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 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   

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   

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   

Cycling of fallout (Pu, 241Am, 137Cs) and natural (U,Th, 210Pb) radionuclides in Washington continental slope sediments     

《Geochimica et cosmochimica acta》1987,51(7):1897-1921

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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   

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   

Sr and Pb isotopes,U and Th chemistry of the alkaline Monteregian and White Mountain igneous provinces,eastern North America     

G.Nelson Eby 《Geochimica et cosmochimica acta》1985,49(5):1143-1153

The Monteregian Hills and younger White Mountain alkaline intrusions were emplaced into the Cambro-Ordovician sediments of the St. Lawrence Lowlands and the folded and thrusted Lower Paleozoic sequence of the Appalachian orogen. Age relations indicate that there is a fine-scale structure to the igneous activity, with slightly undersaturated to critically saturated rocks emplaced between 141 and 128 Ma and strongly undersaturated rocks emplaced between 121 and 117 Ma.Sr and Pb isotopic data for the mantle-derived alkali picrite, alkali olivine basalt and basanite magmas, indicate derivation from a depleted mantle similar to that which produces present-day oceanic island basalts. For the most isotopically primitive samples, decay-corrected ${}^{87}\text{Sr}{}^{86}\text{Sr}\text{= 0.7030–0.7037}$, ${}^{206}\text{Pb}{}^{204}\text{Pb}\text{= 19.05–19.72}$, ${}^{207}\text{Pb}{}^{204}\text{Pb}\text{= 15.56–15.65}$, and ${}^{208}\text{Pb}{}^{204}\text{Pb}\text{= 38.64–39.26}$. On Pb-Sr isotope correlation diagrams the data define trends similar to those for MOR basalts, implying mantle heterogeneity which requires the presence of a component enriched in radiogenic Pb relative to Sr. The interaction of these isotopically primitive magmas with the crust can be defined in terms of a three component system: depleted mantle-Grenville age crust-Lower Paleozoic age crust. The granitic magmas were apparently derived from the Lower Paleozoic crust of the Appalachian orogen.For the mantle-derived magmas, Th/U ratios vary from 2.5 (estimated ratio for MORB source) to 5.1, with the mean value near that of the bulk earth. The variations in Th/U suggest mantle heterogeneity on a local scale, and the high Th/U of some samples suggests that the mantle was enriched in incompatible elements shortly before melting. The magmas derived by partial melting of the crust have Th/U of 3.3 to 8.7, and the higher ratios are associated with rocks crystallized from magmas that originated by melting of Lower Paleozoic sediments.The Sr and Pb isotopic data support the conclusion of Bellet al. (1982) that the subcontinental mantle under eastern Canada underwent a Precambrian depletion event. This depleted mantle apparently extends under the White Mountain province and is isotopically similar to the mantle which gives rise to oceanic island basalts. In contrast, Pb isotopic ratios for the New England Seamount chain (TARAS and HART, 1983), which apparently represents the oceanic extension of this magmatic activity, are significantly more radiogenic. It is possible that a mantle plume provided the heat energy, and perhaps metasomatic fluids, to trigger melting in the subcontinental mantle, whereas in the case of the oceanic extension the plume directly contributed to the observed magmatism, as reflected in the more radiogenic Pb ratios.  相似文献   

Isotopic and incompatible element constraints on the genesis of island arc volcanics from Cold Bay and Amak Island,Aleutians, and implications for mantle structure     

J.D Morris  S.R Hart 《Geochimica et cosmochimica acta》1983,47(11):2015-2030

Cold Bay and Amak Island, two Quaternary volcanic centers in the eastern Aleutians, are orthogonal relative to the trench and separated by ~50 km. Sr, Nd and Pb isotopic compositions of the calc-alkaline andesite magmas show no sign of contamination from continental crust (average ${}^{87}\text{Sr}{}^{86}\text{Sr}\text{= 0.70323}$, ${}^{143}\text{Nd}{}^{144}\text{Nd}\text{= 0.51301}$, ${}^{206}\text{Pb}{}^{204}\text{Pb}\text{= 18.82}$, ${}^{207}\text{Pb}{}^{204}\text{Pb}\text{= 15.571}$). These samples plot within the mantle arrays for Sr-Nd and for Pb and are similar to arcs such as the Marianas and New Britain (Sr-Nd) and Marianas and Tonga (Pb). Incompatible element ratios for the Aleutian andesites (K/Rb ~ 332, K/Cs ~ 10,600, K/Sr ~ 22.4, K/Ba ~ 18.3, Ba/La ~ 60) are within the range reported for arc basalts, despite the difference in degree of fractionation.Average K content, K/Rb, K/Ba and K/Sr are approximately the same for basalts from arcs and from oceanic islands (OIB); K/Cs is a factor of 4 lower and Ba/La almost 3 times higher in arcs. Abundance ratio correlations indicate that arcs are enriched in Cs and depleted in La relative to OIB, with other incompatible element abundances very similar. Histograms of Sr and Nd isotopic compositions for MORB, OIB, and intraoceanic arcs show remarkably similar peaks and distribution patterns for intraoceanic arcs and OIB.A “plum pudding” model for the upper mantle best accommodates a) geochemical coherence of OIB and IAV, b) the existence of mantle plumes at some oceanic islands, and c) the presence of a MORB-type source at back arc spreading centers. In this model, OIB plums are imbedded in a MORB matrix; small degrees of melting generate OIB-type magmas while larger degrees of melting dilute the OIB magma with MORB matrix melts.OIB plums are merely less robust lower mantle plumes (i.e., blobs) which are distributed throughout the upper mantle by convection. The existence of at least two types of OIB, as indicated by Sr, Nd, and Pb isotopes, suggests that nuggets of recycled oceanic lithosphère may coexist with lower-mantle plums and that both may be tapped in arcs and intraplate environments.  相似文献   

A kinetic approach to describe trace-element distribution between particles and solution in natural aquatic systems     

Urs P Nyffeler  Yuan-Hui Li  Peter H Santschi 《Geochimica et cosmochimica acta》1984,48(7):1513-1522

The partitioning of radioactive trace elements between seawater and particulate matter from surface sediments and sediment traps was investigated in laboratory experiments. For the elements Na, Zn, Se, Sr, Cd, Sn, Sb, Cs, Ba, Hg, Th and Pa (group I) constant distribution coefficients (K_d) were found after a few days of equilibration, whereas the elements Be, Mn, Co and Fe (group II) showed an increasing K_d over the whole time of observation of 108 days. The time dependence of K_d is described by an adsorption-desorption equilibrium (group I elements), followed by a lattice transport reaction step (group II elements). The reaction rate constants are compared to Mn oxidation rates and to adsorption rate constants derived from in situ measurements of the $\text{U}\text{Th}$ disequilibrium as available from literature.  相似文献   

Trace element inventory for the northern Chesapeake Bay with emphasis on the influence of man     

G.R Helz 《Geochimica et cosmochimica acta》1976,40(6):573-580

For the northern half of the Chesapeake Bay. Maryland, an evaluation has been made of the relative importance of various human and natural sources of Cr, Mn, Fe, Co, Ni, Cu, Cd, Zn, and Pb. For rive of these (Mn, Fe, Co, Ni, and Zn) river discharge, shore erosion and salt water advection from the oceans account for more than half of the total input. On the other hand, the principal source for Cr and Cu is direct industrial discharge, for Cd is municipal wastewater, and for Pb is atmospheric dust and rain. In the subestuary of Baltimore Harbor, industry is the major contributor of all the elements except Cd and Pb, which again come mostly from wastewater and the atmosphere, respectively. Estimates of the removal of these elements by sedimentation suggest that less than $\text{1}\text{3}$ of the annual input of each metal is removed, except in the case of Cr and Fe where more than $\text{2}\text{3}$ is removed. These results suggest that human enhancement of normal input rates for these elements has the potential to produce a regional rather than merely a local biologic impact. It is of interest that for most of the elements, the percentage of the total input that is retained in the sediments is similar for heavily stressed Baltimore Harbor as it is for the northern Bay system as a whole.  相似文献   

Radiocarbon age inversions and progression: source and causes in Late Holocene sediments from Lake Chapala,western Mexico   总被引：1，自引：0，他引：1  

Pedro F. Zárate-del-Valle  Hermes U. Ramírez-Sánchez  François Fernex  Bernd R. T. Simoneit  Isabel Israde-Alcántara 《Environmental Earth Sciences》2011,63(5):1011-1019

The results of eight radiocarbon datings of Lake Chapala sediments (site T46) are presented, the age inversions (AI) observed and their age progression discussed. As deduced from some AIs and the ²¹⁰Pb activity (site CHP4), the bioturbation zone in the lake varies over a depth of 5–25 cm. The linear sedimentation rates (LSRs) calculated from ¹⁴C ages do not match the LSR calculated from unsupported ²¹⁰Pb activity for the upper sediments. This demonstrates the usefulness of dating sediments with complementary radiometric techniques such as short-lived isotope counting (SLIC), i.e., ²¹⁰Pb and ¹³⁷Cs. This approach leads to the following conclusions: (1) The incorporation of detrital particles with ancient carbon into the sedimentary column of the lake occurred by a combination of: (a) the presence of outcrops of hydrothermal petroleum with ages >40 ka (ka = thousands of years) in the lake, and (b) mass transport due to the presence of two elongated gyre circulation patterns integrated by cyclonic circulation (counterclockwise) in the north portion of the lake and anticyclonic circulation in the southern part. (2) Consequently, the ¹⁴C ages of shallow lake sediments have geologic ages one order of magnitude greater compared to their ages determined by the ²¹⁰Pb method. (3) A bioturbation mechanism is not necessary to explain the ¹⁴C AI in the top 70 cm and from 110 to 150 cm depth of the sediments. (4) According to the biological proxies data for the last 600 years B.P., the paleoclimate at Lake Chapala has changed from sub-humid to dry environmental conditions, and eutrophication has increased over the past 100 years due to local input from ongoing agricultural activities.  相似文献   

Actinide microdistributions in the enstatite meteorites     

M.T. Murrell  D.S. Burnett 《Geochimica et cosmochimica acta》1982,46(12):2453-2460

Oldhamite is a major Th and U bearing phase in the enstatite meteorites. Oldhamite from E-6 chondrites has mean Th and U abundances of 1550 ± 80 ppb Th and 410 ± 20 ppb U, with $\text{Th}\text{U}\text{= 3.8 ± .2}$. With the exception of ferroan alabandite which contains 25 ± 1 ppb U, no other Th or U enriched phases were located in the E-6 chondrites, and nearly all of the total rock Th and U can be accounted for by oldhamite. In Khairpur (E6), excess fossil fission tracks were observed in enstatite grains in contact with oldhamite which indicates the presence of ²⁴⁴Pu in oldhamite. Oldhamite from St. Mark's (E5) and Abee (E4) also shows actinide enrichments but at levels about half the E-6 results. Niningerite in Abee contains 45 ± 5 ppb U and due to its high reported modal abundance is an important U reservoir in Abee. The U content of oldhamite from the aubrite Peña Blanca Spring is 1920 ± 100 ppb. All $\text{Th}\text{U}$ values measured in this study cluster tightly around a value of 4 which indicates a lack of ThU fractionation in both oldhamite and in the enstatite meteorites, themselves. This lack of fractionation, along with the presence of ²⁴⁴Pu in oldhamite and reported rare earth enrichments also in oldhamite, suggests that the enstatite chondrites may be well-suited for PuU chronology and for providing the initial PuU value in the early solar system.  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   

Changes of lead and barium with time in California off-shore basin sediments     

Amy No  Clair C. Patterson 《Geochimica et cosmochimica acta》1982,46(11):2307-2321

During ancient times the natural deposition fluxes of lead which can be leached with dilute acid from sediments in Santa Barbara, Santa Monica and San Pedro basins offshore from the Los Angeles Urban complex, were about 0.7, 0.1 and 0.2 μg Pb/cm² yr respectively. Since there was little difference in biological productivity in surface waters of these basins, it is proposed that clay is a major transport vehicle for sequestered soluble lead, which then explains why the lead deposition flux within the Santa Barbara basin was so much larger compared to the other basins. The fluxes of silicate mud in the basins in ancient times were about 92, 19 and 30 mg/cm² yr in Santa Barbara, Santa Monica and San Pedro basins respectively. Today deposition fluxes of acid soluble lead within these three basins are 3- to 9-fold greater, being about 2.1, 1.1 and 1.8 μg Pb/cm² yr respectively, partly in the form of directly deposited large sewage particles, which account for none, $\text{2}\text{3}$ and $\text{3}\text{4}$ of the total industrial lead deposition fluxes in the respective basins. Concentrations of leachable lead in varve dated sediment layers increase with time and isotopic compositions of these leads change in accordance with corresponding known changes of isotopic compositions of industrial lead in the Los Angeles atmosphere. Lead remaining in acid leached sediment residues originates from igneous and clay minerals, exhibiting no change in concentration or isotopic composition since pre-industrial times.Deposition fluxes of total barium in sediments among the three basins were proportional to mass deposition fluxes before 1950 in the same manner as for lead. Afterwards, there are barium concentration maxima with time in both Santa Monica and San Pedro Basin sediments which are attributable to industrial sewage rather than to episodic erosion from barium-rich sedimentary evaporite strata exposed locally along the shore. An increase of barium concentrations in present day Santa Barbara basin sediments may reflect dispersal of barium-rich drilling mud from local drilling operations.  相似文献   

Geochemical investigations of the origin of the Manaslu leucogranite (Himalaya,Nepal)   总被引：1，自引：0，他引：1  

Ph. Vidal  A. Cocherie  P. Le Fort 《Geochimica et cosmochimica acta》1982,46(11):2279-2292

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${}^{207}\text{Pb}{}^{206}\text{Pb}$ ages of individual mineral phases in Luna 20 material by ion microprobe mass analysis     

C.A Andersen  J.R Hinthorne 《Geochimica et cosmochimica acta》1973,37(4):745-754

Ion microprobe analyses of returned lunar material have helped to demonstrate that U, Th and radiogenic Pb are concentrated in small accessory mineral phases. It is possible to measure the isotopic composition of this Pb and obtain a radiometric ${}^{207}\text{Pb}{}^{206}\text{Pb}$ age for the mineral. The ages so derived compare favorably with crystallization ages determined by conventional methods. A grain mount ($\text{22003,2}\text{6}$) of Luna 20 material was searched for such accessory mineral phases and two were found. One of these phases gives an age of 4.12 ± 0.04 b.y. and the other an age of 4.42 ± 0.11 b.y. Ages of minerals dated by the ion probe in Apollo samples 14310 and 15555 are given for comparison. Data on the upper limit for Pb concentration in the outermost surface layers of free lunar soil particles are also given.  相似文献   

Population density, prey selection, and predator avoidance of the burrowing anemone (Ceriantheopsis americanus) in Narragansett Bay, Rhode Island     

Bridget A. Holohan  Eric G. Klos  Candace A. Oviatt 《Estuaries and Coasts》1998,21(3):466-469

The maximum population density of the burrowing anemone (Ceriantheopsis americanus) was estimated at 17–28 animals m^?2 in soft-bottom sediments of mid Narragansett Bay. The gut contents of the anemone indicated primary prey of harpacticoid and calanoid copepods. The consumption of calanoid copepods was higher in October than April, which may be due to decreased density of hapacticoids in the fall. The anemones apparently avoid fish predation in late summer by withdrawing into the sediments. After the seasonal fall migration of fish out of the bay, anemones reappear.  相似文献   

Isotope and trace element geochemistry of sediments from the Barbados Ridge-Demerara Plain region,Atlantic Ocean     

William M. White  Bernard Dupré  Philippe Vidal 《Geochimica et cosmochimica acta》1985,49(9):1875-1886

Twenty-four piston core sediment samples and 13 sediments and 3 basalts from DSDP Leg 78 Site 543 were analyzed for Sr, Nd and Pb isotopic compositions. The results show sediment with highly radiogenic Pb${}^{206}\text{Pb}{}^{204}\text{Pb}$ up to 19.8) and rather radiogenic Sr and unradiogenic Nd has been deposited in the region since the Cretaceous. The source of this sediment is probably the Archean Guiana Highland, which is drained by the Orinoco River. Pb and Sr isotopic compositions and sediment thickness decrease and${}^{143}\text{Nd}{}^{144}\text{Nd}$ increases northward due to a decrease in turbiditic component. This decrease is partly due to the damming action of basement ridges. Rare earth concentrations in the sediments are somewhat low, due to the abundance of detrital and biogenic components in the sediment and rapid sedimentation rates. Both positive and negative Ce anomalies occur in the surface sediments, but only positive Ce anomalies occur in the Site 543 sediments. It is unlikely that sediment subducted to the source region of Lesser Antilles arc magmas could be the cause of negative Ce anomalies in those magmas.Isotopic compositions of Site 543 basalts show some effect of contamination by seawater-basalt reaction products and sediments. Beyond this, however, they are typical of “normal” depleted MORB.  相似文献   

U-238 series radioactive disequilibrium in groundwaters: implications to the origin of excess U-234 and fate of reactive pollutants     

N. Hussain  S. Krishnaswami 《Geochimica et cosmochimica acta》1980,44(9):1287-1291

The concentrations of ²³⁸U, ²³⁴Th, ²²⁶Ra, ²²²Rn and ²¹⁰Pb and ${}^{234}\text{U}{}^{238}\text{U}$ activity ratios have been measured in several groundwater samples from Gujarat, India. In the aqueous phase the abundances of ²³⁴Th and ²¹⁰Pb are grossly deficient relative to their parents, ²³⁸U and ²²²Rn respectively. The deficiency is ascribable to the impact adsorption of ²³⁴Th and ²¹⁰Pb atoms onto particle surfaces which are very abundant in the groundwater regimes. The scavenging residence times for both these nuclides is about a day, suggesting that irreversible removal of ‘reactive’ metals and pollutants in groundwaters can occur on very short time scales. The fast removal of ²³⁴Th onto particles necessitates that in these groundwaters ²³⁴U ‘excess’ has to originate through leaching of soil grains rather than through in situ decay of dissolved ²³⁴Th in the water.  相似文献