the final exhumation phase of the tso morari unit is dominated by tectonic denudation and erosion d3 associated with a slight temperature increase radiochronological analyses indicate that the uhp exhumation process began during the eocene exhumation was fast during d1 d2 and slowed down through d3 in oligocene time the change in the deformation style from d1 d2 to d3 in the tso morari unit coincides with changes in the exhumation rates and in the metamorphic conditions these changes may reflect the transition from an exhumation along the subduction plane in a serpentinized wedge to the vertical uplift of the tso morari unit across the upper crust

assembly of the lhasa and qiangtang terranes in central tibet by divergent double subduction abstract integration of lithostratigraphic magmatic and metamorphic data from the lhasa qiangtang collision zone in central tibet including the bangong suture zone and adjacent regions of the lhasa and qiangtang terranes indicates assembly through divergent double sided subduction this collision zone is characterized by the absence of early cretaceous high grade metamorphic rocks and the presence of extensive magmatism with enhanced mantle contributions at ca 120 110 ma two jurassic cretaceous magmatic arcs are identified from the caima duobuza rongma kangqiong amdo magmatic belt in the western qiangtang terrane and from the along tso yanhu daguo baingoin daru tso magmatic belt in the northern lhasa terrane these two magmatic arcs reflect northward and southward subduction of the bangong ocean lithosphere respectively available multidisciplinary data reconcile that the bangong ocean may have closed during the late jurassic early cretaceous most likely ca 140 130 ma through arc arc soft collision rather than continent continent hard collision subduction zone retreat associated with convergence beneath the lhasa terrane may have driven its rifting and separation from the northern margin of gondwana leading to its accretion within asia

distribution and inventories of 90sr 137cs 241am and pu isotopes in sediments of the northwest pacific ocean abstract bottom sediments collected in the northwest nw pacific ocean in 1997 were analysed for 90 sr 137 cs 239 240 pu and 241 am contents to determine their distribution patterns inventories and sources enhanced inventories of 239 240 pu and 241 am were observed in the latitudinal belts of 10 20 n and 30 40 n which correspond to major areas of local tropospheric and global stratospheric fallout with a contribution from local fallout respectively the sediment inventory of 239 240 pu near the bikini atoll exceeded its overlying water inventory however in the mid latitudes more than 70 of 239 240 pu still remains in the water column 241 am inventories in sediments exceeded that of the water column for the entire nw pacific ocean higher 137 cs and 90 sr sediment inventories in the latitudinal belt of 30 40 n are due to global fallout and they account for about 10 and less than 5 of the water column inventories respectively the observed activity ratios of 137 cs 90 sr 238 pu 239 240 pu and 241 am 239 240 pu in sediment were at some stations higher than the global fallout ratios due to contributions from local fallout and due to specific processes in the water column two end member mixing model based on the 240 pu 239 pu atom ratios observed in global and local fallout yielded 60 contribution of the local fallout in the bottom sediments near the bikini atoll the upward decrease in the 240 pu 239 pu atom ratios in the sediment column indicates a decrease in the contribution of local fallout to the pu inventory with time 241 am and 241 pu dating of sediment layers was utilized to explain a hiatus in sediment accumulation in the deep seafloor

particle mixing rates in deep sea sediments determined from excess 210pb and 32si profiles particle mixing rates have been determined for 5 south atlantic antarctic and 3 equatorial pacific deep sea cores using excess 210 pb and 32 si measurements radionuclide profiles from these siliceous calcareous and clay rich sediments have been evaluated using a steady state vertical advection diffusion model in antarctic siliceous sediments 210 pb mixing coefficients 0 04 0 16 cm 2 y are in reasonable agreement with the 32 si mixing coefficient 0 2 or 0 4 cm 2 y depending on 32 si half life in an equatorial pacific sediment core however the 210 pb mixing coefficient 0 22 cm 2 y is 3 7 times greater than the 32 si mixing coefficient 0 03 or 0 07 cm 2 y the difference in 210 pb and 32 si mixing rates in the pacific sediments results from 1 non steady state mixing and differences in characteristic time and depth scales of the two radionuclides 2 preferential mixing of fine grained clay particles containing most of the 210 pb activity relative to coarser particles large radiolaria containing the 32 si activity or 3 the supply of 222 rn from the bottom of manganese nodules which increases the measured excess 210 pb activity relative to 226 ra at depth and artificially increases the 210 pb mixing coefficient based on 32 si data and pore water silica profiles dissolution of biogenic silica in the sediment column appears to have a minor effect on the 32 si profile in the mixed layer deep sea particle mixing rates reported in this study and the literature do not correlate with sediment type sediment accumulation rate or surface productivity based on differences in mixing rate among three antarctic cores collected within 50 km of each other local variability in the intensity of deep sea mixing appears to be as important as regional differences in sediment properties

growth rate of a deep sea coral using 210pb and other isotopes abstract a deep sea coral was studied to determine its growth rate and to reconstruct time histories of isotope distributions in the deep ocean the specimen was collected at a depth of 600 m off little bahama banks using the deep submergence vehicle dsv alvin the growth rate of the calcitic coral trunk was determined using excess 210pb measured in concentric bands excess 210pb was found in the outer half of the coral s radius and a growth rate of 0 11 0 02 mm a is calculated assuming a constant growth rate during formation of the entire trunk an age of 180 40 a is estimated for the coral the decrease observed in radiocarbon activities measured on the same bands griffin and druffel 1989 concurred with the growth rate estimated from excess 210pb activity 239 240pu activities measured by mass spectrometry were also detected in the outer two bands of the coral as expected from the 210pb chronology stable oxygen and carbon isotopes measured in samples collected by a variety of techniques are positively correlated this is evidence of a variable kinetic isotope effect most likely caused by variations in the skeletal growth rate long lived corals such as this specimen have the potential for serving as integrators of seawater chemistry in the deep sea over several century timescales

variability of natural and bomb produced radionuclide distributions in abyssal red clay sediments the nature of sedimentation and mixing are examined in abyssal red clay sediments from the north central pacific using three types of indicators 23 th 232th organic 14c and 137cs and 239 24 pu 23 th 232th analysed revealed that the clay sedimentation rate in three box cores collected within a 50 km radius was less than 1 0 ram 10 3 yr however analyses of the organic carbon in thin layers of sediment revealed that radiocarbon was present much deeper in the cores down to 20 cm than was expected from the 23 th 232th distribution in addition both the stratigraphy and inventory of radiocarbon was significantly different between box cores the distributions and inventories of 137cs and 239 24 pu were similar to that found for radiocarbon further illustrating the spatial variability of radionuclides in oligotrophic north pacific red clays these data suggest that bioturbational processes are important for transporting organic carbon down into the sediment column

the240pu239pu ratio a potential geochronometer abstract the arctic and antarctic ice sheets maintain records of the atmospheric fallout in their datable strata the 240pu239pu ratios in these polar reservoirs uniquely distinguish particulate fallout from the pre moratorium nuclear atmospheric weapons tests dominated by the u s and the post moratorium atmospheric weapons tests dominated by the u s s r thus they offer the possibility of use as a geochronological tool for some marine glacial lacustrine and soil systems

a new ground level fallout record of uranium and plutonium isotopes for northern temperate latitudes plutonium and uranium isotope ratios can be used to differentiate the sources of nuclear contamination from nuclear weapon establishments environ sci technol 34 2000 4496 internal report for awre aldermaston uk 1961 weapon fallout geochim cosmochim acta 51 1987 2623 earth planet sci lett 63 1983 202 earth planet sci lett 22 1974 111 geochim cosmochim acta 64 2000 989 reprocessing plants reactor or satellite accidents science 105 1979 583 science 238 1987 512 and in addition they provide markers for post 1952 geochronology of environmental systems a good record of plutonium and uranium isotope ratios of the background resulting from atmospheric nuclear testing is essential for source characterisation studies using recently developed mass spectrometric techniques j anal at spectrom 16 2001 279 we present here the first complete records between 1952 and the present day of northern temperate latitude 240pu 239pu and 238u 235u atom ratios for atmospheric deposition such information was not derived directly during the period of atmospheric testing because suitable mass spectrometric capability was not available the currently derived records are based on an annual herbage archive and a core from an alpine glacier these studies reveal hitherto unseen fluctuations in the 238u 235u atmospheric fallout record some of which are directly related to nuclear testing in addition they also provide the first evidence that plutonium contamination originating from nevada desert atmospheric weapon tests in 1952 and 1953 extended eastwards as far as northwestern europe the results presented here demonstrate that we now have the capability to detect and precisely identify sources of plutonium in the environment with implications for the development of atmospheric transport models recent geochronology and environmental studies

the 129iodine bomb pulse recorded in mississippi river delta sediments results from isotopes of i pu cs pb and c 129i t1 2 1 56 107 yr has both natural as well as anthropogenic sources anthropogenic sources from nuclear reprocessing discharges and bomb test fallout have completely overwhelmed the natural signal on the surface of the earth in the last 50 years however the transfer functions in and out of environmental compartments are not well known due to temporal variations in the sources of 129i and to a lack of knowledge regarding the forms of iodine from a vertical profile of 129i 127i ratios in sediments located in the mississippi delta region in approximately 60 meters water depth the 129i input function to this region was reconstructed dates in the core were assigned based on the plutonium peak at 20 cm depth assumed to have been deposited in 1963 and the excess 210pb profile in the same depth interval and below that based on the steadily decreasing 240pu 239pu ratios from a ratio of 0 18 at 22 cm to 0 05 at 57 cm depth the 1953 horizon these low 240pu 239pu values are attributed to low yield close in tropospherically transported bomb fallout produced from the nevada test site in the early 1950s which had a value of about 0 035 and strongly suggest a terrestrial source for pu isotopes 129i 127i ratios increased from 2 10 10 at 3 cm to 4 10 10 at 20 cm and from there decreased monotonously to pre anthropogenic values at 53 cm and below 129i concentrations ranged from 8 13 106 atoms g in the top 20 cm and decreased to values of less than 1 106 atoms g below 50 cm atom ratios of 129i 137cs decay corrected to 1962 the year of maximum radionuclide production are about 0 3 very close to the production ratios of about 0 2 during atomic bomb tests this evidence combined with other observations strongly suggests that 129i in mississippi river delta sediments originates from atomic bomb fallout eroded from soils of the mississippi river drainage basin with little alteration of the isotopic ratios during transport from watershed to coastal deposits this is further corroborated by a close correspondence between 129i 127i ratios and other bomb fallout nuclides in this core based on these observations and on laboratory evidence we propose a conceptual model which explains this correspondence and the low 129i 127i ratios found in our sediment core as caused by geochemical i isotope fractionation processes during organic carbon leaching from erodible soils in the mississippi river watershed differences in mobilities of the different chemical forms of 129i and 127i as well as the variances in chemical forms of 129i from nuclear bomb fallout versus nuclear fuel reprocessing are proposed to have created such a correspondence between i isotope ratios and bomb fallout nuclides without revealing recent inputs from nuclear fuel reprocessing releases to the northern hemisphere observed in watersheds of the usa and europe

239 240pu and excess210pb inventories along the shelf and slope of the northeast u s a abstract sedimentary pu and excess 210 pb inventory data are examined from a large number of sites along the u s north atlantic shelf and slope from these data an estimate can be made of the magnitude and location of pu and 210 pb accumulation in this region a major feature of the data is a decrease in the pu and 210 pb inventories with water depth which appears to reflect a decrease in the net scavenging of these elements off shore when pu and 210 pb inventories are summed over water depths less than 4000 m in the north atlantic shelf and slope region the sediments can account for 24 8 of the expected pu and 83 15 of the expected 210 pb inputs at water depths greater than 4000 m in this region we find a greater deficiency in the measured inventories of both 210 pb and pu which cannot be accounted for in the shallower sediments this suggests that the northwest atlantic continental margin is not a major site of pu or 210 pb removal and storage when compared to atmospheric in situ and lateral inputs of these radionuclides