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   

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   

Laboratory studies of the diagenesis and mobility of ^239,240pu and ¹³⁷Cs in nearshore sediments     

Edward R. Sholkovitz  J.Kirk Cochran  Anne E. Carey 《Geochimica et cosmochimica acta》1983,47(8):1369-1379

Controlled laboratory experiments have been used to study the diagenetic chemistry of ^239,240Pu ¹³⁷Cs, and ⁵⁵Fe. Experiments using Buzzards Bay sediments in small tanks show that sulfate reduction is accompanied by the production of large pore water concentration gradients of alkalinity, phosphate, ammonia and dissolved organic carbon and the formation of subsurface maxima in Fe and Mn. These pore water profiles demonstrate that bacterially-mediated processes of organic matter degradation and redox reactions can be simulated in the laboratory.A vertical profile of ⁵⁵Fe in pore waters is reported for the first time: it follows the profile of stable Fe and as such has a large (200 dpm/100 kg) subsurface maximum between 2–4 cm depth. Comparison of ⁵⁵Fe/Fe ratios in sediments and pore waters shows that there is preferential solubilization of ⁵⁵Fe over stable Fe.The pore water activities of ^239,240Pu show no gradients within the large uncertainties of the counting statistics, but are two to four times higher than Buzzards Bay seawater (0.05 dpm/100 kg).The activity of ¹³⁷Cs in the pore water profile is constant (40 dpm/100 kg) within the large counting uncertainties and is twice that of Buzzards Bay seawater. Cs-137 does not appear to be involved in diagenetic chemistry but may increase in pore waters as a result of ion exchange reactions.Flux estimates based on the pore water data show that remobilization and transport of ^239,240 Pu in coastal sediments are not significant processes while the transport of ^l37Cs may be.  相似文献   

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   

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   

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   

Mixing and cycling of uranium,thorium and ²¹⁰Pb in Puget Sound sediments     

R. Carpenter  M.L. Peterson  J.T. Bennett  B.L.K. Somayajulu 《Geochimica et cosmochimica acta》1984,48(10):1949-1963

Activity profiles of excess ²³⁴Th, excess ²¹⁰Pb, ²³²Th, ²³⁰Th, ²³⁴U and ²³⁸U, and ^228/232Th ratios determined in eight box cores of sediment from six sites in central Puget Sound provide new insights into the dynamic nature of solid phase mixing in surface sediments, the exchange of ²²⁸Ra and other soluble species across the sediment-water interface, and the cycling of U, Th and ²¹⁰Pb in this coastal zone.Comparison of excess ²³⁴Th inventories in sediments with its production rate in the overlying water column indicates a mean residence time of at most 14 days for particles in the central Puget Sound water column.Surface sediment horizons with excess ²³⁴Th have no excess ²²⁸Th which might be used to ascertain sediment accumulation rates over the past decade. Instead, deficiencies of ²²⁸Th due to loss of soluble ²²⁸Ra from pore water to the overlying water persist to 20–30 cm, revealing that exchange of soluble chemicals between pore and overlying waters reaches these depths in the extensively bioturbated sediments of Puget Sound.Solid phase U isotope concentrations tend to increase by up to a factor of two with depth in sediments, as a result of dissolved U being biologically pumped down into sediments where it is partially removed when conditions become mildly reducing. ²³²Th and ²³⁰Th activities and ^230/232Th ratios are constant with depth in sediments, indicating constant detrital phase compositions and essentially no authigenic ²³⁰Th. Steady state ²¹⁰Pb depositional activities in and fluxes to Puget Sound sediments average only about onehalf those for sediments of the open Washington coast north of the Columbia River mouth, primarily because of a much lower supply of dissolved ²¹⁰Pb in sea waters adverting into Puget Sound.Excess ²³⁴Th profiles in sediments reveal much more detail about the depth dependency, dynamic nature and recent history of solid phase mixing processes than excess ²¹⁰Pb profiles. At least six of eight ²³⁴Th profiles show that mixing within the ²¹⁰Pb-defined surface mixed layer is depth dependent. In three profiles, ²³⁴Th-derived mixing rates are fastest several centimeters below the sediment-water interface, indicating greater macro-benthic activity at these depths. Depth dependent mixing coefficients derived from the best fit of a four layer, advection-diffusion-decay model to the ²³⁴Th data are consistent with ²¹⁰Pb profiles determined for the same sediments, strongly suggesting that ²³⁴Th and ²¹⁰Pb are mixed equivalently and in a multilayered manner.  相似文献   

Transport and sediment accumulation of210Pb and137Cs in two Southeast Alaskan fjords     

Susan F. Sugai 《Estuaries and Coasts》1990,13(4):380-392

Sediment profiles of²¹⁰Pb and¹³⁷Cs in cores collected at increasing distances from the heads of Smeaton Bay and Boca de Quadra fjords indicate that watersheds influence the inventories of radioisotopes present and that the steep topographies of the fjords enhance sediment redistribution. Episodic deposition of terrestrially derived sediment was responsible for roughly 50% of the¹³⁷Cs and 45% of the²¹⁰Pb inventories in shallower (less than 180 m) locations in Wilson and Bakewell arms of Smeaton Bay.²¹⁰Pb sedimentation rates at shallower sites when corrected for episodic deposition were less than sedimentation rates obtained in the deep basins of the fjords where sediment focusing and increased primary productivity in the overlying water column occur. Higher fluxes of dissolved Mn from surficial sediments and subsequent reoxidation in the overlying water may have enhanced scavenging of²¹⁰Pb in basin locations, resulting in higher inventories. Episodic events have occurred frequently in Smeaton Bay and Boca de Quadra suggesting that steady-state conditions with respect to sedimenting particles can be achieved only when averaged over long time periods approaching the time over which¹³⁷Cs and²¹⁰Pb are useful.  相似文献   

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   

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   

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   

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   

Manzala lagoon, Nile delta, Egypt: modern sediment accumulation based on radioactive tracers   总被引：2，自引：0，他引：2  

L. K. Benninger  I. B. Suayah  D. J. Stanley 《Environmental Geology》1998,34(2-3):183-193

 This study was undertaken to determine whether recent anthropogenic changes in the Nile basin have affected the modern rate of sediment accumulation in the Nile delta. Excess ²¹⁰Pb, ¹³⁷Cs, and ^239,240Pu were used to develop a sediment chronology for a core from central Manzala lagoon, the delta sector which has had the highest average rate of sediment accumulation during the Holocene (to about 0.7 cm year^–1). Excess ²¹⁰Pb was detected in the top 32 cm of the core, yielding an accumulation rate of 1.2 cm year^–1, higher than the mean rate for the Holocene. A high ¹³⁷Cs/^239,240Pu ratio requires a reactor source (possibly Chernobyl) for these nuclides. Low concentrations of excess ²¹⁰Pb and weapons-fallout nuclides precluded recognition of changes in sediment accumulation rate in Manzala lagoon during this century and may limit the use of tracer radionuclides for modern sediment chronology in the Nile delta. Received: 18 March 1997 · Accepted: 22 July 1997  相似文献   

Seasonal variations of ²¹⁰Pb and ²¹⁰Po concentrations in an oligotrophic lake     

Robert W Talbot 《Geochimica et cosmochimica acta》1984,48(10):2053-2063

The vertical distribution of ²¹⁰Pb and ²¹⁰Po in the dissolved (<0.4 μm) and the paniculate (>0.4 μm) phases was measured in Crystal Lake, Wisconsin, to examine the spatial and temporal variability during the seasonal cycle of this oligotrophic lake. The concentration of unsupported ²¹⁰Pb in the water column is maintained principally by atmospheric input. However, most of the ²¹⁰Po in Crystal Lake is produced in situ from radioactive decay of ²¹⁰Pb.Mass balance considerations indicated that the removal rates of ²¹⁰Pb and ²¹⁰Po from the water column to the sediment varied temporally by nearly an order of magnitude. During transient periods of high biological productivity, a large net flux of these nuclides into the sediment occurred. In addition, ²¹⁰Pb was rapidly stripped from the water column during fall turnover. It was during these short-lived events that most of the annual net removal of ²¹⁰Pb and ²¹⁰Po occurred. The mean removal residence time was estimated to be 0.095 yr for ²¹⁰Pb and 0.26 yr for ²¹⁰Po. These residence times suggest that there is a difference between ²¹⁰Pb and ²¹⁰Po in the extent of their recycling in the water column. Calculations indicated that there was a cyclic response of the water column ²¹⁰Po inventory corresponding to successive time periods where there was a net loss or net gain. This cycling is attributed to rapid biological removal and subsequent release from the sediment of freshly deposited ²¹⁰Po. For ²¹⁰Pb, replenishment of the water column appeared to occur mainly from atmospheric input.  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   

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   

Anomalous isotopic concentrations in the sea off Southern California     

Louis Brown  Jeffrey Klein  Roy Middleton 《Geochimica et cosmochimica acta》1985,49(1):153-157

Measurements are reported of the ¹⁰Be concentrations in 15 sediments from the sea off southern California. The sedimentation patterns are modelled with a two component system, one component having the high ¹⁰Be concentration of pelagic sediment and the other the low concentration of continental runoff. The pelagic component, brought to the region by the California Current with the Pacific Ocean as reservoir, is very likely the source not only of anomalously high ¹⁰Be deposition but also of similar effects with ²¹⁰¹Pb, ^239,240pu and ²⁴¹Pu.  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   

现代沉积的²¹⁰Pb计年   总被引：74，自引：10，他引：74       下载免费PDF全文

万国江 《第四纪研究》1997,17(3):230-239

²¹⁰Pb具有百年时间尺度沉积计年的重要价值。²¹⁰Pb_ex计年假设：沉积物是封闭系统；进入水体的²¹⁰Pb能有效地转移到沉积物中并不发生沉积后迁移；非过剩²¹⁰Pb与其母体²²⁶Ra保持平衡。²¹⁰Pb_ex计年可用稳定输入通量-稳定沉积物堆积速率模式、常量初始浓度模式或恒定补给速率模式。沉积物柱芯必须保持原态并以0．5～1cm间隔分截；用相应层节²²⁶Ra校正。沉积物表层混合作用及²²²Rn的丢失可能导致顶部²¹⁰Pb_ex异常。季节性缺氧湖泊沉积物顶部可能存在²¹⁰Pb及²¹⁰Po的再迁移。²¹⁰Pb与¹³⁷Cs两种计年方法原理上具有根本差别。²¹⁰Pb，¹³⁷Cs与沉积纹理方法对比是准确计年的重要保证。  相似文献   

Vertical profile of artificial radionuclide concentrations in the Central Arctic Ocean     

Hugh D. Livingston  Stuart L. Kupferman  Vaughan T. Bowen  R.M. Moore 《Geochimica et cosmochimica acta》1984,48(11):2195-2203

The artificial radionuclides ⁹⁰Sr, ¹³⁷Cs, ²³⁸Pu, ^239,240Pu and ²⁴¹Am have been measured in eight water samples collected in 1979, at intervals from surface to bottom, through the ice at the LOREX satellite camp SS near the North Pole. Differences in the concentrations and ratios of these nuclides, compared with values measured, over time, in the various water masses that flow into the Arctic Ocean, can be used as semi-independent checks on rates of flow to the LOREX stations and on residence times in the Arctic Ocean. An unexpected finding was that water labelled with low-level liquid waste from the Windscale plant on the Irish Sea is a major component of the 1500 m LOREX sample, and has reached there in no more than eight to ten years. Even from this one station in the Polar Ocean, estimation of the inventories of the various radionuclides is good enough to emphasize the importance of horizontal advection of the various supply terms to the Arctic.  相似文献