The pore water chemistry of ^239,240Pu and ¹³⁷Cs in sediments of Buzzards Bay,Massachusetts     

E.R. Sholkovitz  D.R. Mann 《Geochimica et cosmochimica acta》1984,48(5):1107-1114

The collection of large volumes of pore water (1–2 liters per 2 cm horizon of sediment) and low level radiochemical measurements of ^239,240Pu and ¹³⁷Cs have been combined to produce the first study of these fallout artificial radionuclides in marine pore waters. Profiles from box cores taken in June and September 1982 from Buzzards Bay, Mass., are reported along with profiles of many diagenetic constituents (i.e. SO₄^2?, alkalinity, Fe, Mn, DOC, and nutrients).The ^239,240Pu pore water profile is characterized by a subsurface maximum of about 0.28 dpm/100 kg lying between 3–11 cm. Overlying seawater, in contrast, has an activity of $\text{0.01 ± 0.02}$ dpm/100 kg. Below about 11 cm, the pore water ^239,240Pu distribution follows that of the solid phase which decreases rapidly with depth. The pore water profiles of ¹³⁷Cs are characterized by a broad and deeply penetrating maximum where activities of about 35–40 dpm/100 kg extend from 3 to 20 cm. Overlying seawater, in contrast, has an activity of 17–24 dpm/100 kg. The ¹³⁷Cs and ^239,240Pu pore water data show that there is preferential downward transport of ¹³⁷Cs and that ^239,240Pu does not have an active diagenetic chemistry and is not significantly mobile in these coastal sediments.  相似文献   

Plutonium, ²⁴¹Am and ¹³⁷Cs ratios,inventories and vertical profiles in Washington and Oregon continental shelf sediments     

T.M. Beasley  R. Carpenter  C.D. Jennings 《Geochimica et cosmochimica acta》1982,46(10):1931-1946

Continental shelf sediments from nine locations off Washington and Oregon have ^239,240Pu inventories which average 8.0 ± 2.6 mCi/km². 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 ¹³⁷Cs 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 ²¹⁰Pb/^239,240Pu 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.  相似文献   

Particle mixing rates in sediments of the eastern equatorial Pacific: Evidence from ²¹⁰Pb, ^239,240Pu and ¹³⁷Cs distributions at MANOP sites     

J.Kirk Cochran 《Geochimica et cosmochimica acta》1985,49(5):1195-1210

Particle mixing rates (D_B) 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 (D_B = 0.03?0.4 cm²/y) than for continuous input at a constant rate (D_B = 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 ${}^{\mathrm{239,240}}\text{Pu}{}^{137}\text{Cs}$ 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 ${}^{\mathrm{239,240}}\text{Pu}{}^{137}\text{Cs}$ 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.  相似文献   

Plutonium and radiocesium in the water column of the Hudson River estuary     

P. Linsalata  H. J. Simpson  C. R. Olsen  N. Cohen  R. M. Trier 《Environmental Geology》1985,7(4):193-204

Isotopes of plutonium (Pu), cesium (Cs), and cobalt (Co) introduced into the Hudson River Estuary from fallout deposition, the erosion of fallout-contaminated surface soils, and nuclear reactor effluent (isotopes of Cs and Co only) have been measured in water column samples collected from 1975 to 1980 Isotopic measurements conducted independently by two research groups utilizing different sampling and analytical techniques have been summarized. The major conclusions drawn from the work are that for water samples collected by the two laboratories over similar time periods, the mean concentrations of nonfilterable^239,240Pu (<0.45 μm) were identical at 0.13 fCi/l, mean concentrations of both¹³⁷Cs and^239,240Pu in suspended particulates were more divergent at 2,270±920 pCi/kg (±1 SD) and 1,430±430 pCi/kg for¹³⁷Cs, and 19±8 pCi/kg and 12±4 pCi/kg for^239,240Pu The behavior of^239,240Pu and¹³⁷Cs within the water column is shown to diverge within brackish waters Specifically, the magnitude of the¹³⁷Cs distribution coefficient (K _d ) can be expressed as an inverse power function of the chloride ion concentrations for chlorinities between 0.1 and 4 g Cl⁻/l No difference in the^239,240PuK _d has been observed between fresh and brackish waters Based on the expected inventories of^239,240Pu and¹³⁷Cs within watershed soils, the current downstream transport of these radionuclides represents fractional mobilization rates on the order of 1–4 (×10⁻⁴) per year  相似文献   

A model for uranium, rhenium, and molybdenum diagenesis in marine sediments based on results from coastal locations     

Jennifer L. Morford  William R. Martin  Caitlin M. Carney 《Geochimica et cosmochimica acta》2009,73(10):2938-462

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Laboratory and field studies of the relative mobility of ^239,240Pu and ²⁴¹Am from lake sediments under oxic and anoxic conditions     

James J. Alberts  Kent A. Orlandini 《Geochimica et cosmochimica acta》1981,45(10):1931-1939

Laboratory extraction experiments and field observations were employed to determine the relative mobility of ^239,240pu and ²⁴¹Am from lake sediments under aerobic and anaerobic conditions. Laboratory investigations show that under aerobic conditions ²⁴¹Am is more readily extracted from Lake Michigan sediments than is ^239,240Pu. Under anaerobic conditions, the extractability of plutonium and americium does not increase significantly relative to aerobic conditions. Field studies indicate that neither element is recycled from the sediment to the overlying water column during anaerobic conditions attendant with thermal stratification. The adsorption of these elements onto sediments does not appear to be correlated with extractable iron, manganese, and organic compounds such as humic and fulvic acids.  相似文献   

东北四海龙湾玛珥湖沉积物纹层计年与¹³⁷Cs、²¹⁰Pb测年   总被引：15，自引：6，他引：15       下载免费PDF全文

储国强  顾兆炎  许冰  刘强  孙青  汉景泰  刘嘉麒 《第四纪研究》2005,25(2):202-207

对东北四海龙湾玛珥湖SHLF6孔纹层沉积物的¹³⁷Cs放射性测量表明:¹³⁷Cs比活度的最大值出现在55cm处,对应于1963年世界原子弹试爆高峰期。纹层计年表明0～6cm共有35个纹层层偶。从75cm到65cm,¹³⁷Cs比活度从256±009dpm/g急剧增加到1868±017dpm/g,可能65cm对应于1954年。通过测量²²⁶Ra子核²¹⁴Pb和²¹⁴Bi（能量为295keV,352keV和609keV）放射的光子数获得²²⁶Ra比活度数据,然后求得过剩²¹⁰Pb_{比活度（²¹⁰Pbuns）。²¹⁰Pbuns比活度随深度增加而呈指数衰减,其异常波动可能与人类活动以及沉积速率变化有关,例如55cm处²¹⁰Pb比活度较高,与¹³⁷Cs的峰值对应,这可能与1963年前后人工核实验的高峰有关,因为核试验不仅产生¹³⁷Cs,而且可以产生208Pb和²¹⁰Pb;45cm处²¹⁰Pb比活度较低,而²²⁶Ra较高,可能与人类活动加剧,导致沉积速率增加有关。根据²¹⁰PbunsCRS模式,SHLF6孔0～19cm的平均沉积速率为20mg/cm²·a,或约为011cm/a。²¹⁰Pb测年数据与¹³⁷Cs时标及纹层计年均有很好的一致性。四海龙湾玛珥湖发育的纹层为年纹层,可以建立高分辨率时间序列。}  相似文献   

Transport and accumulation of actinide elements in the near-shore environment: field and modelling studies   总被引：2，自引：0，他引：2  

OLIVIA J. MARSDEN†  LIAM ABRAHAMSEN†  NICHOLAS D. BRYAN†  J. PHILIP DAY†  L. KEITH FIFIELD‡  CLARISSA GENT†  PHILLIP S. GOODALL§  KATHERINE MORRIS¶  FRANCIS R. LIVENS 《Sedimentology》2006,53(1):237-248

Nuclear facilities in coastal locations often discharge low‐level liquid wastes into the sea and the radioisotopes in these discharges are of interest both in assessing possible environmental impacts and as tracers for coastal processes. The distributions of a range of artificial radionuclides, derived from the authorized discharges from British Nuclear Fuels (BNFL) Sellafield, have been determined in the sediments of an intertidal salt marsh in the Esk Estuary, Cumbria, UK. Where published discharge histories exist (for ¹³⁷Cs, ²³⁸Pu, ^239,240Pu and ²⁴¹Am), the sediment core‐profile distributions of these radionuclides have been compared with the releases from Sellafield, and consistent values of the accumulation rate (0·226 ± 0·007 g cm^?2 yr^?1) are obtained. A quantitative model has been developed, describing association of radionuclides with suspended particulate material, which is then accumulated and mixed in an offshore mud patch before resuspension and deposition in the salt marsh. The model has been used to describe radionuclide distributions observed in both the mud patch and the salt marsh, and to identify isotopes for which post‐depositional remobilization or solution transport from the discharge point are important. The behaviour of the commonly studied isotopes (¹³⁷Cs, ²³⁸Pu, ^239,240Pu and ²⁴¹Am) is similar to that observed at this and other nearby locations. The activation product isotope ²³⁶U is enhanced in these sediments over the natural baseline by four to eight orders of magnitude, and the results suggest that Sellafield‐derived uranium is comparably mobile to ¹³⁷Cs in these sediments although the processes governing the behaviour of these two elements may be different. In situ production of ²⁴¹Am by decay of its ²⁴¹Pu parent has generated only 17% of the current sediment inventory of this isotope, insufficient to account for the increase over the last 20–25 years, and suggesting that the input material for these sediments is preferentially enriched in Am relative to Pu during transport from the offshore mud patch. The discharge history of ²⁴⁴Cm, which is unknown, has also been reconstructed from the sediment profile and the model.  相似文献   

Comparative ²¹⁰Pb, ¹³⁷Cs,and pollen geochronologies of sediments from Lakes Ontario and Erie     

J.A. Robbins  D.N. Edgington  A.L.W. Kemp 《Quaternary Research》1978,10(2):256-278

The distribution of ²¹⁰Pb, ¹³⁷Cs, and Ambrosia (ragweed) pollen in two sediment cores from Lake Ontario and in three cores from Lake Erie provides independent estimates of sediment accumulation rates. Geochronology with ²¹⁰Pb is based on radioactive decay of the isotope following burial in sediments. The method can reveal with precision changes in sedimentation occurring over the past 100 yr or so. Geochronologies with ¹³⁷Cs and Ambrosia are based on the occurrence of a horizon corresponding, respectively, to the onset of nuclear testing 25 yr ago and to regional forest clearance in the middle 1800s. These methods provide estimates of long-term average sediment accumulation rates. In all but one core, the distributions of ¹³⁷Cs and ²¹⁰Pb indicate no physical mixing of near-surface sediments. In two cores, including one from central Lake Erie collected by diver, all three estimates of sedimentation rates are in excellent agreement. In two other cores, rates based on ²¹⁰Pb are significantly higher than those inferred from Ambrosia pollen profiles. Lower average rates appear to result from occasional massive losses of sediments. Such events, apparent in the distribution of ²¹⁰Pb but not in pollen records, correlate with the occurrence of major storm surges on the lakes during this century. In one core from western Lake Erie, exponential distributions of both ²¹⁰Pb and Ambrosia appear to be artifacts which may result from extensive biological or physical reworking of sediments in shallow water (11 m). Previous indications of increased sedimentation in Lake Erie since about 1935 based on Castanea (chestnut) pollen data are not substantiated.  相似文献   

Historical trace element distribution in sediments from the Mississippi River delta     

Peter W. Swarzenski  Mark Baskaran  Robert J. Rosenbauer  William H. Orem 《Estuaries and Coasts》2006,29(6):1094-1107

Five sediment cores were collected on the shelf of the inner Mississippi Bight in June 2003 for a suite of radionuclides to establish geochronologies and trace elements to examine patterns of contaminant deposition and accumulation. Core sites were chosen to reflect a matrix of variable water depths, proximity to the Mississippi River mouth as the primary source for terrigenous particles, and extent and duration of summertime water column hypoxia. The vertical distribution of^239,240Pu and²¹⁰Pb_xs(=²¹⁰Pb_total−²²⁶Ra) provided reliable geochronological age constraints to develop models for mass accumulation rates and historic trace element inputs and variations. Mass accumulation rates ranged from 0.27 to 0.87 g cm⁻²yr⁻¹ and were internally consistent using either²¹⁰Pb_xs or^239,240Pu. Measured inventories of¹³⁷Cs,^239,240Pu, and²¹⁰Pb_xs were compared to atmospheric deposition rates to quantify potential sediment focusing or winnowing. Observed variability in calculated mass accumulation rates may be attributed foremost to site-specific proximity to the river mouth (i.e., sediment source), variability in water depth, and enhanced sediment focusing at the Mississippi River canyon site. Trace element concentrations were first normalized to Al, and then Al-normalized enrichment factors (ANEF) were calculated based on preanthropogenic and crustal trace element abundances. These ANEFs were typically >1 for V and Ba, while for most other elements studied, either no enrichment or depletion was observed. The enrichment of Ba may be related, in part, to the seasonal occurrence of oxygen-depleted subsurface waters off the Mississippi River delta, as well as being an ubiquitous byproduct of the petroleum industry.  相似文献   

Plutonium and americium in anoxic marine sediments: Evidence against remobitization     

R. Carpenter  T.M. Beasley 《Geochimica et cosmochimica acta》1981,45(10):1917-1930

^{239 + 240}Pu activities of 100–450dpm/kg are found down to 15–18 cm in anoxic Saanich Inlet sediments, with a subsurface maximum in undisturbed deposits. Integrated ^{239 + 240}Pu inventories which overlap delivery estimates are present both in two cores of anoxic sediments from Saanich Inlet and in one core of oxic sediments 65 km away in Dabob Bay, Washington. ${}^{241}\text{Am}{}^{\mathrm{239\; +\; 240}}\text{Pu}$ ratios in Saanich Inlet sediments overlap ratios in unfractionated midnorthern latitude fallout, in oxic sediments from the Washington continental shelf, and in anoxic sediments from two basins off southern California and Mexico. The ${}^{\mathrm{239\; +\; 240}}\text{Pu}{}^{137}\text{Cs}$ ratios in three intervals of Saanich Inlet sediments are also in agreement with ratios previously reported for oxic coastal marine sediments. The Pu inventories, the $\text{Am}\text{Pu}$ and $\text{Pu}\text{Cs}$ ratios, and the Saanich Inlet Dabob Bay comparison all argue that Pu is not rapidly remobilized in anoxic sediments.The subsurface ^{239 + 240}Pu activity maximum is not in agreement with the historical record of peak Pu fallout in 1963–1964 unless our ²¹⁰Pb-derived sedimentation rates are incorrectly high. However, they are in good agreement with previous ²¹⁰Pb and varve chronologies in Saanich Inlet, and also give reasonable dates for times when ^{239 + 240}Pu and SNAP-9A supplied ²³⁸Pu first appear in the sediments. We conclude they properly date the maximum in sedimentary ^{239 + 240}Pu activity at 1970–1973, and seek explanations for the 7–10yr time lag after peak fallout.^{239 + 240}Pu inventories in one core from the eastern basin of the Cariaco Trench and in two cores from Golfo Dulce. an anoxic basin off the Pacific coast of Costa Rica, are also in reasonable agreement with fallout delivery to these latitudes when excess ²¹⁰Pb inventories and fluxes are used to verify recovery of at least a major fraction of the most recently deposited sediments.  相似文献   

Downward migration of Chernobyl-derived radionuclides in soils in Poland and Sweden   总被引：1，自引：0，他引：1  

Gerald Matisoff  Michael E. KettererKlas Rosén  Jerzy W. MietelskiLauren F. Vitko  Henning PerssonEdyta Lokas 《Applied Geochemistry》2011,26(1):105-115

Vertical profiles of ¹³⁷Cs and ^239,240Pu were measured in soils collected from two sites in southern Sweden and three sites in southern Poland and were modeled using both a solute transport model and a bioturbation model to better understand their downward migration. A time series of measured ¹³⁷Cs profiles indicates that ¹³⁷Cs from Chernobyl was found at the soil surface in 1986 but it has migrated progressively downward into the soil 4.5-25.5 cm since. However, because of dispersion during the migration and mixing following Chernobyl deposition and the much higher activities of ¹³⁷Cs from Chernobyl, stratospheric fallout of ¹³⁷Cs from the 1960s cannot be identified as a second ¹³⁷Cs activity maximum lower in the soil column at any of the sites. Conversely, the ²⁴⁰Pu/²³⁹Pu ratio indicates that no Chernobyl-derived Pu is present in any of the cores with the exception of one sample in Sweden. This difference may be attributed to the nature of the release from Chernobyl. Cesium volatilized at the reactor temperature during the accident, and was released as a vapor whereas Pu was not volatile and was only released in the form of minute fuel particles that traveled regionally. Both the solute diffusion and the bioturbation models accurately simulate the downward migration of the radionuclides at some sites but poorly describe the distributions at other sites. The distribution coefficients required by the solute transport model are about 100 times lower than reported values from the literature indicating that even though the solute transport model can simulate the profile shapes, transport as a solute is not the primary mechanism governing the downward migration of either Cs or Pu. The bioturbation model uses reported values from the literature of the distribution coefficients and can simulate the downward migration because that model buries the fallout by placing soil from depth on top and mixing it slightly throughout the mixing zone (0.6-2% per year of mixing). However, mixing in that model predicts concentrations in the top parts of the soil profiles which are too high in many cases. Future progress at understanding the downward migration of radionuclides and other tracers will require a more comprehensive approach, combining solute transport with bioturbation and including other important soil processes.  相似文献   

The geochemistry of fallout plutonium in the North Atlantic: I. A pore water study in shelf,slope and deep-sea sediments     

《Geochimica et cosmochimica acta》1987,51(10):2605-2622

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²¹⁰Pb activities in and fluxes to sediments of the Washington continental slope and shelf     

R. Carpenter  J.T. Bennett  M.L. Peterson 《Geochimica et cosmochimica acta》1981,45(7):1155-1172

Surface sediments of the Washington coast have ²¹⁰Pb activites which average 104 ± 48dpm/g for submarine canyon and slope regimes and 18 ± 12dpm/g for the continental shelf regime. ²¹⁰Pb sedimentary fluxes are also higher in canyons, averaging 18 ± 13dpm/cm² per yr, compared to 5.2 ± 3.1 dpm/cm² per yr for slope and 4.8 ± 1.8dpm/cm² per year for shelf regions. These ²¹⁰Pb activities and fluxes are 2–7 times greater than those reported for other coastal regions. Inputs from the atmosphere and the Columbia River are not sufficient to supply the ²¹⁰Pb, but advection of seawater containing dissolved ²¹⁰Pb produced in situ from ²²⁶Ra provides an input several times larger than the sedimentary fluxes. The sedimentary ²¹⁰Pb flux is limited by scavenging reactions rather than by supply of dissolved ²¹⁰Pb.Calculations of maximum biological uptake and fluxes of ²¹⁰Pb and ‘selective’ chemical leaching experiments all show that the primary scavenging processes are due to hydrous Mn and Fe oxides rather than biological phases. The pattern of higher ²¹⁰Pb depositional fluxes in canyons than in nearby open slope areas of comparable water depth is most reasonably explained by enhanced scavenging of dissolved ²¹⁰Pb near the sea floor, rather than by processes operating throughout the water column. Relatively rapid removal of dissolved ²¹⁰Pb from the near bottom nepheloid layer to slope and canyon sediments is shown by its mean residence time of less than two years in this layer.  相似文献   

The relative mobility of natural (Th,Pb and Po) and fallout (Pu,Am, Cs) radionuclides in the coastal marine environment: results from model ecosystems (MERL) and Narragansett Bay     

Peter H Santschi  Yuan-Hui Li  Dennis M Adler  Michael Amdurer  Joy Bell  Urs P Nyffeler 《Geochimica et cosmochimica acta》1983,47(2):201-210

The relative mobility of nuclides of Pb, Th, Pu, and Cs, which are widely used as geochemical tracers for sedimentation and bioturbation. was investigated in artificial microcosm tanks (MERL) and in Narragansett Bay. Their mobility was characterized by their removal rates from the water column, their affinity toward particles and their degree of penetration into the surface sediments. Pb, Th, and Pu transport was controlled predominantly by the affinity of these elements to particles, and the transport parameters of the particles themselves (i.e. sediment resuspension and mixing rates). Because of its low distribution coefficient, transport of Cs was controlled by molecular diffusion through pore water in the winter, while in summer, Cs transport was enhanced due to bioturbation. The increase with depth of the $\text{Cs}\text{Pu}$ ratio in core profiles of MERL and Narragansett Bay sediments is thus caused primarily by the higher mobility of Cs.  相似文献   

Annual cycle of radionuclide contamination on tide-washed pasture in the Mersey Estuary, NW England     

Michael S. Johnson  David Copplestone  Winston M. Fox  Steve R. Jones 《Estuaries and Coasts》2001,24(2):198-203

The radionuclide burden of vegetation comprising a tide-washed pasture at Ince Marsh in the Mersey Estuary, U.K., derives mainly from adhered external particulates originating as suspended sediments in estuarine water. Radionuclide concentrations are dominated by the growth cycle of the vegetation, with the highest winter levels of contamination activity an order of magnitude greater than the lowest levels in mid-summer. A secondary effect due to sediment transfer during periods of severe flooding produces subsidiary features on this dominant seasonal profile. Radionuclide concentrations on vegetation are in the range¹³⁷Cs=8–191,¹³⁴Cs=0.3–0.9,²⁴¹Am=0.6–46,²³⁸Pu=0.1–1.5, and^239/240Pu=0.8–44 Bq kg⁻¹. These ranges reflect the relative concentrations of radionuclides in estuarine sediment (¹³⁷Cs=615,²⁴¹Am=202, and^239/240Pu=104 Bq kg⁻¹) rather than the values in filtered estuary water (¹³⁷Cs=0.4,²⁴¹Am=0.001, and^239/240Pu=0.001 Bq 1⁻¹). Median K_d values for these radionuclide species are Cs=1,400, Am=200,000, and Pu=80,000 1 kg⁻¹).  相似文献   

Mg,Ca and $\text{O}{}^{18}\text{O}{}^{16}$ exchange in the sediment-pore water system,hole 149, DSDP     

Edward A. Perry  J.M. Gieskes  J.R. Lawrence 《Geochimica et cosmochimica acta》1976,40(4):413-423

The diagenesis and geochemical evolution of deep-sea sediments are controlled by the interaction between sediments and their associated pore waters. With increasing depth, the pore water of Hole 149 (DSDP) exhibits a strong depletion in Mg and a corresponding enrichment in Ca, while the alkalinity remains relatively constant. Dissolved SiO₂ is nearly constant in the upper 100 m of sediment, but is highly enriched in the deepest pore waters. The pore waters exhibit a depletion in K with increasing depth, and $\text{O}{}^{18}\text{O}{}^{16}$ pore water ratios also decrease.The sediment section has three zones of sedimentary regimes with increasing depth in the drill hole: an upper 100 m section of detrital clays, a middle section enriched in calc-akalic volcanics which have undergone submarine weathering to a smectite phase, and a lower section of siliceous ooze which still has a diagenetic smectite phase. The quartz-feldspar ratios and $\text{O}{}^{18}\text{O}{}^{16}$ composition of the silicate phases are in agreement with these interpretations.The submarine weathering of volcanics to a smectite can account for the observed pore water gradients. Volcanics release Ca and Mg to the pore waters causing the alkalinity values to increase. Smectite is formed, depletes the pore waters in Mg and O¹⁸ and causes the alkalinity to decrease. The net reaction allows for the observed relationship between pore water Ca and Mg gradients with little net change in alkalinity. Given the abundance of volcanics in many deep-sea sediments, especially in lower sections which often form near ridge crests, the submarine formation of smectite may be an additional oceanic Mg sink which has not yet been fully considered.  相似文献   

Assessment of ¹³⁷Cs and ⁹⁰Sr fluxes in the Barents Sea     

G. G. Matishov  D. G. Matishov  I. S. Usyagina  N. E. Kasatkina  E. V. Pavel’skaya 《Doklady Earth Sciences》2011,439(2):1190-1195

The annual balance of radionuclides inflow/outflow was assessed for ¹³⁷Cs and ⁹⁰Sr isotopes in the Barents Sea, taking into account the atmospheric precipitation, inflow from the Norwegian and the White seas, as well as riverine discharge, liquid radioactive waste disposal (LRWD), and outflow to the adjacent seas. The original and published data for the period of 1950–2009 were analyzed. According to the multiyear dynamics (1960–2009), the inflow of ¹³⁷Cs and ⁹⁰Sr into the Barents Sea was significantly preconditioned by the Norwegian Sea currents; and precipitation played a major role in the 1950s, 1960s, and in 1986. Currently, the trans-border redeposition of ⁹⁰Sr prevails over ¹³⁷Cs redeposition in the Barents Sea, and constitutes about 99% of inflow of each element.  相似文献   

Natural decrease of the intensity level of artificial radioactive isotopes in the Barents Sea     

Matishov  G. G.  Matishov  D. G.  Solatie  D.  Kasatkina  N. E.  Leppanen  A. 《Doklady Earth Sciences》2009,427(2):1006-1011

The results of radioecological investigations carried out within the framework of the Russian-Finnish high-latitude expedition in 2007 are presented. The characteristics of the present-day accumulation level of the significant radioecological isotopes ¹³⁷Cs, ⁹⁰Sr and ^239,240Pu in the Barents Sea are described. The comparative analysis is performed for the radiation pollution of the environment in the 1980s and 1990s and in the first decade of the 21st century. Natural purification processes in the marine environment are the main factors of the decrease in the intensity level of artificial radioactive isotopes. These processes include repeated dilution, nuclear decay, occlusion by sediments and suspended solid material, and accumulation by aquatic inhabitants. A stable decreasing trend is observed for the intensity level of artificial radioactive isotopes in the Barents Sea.  相似文献   

Ice accumulation rate in Changme-Khangpu glacier,Sikkim     

P. N. Shukla  N. Bhandari  V. N. Nijampurkar  D. Kameswara Rao  V. M. K. Puri  Sanjiv Sharma 《Journal of Earth System Science》1983,92(3):255-260

Vertical profiles of¹³⁷Cs and²¹⁰Pb have been determined in a 9 m column of ice from accumulation zone of Changme-Khangpu glacier in north Sikkim valley.¹³⁷Cs activity varies from 4 to 22 dpm/ L. In many samples²¹⁰Pb occurs at a level of 20 to 65 dpm/ L which is much higher than the expected fallout value.¹³⁷Cs and²¹⁰Pb activities correlate well with each other but not with the dust content. Possibility of²¹⁰Pb production in the nuclear explosions is discussed. Several peaks appear in the depth profile of¹³⁷Cs and²¹⁰Pb which can be matched with Chinese atmospheric nuclear explosions with some phase difference if a uniform ice accumulation rate of 0.7 m per year is assumed since 1969.  相似文献