THORIUM and DISEQUILIBRIA

THORIUM DISEQUILIBRIA

1 of 12

TI: Scavenging and particle residence times determined from super(234)Th/ super(238)U disequilibria in the coastal waters of Mecklenburg Bay

AU: Kersten,-M.; Thomsen,-S.; Priebsch,-W.; Garbe-Schoenberg,-C.-D.

AF: Marine Geology Section, Institut fuer Ostseeforschung Warnemuende, Seestr. 15, 18119 Rostock, Germany

SO: Appl.-Geochem. 1998 vol. 13, no. 3, pp. 339-347

LA: English

AB: Activities of the naturally occurring radionuclide super(234)Th were determined in water samples of Mecklenburg Bay (SW Baltic Sea) using a new Th-specific diatomite adsorption technique followed by liquid scintillation spectrometry. Activities of "dissolved" (operationally defined as Th in the centrifugate) and particulate super(234)Th varied in the range of 1.4-6.9 and 0.9-9.3 mBq l super(-1), respectively. A significant correlation between K sub(d) and SPM concentration was found. From this particle-concentration effect, the "colloidal pumping" model predicts that 98% of the "dissolved" Th is associated with colloids rather than being truly dissolved. Relative to calculated activities of the parent nuclide super(238)U in the Bay, the super(234)Th data yielded mean super(234)Th scavenging residence times in the range of 1.2-9.7 days. Particulate super(234)Th activities are inversely correlated to SPM concentrations. Particle residence times ranged from a few days in winter up to 20 days in spring characterized by less intense bottom currents. The hydrodynamic regime is the master variable controlling scavenging of Th and other similarly particle-reactive elements in Mecklenburg Bay.

AN: 4348103

2 of 12

TI: Melting of a subducting oceanic crust from U-Th disequilibria in austral Andean lavas

AU: Sigmarsson,-O.; Martin,-H.; Knowles,-J.

AF: Cent. Natl. Rech. Sci. (CNRS) and Univ. Blaise Pascal, 5 rue Kessler, 63038 Clermont-Ferrand, France

SO: Nature 1998 vol. 394, no. 6693, pp. 566-569

LA: English

ER: M (Marine)

AB: Understanding crustal genesis at convergent plate boundaries is important for determining mass transfer between different geochemical reservoirs in the Earth's mantle, and for deciphering the long-term growth of the continental crust. Most arc magmas are thought to be generated from fluid-induced melting of the mantle wedge above slabs of subducting oceanic crust. Such magmas frequently display super(238)U enrichments or radioactive equilibrium between super(238)U and its radiogenic product super(230)Th. But where a young and hot oceanic crust is being subducted it may itself partially melt and produce calc-alkaline andesites and dacites, termed adakites. Here we report a uniform excess of super(230)Th over super(238)U, but variable Th isotope ratios, in young adakites from the Andean austral volcanic zone south of the triple junction where the Chile ridge subducts beneath South America. We show that these results are compatible with the adakites having been formed by approximately 20% equilibrium melting due to amphibole decomposition in a heterogeneous oceanic crust. Moreover, both the degree of melting of the oceanic crust and its thermal structural appear to be uniform under most of the Andean austral volcanic zone. Such partial melting of subducted oceanic slabs may have occurred throughout the Earth's history where young oceanic plates were subducted.

AN: 4352674

3 of 12

TI: Radioactivity levels in the Red Sea coastal environment of Sudan

AU: Sam,-A.K.; Ahamed,-M.M.O.; El-Khangi,-F.A.; El-Nigumi,-Y.O.; Holm,-E.

AF: Department of Radiation Physics, Lund University, Sweden

SO: Mar.-Pollut.-Bull. 1998 vol. 36, no. 1, pp. 19-26

LA: English

ER: M (Marine)

AB: Measurements of natural and fallout radionuclides in marine surface sediments, seagrass and algae collected from the Sudanese coastal waters of the Red Sea have been made using high resolution gamma -spectrometry, radiochemical separation and alpha -spectrometry. Activity levels of uranium isotopes, thorium isotopes, super(226)Ra, super(210)Po, super(40)K and super(137)Cs were determined in the samples. Comparison of the data on natural radionuclides from coastal marine sediments with those collected from 30 km offshore (Sanganeb atoll) reveals that both anthropogenic and terrestrial influx from the hinterland is negligible. However, values for super(226)Ra and super(210)Po are higher in the sediments of Port Sudan harbour relative to those from the adjacent fringing reefs. Uranium content is higher in shallow-water sediments and the authigenic fraction constitutes 12% on the average. The super(228)Th: super(232)Th disequilibrium in sediments indicates rapid rate of sedimentation at the sampling sites. The activity levels detected for super(137)Cs in sediments collected from the Port Sudan harbour area are fairly high as compared with values from other sampling locations. On the basis of individual data, the variations are insignificant with regard to the uptake of natural radionuclides by marine species considered in this study. However, super(137)Cs activity in algae ranged from 0.33 to 1.32 Bq kg super(-1) with Sargassum (brown algae) showing the highest level.

AN: 4326540

4 of 12

TI: Particle dynamics in the euphotic zone. 6. The utility of tracer super(234)Th for studying particle dynamics in the upper water column of the northeastern South China Sea

AU: Chen,-Min; Huang,-Yipu; Chen,-Feizhou; Qiu,-Yusheng; Xu,-Maoquan; Jiang,-Desheng

AF: Dep. Oceanogr., Xiamen Univ., Xiamen 361005, People's Rep. China

SO: Trop.-Oceanol.-Redai-Haiyang 1997 vol. 16, no. 2, pp. 91-103

LA: Chinese

ER: M (Marine)

AB: The disequilibrium between the particle-reactive tracer super(234)Th (T sub(1/2)=24.1d) and its soluble parent, super(238)U, was used to study the particle dynamics at three stations in the northeastern South China Sea. Profiles of dissolved and particulate super(234)Th in the upper 500m and a steady state box model were used to quantify dissolved super(234)Th scavenging and particle removal rates. Some valuable biogeochemical information have been gained by combination with the profiles of nutrients (NO sub(3) super(-), NO sub(2) super(-), SiO sub(3) super(2-), PO sub(4) super(3-)), S, T, DO, TSM and POC. The calculated parameters suggested that three stations have two kinds of thorium structure in the euphotic zone, which is consistent with the conclusion we obtained in the Nansha sea area. The POC export fluxes out of the euphotic zone were 4.0, 25.0 and 5.4 mol scalar product of C and m super(-2) and d super(-1) respectively. The relations between the residence times of POC and PTh have also been discussed.

AN: 4313363

5 of 12

TI: Settling removal rates of PCBs into the northwestern Atlantic derived from super(238)U- super(234)Th disequilibria

AU: Gustafsson,-Oe.; Gschwend,-P.M.; Buesseler,-K.O.

AF: Swedish Mus. Nat. History, Div. Isotope Geol., Box 50007, 10405 Stockholm, Sweden

SO: ENVIRON.-SCI.-TECHNOL. 1997 vol. 31, no. 12, pp. 3544-3550

LA: English

ER: M (Marine)

AB: Surface ocean export fluxes of polychlorinated biphenyls (PCBs) were deduced utilizing super(234)Th as an indicator of the removal rates of particle-bound species from coastal, continental shelf, and pelagic surface waters. The fraction of the PCB settling flux that reaches the sediments (the ratio of bottom sediment import flux to super(234)Th-derived surface ocean export flux) decreased with both water column depth and with aqueous solubility of the congeners, presumably as a result of particle decomposition and/or compound desorption. A sharper decrease in super(234)Th-derived surface ocean fluxes away from the continental source was seen for congeners with increasing chlorination. This suggests that atmospheric washout followed by particle-mediated settling out of the surface ocean are the predominant processes affecting the PCBs, as opposed to atmospheric hydroxyl radical-mediated decomposition. Based on this limited data set, the largest fraction of each PCB is removed into the open ocean, although higher areal fluxes are seen closer to the coast. For example, we estimate that 14 000 mol yr super(-1) of a tetrachlorobiphenyl (congener 52) were sequestered in the northwestern Atlantic Ocean in 19931994, with 75% of the flux being in the pelagic sector, 20% on the continental shelf, and only 5% in the 20-km-wide coastal region closest to the continental source.

AN: 4254685

6 of 12

TI: super(238)U- super(230)Th disequilibria, magma petrogenesis, and flux rates beneath the depleted Tonga-Kermadec island arc

AU: Turner,-S.; Hawkesworth,-C.; Rogers,-N.; Bartlett,-J.; Worthington,-T.; Hergt,-J.; Pearce,-J.; Smith,-I.

AF: Dep. Earth Sci., Open Univ., Milton, Keynes MK7 6AA, UK

SO: GEOCHIM.-COSMOCHIM.-ACTA 1997 vol. 61, no. 22, pp. 4855-4884

LA: English

ER: M (Marine)

AB: The highly depleted intra-oceanic Tonga-Kermadec island arc forms an endmember of arc systems and a unique location in which to isolate the effects of the slab flux. High precision TIMS uranium, thorium, strontium, neodymium, and lead isotopes, along with complete major and trace element data, have been obtained on an extensive sample set comprising fifty-eight lavas along the arc as well as nineteen samples of the subducting sediments at DSDP site 204 just to the east of the Tonga-Kermadec trench. Ca/Ti and Al/Ti ratios extend from values appropriate to an N-MORB source in the southern Kermadecs to very high ratios in Tonga interpreted to reflect increasing degrees of depletion of the mantle wedge due to backarc basalt extraction.

AN: 4273963

7 of 12

TI: super(238)U- super(234)U- super(230)Th disequilibrium in hydrogenous oceanic Fe-Mn crusts: Palaeoceanographic record or diagenetic alteration?

AU: Chabaux,-F.; O'-Nions,-R.K.; Cohen,-A.S.; Hein,-J.R.

AF: Cent. de Geochimie de la Surface, CNRS, 67084 Strasbourg Cedex, France

SO: GEOCHIM.-COSMOCHIM.-ACTA 1997 vol. 61, no. 17, pp. 3619-3632

LA: English

ER: M (Marine)

AB: A detailed TIMS study of ( super(234)U sub(exc)/ super(238)U), ( super(230)Th / super(232)Th), and Th/U ratios have been performed on the outermost margin of ten hydrogenous Fe-Mn crusts from the equatorial Pacific Ocean and west-central Indian Ocean. Th/U concentration ratios generally decrease from the crust's surface down to 0.5-1 mm depth and growth rates estimated by uranium and thorium isotope ratios are significantly different in Fe-Mn crusts from the Peru Basin and the west-central Indian Ocean. Fe-Mn crusts from the same geographical area define a single trend in plots of Ln( super(234)U sub(exc)/ super(238)U) vs. Ln( super(230)Th/ super(232)Th) and Th/U ratios vs. age of the analysed fractions. Results suggest that (1) hydrogenous Fe-Mn crusts remain closed-systems after formation, and consequently (2) the discrepancy observed between the super(230)Th and super(234)U chronometers in Fe-Mn crusts, and the variations of the Th /U ratios through the margin of Fe-Mn crusts, are not due to redistribution of uranium and thorium isotopes after oxyhydroxide precipitation, but rather to temporal variations of both Th/U and initial thorium activity ratios recorded by the Fe-Mn layers. Implications of these observations for determination of Fe-Mn crust growth-rates are discussed. Variations of both Th/U and initial Th activity ratios in Fe-Mn crusts might be related to changes in particle input to seawater and/or changes in ocean circulation during the last 150 ka.

AN: 4248916

8 of 12

TI: Radioactive disequilibrium of uranium and thorium nuclide series in river waters from the Ta-Tun volcanic group area in Taiwan

AU: Chu,-Tieh-Chi; Wang,-Jeng-Jong

AF: Dep. Nuclear Sci., Natl. Tsing Hua Univ., Hsinchu, Taiwan 300

SO: APPL.-RADIAT.-ISOT. 1997 vol. 48, no. 8, pp. 1149-1155

LA: English

ER: F (Freshwater)

AB: Alpha spectrometry and liquid scintillation counting were used in this study to analyze the radioactivities of the naturally occurring radionuclides, super(238)U, super(234)U, super(232)Th, super(230)Th, super(228)Th and super(226)Ra, in the river waters from the Ta-Tun volcanic group area in Northern Taiwan. The respective concentration range of super(238)U, super(234)U, super(232)Th, super(230)Th, super(228)Th and super(226)Ra was 0.80-48, 1.2-51, 0.05-44, 0.09-39, 0.19-342 and 3.0-22.5 mBq L super(-1) and the super(234)U/ super(238)U and super(228)Th/ super(232)Th activity ratios were greater than 1, indicating radioactive disequilibrium in the waters. The high super(228)Th/ super(232)Th activity ratios showed that besides the recoil effect, enrichment of super(228)Ra to super(232)Th in the waters was another possible factor causing an excess of super(228)Th. The concentrations of uranium and thorium in the river waters changed with the pH of the water. The U/Th concentration ratio was about 1; in the acidic (pH < 5) samples; whereas it was much higher than 1 in neutral (pH similar to 7) samples.

AN: 4239788

9 of 12

TI: Using super(234)Th disequilibria to estimate the vertical removal rates of polycyclic aromatic hydrocarbons from the surface ocean

AU: Gustafsson,-O.; Gschwend,-P.M.; Buesseler,-K.O.

AF: Department of Civil and Environmental Engineering, MIT 48-415, Massachusetts Institute of Technology, Cambridge, MA 02139, USA

SO: MAR.-CHEM. 1997 vol. 57, no. 1-2, pp. 11-23

LA: English

AB: A novel 234Th-coupled approach was employed to deduce the vertical fluxes of polycyclic aromatic hydrocarbons (PAHs) through surface waters of harbor, coastal, shelf, and pelagic regimes. We found reasonable agreement between these surface ocean fluxes, based on direct measurements of mixed-layer properties, and fluxes deduced from underlying sediments. Fluxes decreased exponentially away from the northeastern U.S.A. Source-diagnostic molecular ratios indicate that atmospheric fall-out of combustion-derived PAHs from the continents is the dominant source. Despite higher unit area fluxes inshore, the open ocean represents a large integral sink for PAHs. For example, of the 60 metric tonnes of pyrene that we estimate to annually become sequestered in the western North Atlantic, only similar to 10% is deposited in coastal waters while the remaining 90% is exported farther offshore on the continental shelf and to pelagic regimes.

AN: 4070875

10 of 12

TI: super(234)Th scavenging and particle export fluxes from the upper 100 m of the Arabian Sea

AU: Sarin,-M.M.; Rengarajan,-R.; Ramaswamy,-V.

AF: Physical Research Laboratory, Ahmedabad 380 009, India

SO: CURR.-SCI. 1996 vol. 71, no. 11, pp. 888-893

LA: English

ER: M (Marine)

AB: We have determined the particle scavenging rates, export fluxes of super(234)Th and settling particles from the upper 100 m of the Arabian Sea as a part of the JGOFS (India) Programme. The spatial and temporal measurements made in the open ocean profiles reveal close similarities in the dissolved super(234)Th: super(238)U disequilibria, suggesting that the rates of particle-associated scavenging processes are generally uniform in the central Arabian Sea. The observed disequilibrium integrated for the upper 100 m yields a mean scavenging residence time of mu 30 days and a removal rate of mu 3400 dpm m super(-2) d super(-1) for super(234)Th, from dissolved to particulate phases. The deficiency of total super(234)Th (dissolved + particulate) relative to super(238)U allows us to compute the vertical export flux of particulate super(234)Th. The flux data for the upper 100 m show spatial variations with enhanced export fluxes centered around 22 degree N 67 degree E, a region characterized by higher rates of column primary productivity. Using the super(234)Th export fluxes and the measured specific activity of super(234)Th in the sediment traps, we have computed th eparticle and carbon fluxes at 100 m. These results reveal that the particle fluxes determined from sediment traps are systematically low and the estimated C export fluxes are grossly out of proportion with the column primary production.

AN: 4034487

11 of 12

TI: Particle dynamics in euphotic zone 4. The regional estimates of the export pdoduction derived from super(234)Th/ super(238)U disequilibria in the Nansha sea area

AU: Chen,-Min; Huang,-Yipu; Chen,-Feizhou; Qiu,-Yusheng; Xie,-Yongzhen; Chen,-Xingbao; Cai,-Pinghe

AF: Dep. Oceanogr., Xiamen Univ., Xiamen 361005, People's Rep. China

CA: The Multidisciplinary Oceanogr. Exped. Team of Acad. Sin. to Nansha I., (China)

SO: ISOTOPE-MARINE-CHEMISTRY-OF-NANSHA-ISLANDS-WATERS.-NANSHAQUNDAO-HAIYU-DE-TONGWEISU-HAIYANGHUAXUE BEIJING-CHINA CHINA-OCEAN-PRESS 1996 pp. 145-153

LA: Chinese

ER: M (Marine)

AB: We have measured the profiles of super(234)Th/ super(238)u) sub(A.R.) and the POC/PTh ratios in the Nansha sea area, so we can estimate the export production (new production)by using two different approaches. The estimated export production within this region in the autumn and in the winter ranges from 2.9-28.7mmol/(m super(2).d) and 3.8-32.4mmol/(m super(2).d), respectively. The results derived from two different approaches agree to within 30%, which shows the super(234)Th is a very accurate tracer for carbon cycle. The effect of advection and diffusion on the calculation of super(234)Th fluxes has also been discussed.

AN: 3983292

12 of 12

TI: Particle dynamics in euphotic zone 3. The stratified structure and export production in the euphotic zone of the Nansha sea area

AU: Huang,-Yipu; Chen,-Min; Chen,-Feizhou; Qiu,-Yusheng; Xie,-Yongzhen; Huang,-Liangmin; Chen,-Shaoyong; Wang,-Hankui

AF: Dep. Oceanogr., Xiamen Univ., Xiamen 361005, People's Rep. China

CA: The Multidisciplinary Oceanogr. Exped. Team of Acad. Sin. to Nansha I., (China)

SO: ISOTOPE-MARINE-CHEMISTRY-OF-NANSHA-ISLANDS-WATERS.-NANSHAQUNDAO-HAIYU-DE-TONGWEISU-HAIYANGHUAXUE BEIJING-CHINA CHINA-OCEAN-PRESS 1996 pp. 134-144

LA: Chinese

ER: M (Marine)

AB: The application of super(234)Th/ super(238)U disequilibrium to study the particle dynamics in the euphotic zone of the Nansha sea area during the 1993 winter cruise had been made. The activities of dissolved and particulate super(234)Th in water column were determined and treated by boxmodel with ateady state assumption. The calculated results showed that the residence times of dissolved and particulate super(234)Th were in the ranges of 84-125 days and 16- 96 days, respectively. The difference of scavenging fluxes(J),removal fluxes (F) and residence times between the mixed layer and the lower euphotic zone suggested that the studied station have the stratified two-layer euphotic structure, which is further confirmed by the POC export fluxes out of different boxes. The POC export flux out of euphotic zone (export production) was 19.3mmol/(m super(2).d). The ways of nutrients transported into euphotic zone for supporting this export production was discussed. The covariance of the residence times of particulate super(234)Th and POC showed that super(234)Th is an excellent tracer for POC cycle.

AN: 3983291

No. Records Request

1: 60 THORIUM

2: >54 DISEQUILIBRI*

3: 12 THORIUM and DISEQUILIBRI*

Searches and records above from: ASFA 1997-1998/09

5: 25 #3

1 of 25

TI: Constraints on mantle melting at mid-ocean ridges from global super(238)U- super(230)Th disequilibrium data

AU: Bourdon,-B.; Zindler,-A.; Elliott,-T.; Langmuir,-C.H.

AF: Lab. Geochim. et Cosmochim., CNRS, IPGP 4, Place Jussieu 75252 Paris, Cedex 05, France

SO: NATURE 1996 vol. 384, no. 6606, pp. 231-235

LA: English

ER: M (Marine)

AB: The extent of radioactive disequilibrium between super(238)U and its daughter product super(230)Th in mid-ocean-ridge basalts from around the world is negatively correlated with axial ridge depth; local positive correlations with inferred mantle source composition are also observed. The larger super(230)Th excesses seen in samples from shallow ridges reflect a larger melt contribution from a garnet-bearing source which may be explained by a deepening of the solidus in hotter mantle regions. These observations provide important constraints for modelling melt generation at mid-ocean ridges.

AN: 3970073

2 of 25

TI: Ridge-hotspot interaction along the Mid-Atlantic Ridge between 37 degree 30' and 40 degree 30'N: The U-Th disequilibrium evidence

AU: Bourdon,-B.; Langmuir,-C.H.; Zindler,-A.

AF: Lab. de Geochimie et Cosmochimie, CNRS, IPGP T14-24, 4 Place Jussieu, 75252 Paris Cedex 05, France

SO: EARTH-PLANET.-SCI.-LETT. 1996 vol. 142, no. 1-2, pp. 175-189

LA: English

ER: M (Marine)

AB: This study reports U-Th disequilibrium data obtained by mass spectrometry for basaltic glasses collected along the Azores platform portion of the Mid-Atlantic Ridge (37 degree 30'-40 degree 30'N), a region characterized by both a geochemical and bathymetric gradient. High Th and U concentrations, as well as Th/U ratios, document an enriched geochemical signature. ( super(230)Th/ super(238)U) activity ratios range from 1.20 to 1.35 and are thus systematically larger than most EPR MORBs reported in the literature. ( super(230)Th/ super(232)Th) activity ratios show remarkable homogeneity for multiple samples taken from single dredge hauls. Additionally, samples with the highest Th concentrations (2.4 ppm) have among the highest Th isotope ratios. Taken together, these observations rule out assimilation of super(230)Th-rich sediment as an explanation for the super(230)Th- super(238)U systematics. The relatively large super(230)Th excesses in the erupted lavas may be related to the influence of the enriched Azores mantle plume source. The lack of observed correlations between super(230)Th excess and trace element and isotopic indices of source enrichment, however, rules out source composition as an explanation for the variations in ( super(230)Th/ super(238)U).

AN: 3963951

3 of 25

TI: Natural U-Th series radionuclide studies of estuarine processes

AU: Church,-T.M.; Sarin,-M.M.

AF: Robinson Hall, Univ. Delaware, Newark, DE 19716-3501, USA

CO: ECSA22/ERF Symposium, Plymouth (UK), 13-18 Sep 1992

SO: CHANGES-IN-FLUXES-IN-ESTUARIES:-IMPLICATIONS-FROM-SCIENCE-TO-MANAGEMENT. Dyer,-K.R.;Orth,-R.J.-eds. FREDENSBORG,-DENMARK OLSEN-and-OLSEN 1994 pp. 91-95

LA: English

ER: B (Brackish)

AB: The natural uranium and thorium decay series provides a series of elements, the chemistry and decay times of which reveal key estuarine processes. In turn, estuarine processes impose disequilibria on the series which can define the rates of many estuarine processes. Radionuclide studies have been conducted in the Delaware Estuary and its pervasive salt marshes over the past 10 years. In the Delaware Estuary, uranium shows conservative behavior, except in the upper reaches during the summer season. Both in the estuary and in the surrounding salt marsh sediments, important uranium uptake processes occur concurrent with a minimum in alkalinity and maximum in phosphate. This suggests that iron/phosphate based scavenging processes out-compete the carbonate-complexes which normally stabilize uranium in estuarine and sea waters. Such uptake of uranium in th world's estuaries could constitute a significant global sink for marine uranium. Thorium and lead in the Delaware Estuary show dominant particle association. During periods of high productivity, the super(210)Pb granddaughter, super(210)Po, seasonally shows dissolved activity excesses, particularly in tidal waters of salt marshes. The polonium excesses persist out onto shelf areas as the lead parent is removed by particulate sedimentation processes. The polonium excesses are believed to be associated with coastal processes of organic association and complexation.

AN: 3883514

4 of 25

TI: Natural radionuclide and plutonium content in Black Sea bottom sediments

AU: Strezov,-A.; Yordanova,-I.; Pimpl,-M.; Stoilova,-T.

AF: Inst. for Nuclear Res. and Nuclear Energy, Boul. Tzarigradsko Chaussee 72, Sofia 1784, Bulgaria

SO: HEALTH-PHYS. 1996 vol. 70, no. 1, pp. 70-80

LA: English

ER: M (Marine)

AB: The content of uranium, thorium, radium, lead, polonium, and plutonium in bottom sediments and algae from two locations at the Bulgarian Black Sea coast have been determined. Some parent: progeny ratios for evaluation of the geochemical behavior of the nuclides have been estimated as well. The extractable and total uranium and thorium are determined by two separate radiochemical procedures to differentiate the more soluble chemical forms of the elements and to estimate the potential hazard for the biosphere and for humans. No distinct seasonal variation as well as no significant change in total and extractable uranium (also for super(226)Ra) content is observed. The same is valid for extractable thorium while the total thorium content in the first two seasons is slightly higher. Our data show that super(210)Po content is accumulated more in the sediments than super(210)Pb, and the evaluated disequilibria suggest that the two radionuclides belong to more recent sediment layers deposited in the slime samples compared to the silt ones for the different seasons. The obtained values for plutonium are in the lower limits of the data cited in literature, which is quite clear as there are no plutonium discharge facilities at the Bulgarian Black Sea coast. The obtained values for the activity ratio super(238)Pu: super(239+240)Pu are higher for Bjala sediments compared to those of Kaliakra. The ratio values are out of the variation range for the global contamination with weapon tests fallout plutonium which is probably due to Chernobyl accident contribution. The dependence of natural radionuclide content on the sediment type as well as the variation of nuclide accumulation for two types of algae in two sampling locations for five consecutive seasons is evaluated. No serious contamination with natural radionuclides in the algae is observed.

AN: 3878387

5 of 25

TI: Role of colloids in upper ocean biogeochemistry in the Northeast Pacific Ocean elucidated from super(238)U- super(234)Th disequilibria

AU: Huh,-Chih-An; Prahl,-F.G.

AF: Coll. Ocean. Atmos. Sci., Oregon State Univ., Corvallis, OR 97331-5503, USA

SO: LIMNOL.-OCEANOGR. 1995 vol. 40, no. 3, pp. 528-532

LA: English

ER: M (Marine)

AB: Detailed upper ocean profiles of super(234)Th in dissolved (<10,000 Daltons), colloidal (10,000 Da-0.45 mu m), and particulate (>0.45 mu m) forms were measured at a station (46 degree 45'N, 126 degree W) in the northeast Pacific Ocean. On average, dissolved, colloidal, and particulate super(234)Th accounted for similar to 78, 12, and 10% of the total super(234)Th in the euphotic zone (0-100 m). A highly positive correlation exists between colloidal super(234)Th and chlorophyll a; both are characterized by higher concentrations in surface waters, a subsurface maximum at 55 m in the seasonal thermocline, and undetectable levels below the euphotic zone. POC:CH1 a ratios in the water column suggest phytoplankton as primary producers of the colloidal material. Scavenging residence times of dissolved, colloidal, and particulate super(234)Th with respect to their removal processes in the euphotic zone are similar to 50, 6, and 8 d. The scavenging rate constant of Th apparently increases with the concentration of colloids.

AN: 3843218

6 of 25

TI: Stratigraphy, sedimentology, chronology and palaeohydrology of Quaternary lacustrine deposits at Madigan Gulf, Lake Eyre, South Australia

AU: Magee,-J.W.; Bowler,-J.M.; Miller,-G.H.; Williams,-D.L.G.

AF: Div. Archaeol. Nat. His., R.S.P.A.S., Australian Natl. Univ., Canberra, A.C.T. 0200, Australia

SO: PALAEOGEOGR.,-PALAEOCLIMATOL.,-PALAEOECOL. 1995 vol. 113, no. 1, pp. 3-42

LA: English

ER: F (Freshwater)

AB: Madigan Gulf is a large bay at the southern end of Lake Eyre North, a major ephemerally flooded playa in arid central Australia at the southwestern margin of a vast (1,300,000 km super(2)) internal drainage basin. The stratigraphy and chronology of the Quaternary sequence in the gulf is described from 8 cores and a cliff exposure at the gulf margin. A number of depositional environments are recognised and their distinctive sedimentary components are described. Facies recognised include deep- and shallow-water lacustrine environments, dominated by surface-water processes, and dry or ephemerally flooded playa environments dominated by groundwater-controlled processes. Sedimentary components include terrigenous clastics from river inflow and shoreline erosion, carbonates of detrital, inorganic or biological origin and gypsum and halite evaporites. Carbonates and gypsum evaporites, precipitated within the basin, are frequently reworked as clastic components. The establishment of a preliminary chronology for the sequence, by the application of thermoluminescence, uranium/thorium disequilibrium, amino acid racemization and radiocarbon dating techniques, has allowed a reconstruction of the last 130 ka of Lake Eyre palaeohydrology. The wettest phase occurred during the last interglacial (early in oxygen isotope stage 5) when an enlarged Lake Eyre was up to 25 m deep. Subsequently there has been a number of dry periods separating successively less effective wet phases culminating in the deposition of a substantial halite salt crust around the time of the glacial maximum. The dry interludes are characterized by deflation of salts and sediment from the basin, a process controlled by lowering of the watertable. The record from Madigan Gulf demonstrates the dramatic and repetitive impact of lake deflation on the Quaternary record of Lake Eyre. In the early Holocene a minor, but mostly perennial, lacustrine event was terminated at about 3-4 ka when the modern ephemeral playa regime was established. The major catchment of Lake Eyre is located in the monsoon-watered areas of northern Australia. As demonstrated by large floodings of the modern ephemeral regime, major lacustrine episodes must indicate enhanced monsoon precipitation in northern Australia. In the Holocene the lake has not risen to levels achieved during the early stage 5 lacustral phase, indicating a marked reduction in the effectiveness of the monsoon in the present interglacial by comparison with its predecessor.

AN: 3836987

7 of 25

TI: Tracing, particle cycling in the upper ocean with super(230)Th and super(228)Th: An investigation in the Equatorial Pacific along 140 degree W

AU: Luo,-Shangde; Ku,-Teh-Lung; Kusakabe,-M.; Bishop,-J.K.B.; Yang,-Yong-Liang

AF: Dep. Earth Sci., Univ. Southern California, Los Angeles, CA 90089-0740, USA

SO: DEEP-SEA-RES.-II-TOP.-STUD.-OCEANOGR. 1995 vol. 42, no. 2-3, pp. 805-829

LA: English

ER: M (Marine)

AB: Vertical distributions of super(230)Th and super(228)Th were measured in large-volume (2000 to 3000 liter) seawater samples collected with the Multiple Unit In-Situ Large-Volume Filtration System (MULVFS) and in-situ Fe/Mn-fiber enrichment technique. The samples were from the upper similar to 800 m of the water column in the Central Equatorial Pacific along similar to 140 degree W during two survey cruises of JGOFS EqPac in February/March (Survey I) and August/September (Survey II) 1992. Significantly lower activities of super(230)Th and super(228)Th relative to those of their parent isotopes exist in the upper-ocean water column due to their particle-reactive behavior. The activities of these thorium isotopes also show large temporal variations, in response to surface productivity changes. During Survey I, a period of the El Nino, the super(230)Th and super(228)Th activities were higher than those measured during Survey II (a non-El Nino period), reflecting a depressed ocean productivity and particle flux under El Nino conditions. Vertical profiles of super(230)Th show a minimum at about 50 to 100 m, suggesting maximal particle scavenging in this depth range. Below this depth interval is a super(230)Th chemocline (rapid increase in super(230)Th activities with depth) and a super(228)Th activity maximum. The occurrence of the super(230)Th chemocline and the super(228)Th maximum just below the euphotic zone is a manifestation of active particle regeneration. Based on the extent of radioactive disequilibria between super(228)Th and super(228)Ra and between super(230)Th and super(234)U, we have estimated vertical fluxes of the two Th isotopes and of the particle mass. The export particle flux reaches a maximum in the lower portion of the euphotic zone, followed by a rapid decrease resulting from intensive particle remineralization in the super(230)Th chemocline/ super(228)Th maximum region. The scavenging rates of super(228)Th and super(230)Th are not balanced by their in-situ production and radioactive decay. The imbalance is attributable to their diffusional and advective transport. From the vertical profiles of particle fluxes derived from super(228)Th and super(230)Th, export fluxes of particulate organic carbon (POC) at the base of the euphotic zone are estimated to be 0.6-1.3 mmol C m super(-2)day super(-1) during El Nino, and 1.5-5.0 mmol C m super(-2)day super(-1) during the non-El Nino period. These values are small compared to the new production, indicating that much of the organic matter must be removed from the euphotic zone in dissolved form. Deeper at similar to 800 m, the POC fluxes are reduced to 0.14-0.50 mmol C m super(-2)day super(-1) (El Nino) and 0.5-1.1 mmol C m super(-2)day super(-1) (non-El Nino).

AN: 3822076

8 of 25

TI: Oceanic stratified euphotic zone as elucidated by super(234)Th: super(238)U disequilibria

AU: Coale,-K.H.; Bruland,-K.W.

AF: Inst. Mar. Sci., Univ. California, Santa Cruz, CA 95064, USA

SO: LIMNOL.-OCEANOGR. 1987 vol. 32, no. 1, pp. 189-200

LA: English

ER: M (Marine)

AB: Profiles of dissolved and particulate super(234)Th were determined at the VERTEX 2 and 3 stations off Manzanillo, Mexico, and at the VERTEX 4 station about 900 km north of Hawaii. By modeling the disequilibria between super(234)Th and super(238)U in the dissolved and particulate form, estimates of scavenging rates for Th from the dissolved to particulate phases, particle residence times, and the flux of Th via particle removal can be obtained. super(234)Th: super(238)U activity ratio profiles indicate that the euphotic zone can be separated into two layers: An upper oligotrophic layer characterized by low new production values, low net scavenging, and long dissolved super(234)Th residence times; and a subsurface eutrophic layer with higher new production values, more intense scavenging, and shorter dissolved super(234)Th residence times. New production, rather than total primary production may determine net scavenging rates of reactive elements from oceanic surface waters. These results contribute to the emerging descriptions of the layered structure of oligotrophic euphotic zones and support the notion that this may be a general and ubiquitous feature of global stratified oligotrophic regimes. These layered systems can be structured not only in biological and nutrient parameters, but also in terms of the rates of chemical scavenging and elemental transport. (DBO)

AN: 3652008

9 of 25

TI: super(231)Pa and super(230)Th chronology of mid-ocean ridge basalts

AU: Goldstein,-S.J.; Murrell,-M.T.; Williams,-R.W.

AF: Los Alamos Natl. Lab., MS K484 Los Alamos, NM 87545, USA

SO: EARTH-PLANET.-SCI.-LETT. 1993 vol. 115, no. 1-4, pp. 151-159

LA: English

ER: M (Marine)

AB: Mass spectrometric measurements of super(235)U- super(231)Pa and super(238)U- super(230)Th disequilibria are used to further constrain processes producing U-series disequilibria in young mid-ocean ridge basalts (MORB) and to determine eruption ages for samples from 9-10 degree N East Pacific Rise and Juan de Fuca-Gorda ridges. super(231)Pa/ super(235)U activity ratios for axial basalts are large and relatively uniform within ridge segments. The systematically large super(231)Pa/ super(235)U, super(230)Th/ super(238)U, and super(226)Ra/ super(230)Th activity ratios in MORB are inconsistent with simple equilibrium melting models and crustal contamination or seawater alteration processes. More complicated melting processes involving disequilibrium or heterogeneous melting of mantle sources and disequilibrium transport of melts to the crust could produce the large U-series disequilibria in MORB.

AN: 3552974

10 of 25

TI: Bacterial scavenging of super(234)Th in surface ocean waters

AU: Lee,-T.; Barg,-E.; Lal,-D.; Azam,-F.

AF: Scripps Inst. Oceanogr., Geol. Res. Div., La Jolla, CA 92093-0220, USA

SO: MAR.-ECOL.-PROG.-SER. 1993 vol. 96, no. 2, pp. 109-116

LA: English

ER: M (Marine)

AB: super(234)Th was determined in the dissolved (<0.1 mu m), bacterial (0.1 to 1.0 mu m) and 2 larger particulate pools (1 to 5 mu m and > 5 mu m) at 5 or 6 depths in the upper 120 m of the water column at a station (31 degree 51.6'N, 119 degree 31.9' W) in the Southern California Bight during October 1989 and July 1990. Depth profiles of bacterial abundance and chlorophyll a were also measured. The bacterial fraction had high volume concentration factor (VCF: 1 to 4 x 10 super(6)) and the highest estimated super(234)Th/C ratio of all size fractions (5.1 and 5.5 nCi gC super(-1)). The VCF for super(234)Th scavenging by bacteria determined in a microcosm experiment (containing a 2 mu m filtrate of seawater from Scripps pier and spiked with super(234)Th) was on the order of 7 x 10 super(6). Both the bacteria fraction and > 5 mu m fraction had super(234)Th/C ratios comparable to that computed for the colloidal fraction. Sequential transfer of super(234)Th (truly dissolved super(234)Th arrow right disperse colloids arrow right suspended particles arrow right sinking particles) alone does not explain the observed high super(234)Th/C ratio in the bacterial and the large particulate fractions. We propose that the abundant and highly super(234)Th-reactive colloids (which occur bound to the surfaces of free and particle-bound bacteria in addition to their occurrence in the disperse phase) contribute substantially to efficient scavenging of super(234)Th by bacteria as well as colonized particles of all sizes. The contribution by bound colloids may vary with the physiological states of bacteria and phytoplankton and their state of aggregation. This unstructured flow model has implications for models which use super(234)Th/ super(238)U disequilibrium as an indicator for downward flux of particles in the ocean.

AN: 3536848

11 of 25

TI: Application of a generalized scavenging model to time series super(234)Th and particle data obtained during the JGOFS North Atlantic Bloom Experiment

AU: Clegg,-S.L.; Whitfield,-M.

AF: Sch. Environ. Sci., Univ. East Anglia, Norwich NR4 7TJ, UK

SO: DEEP-SEA-RES.-1-OCEANOGR.-RES.-PAP. 1993 vol. 40, no. 8, pp. 1529-1545

LA: English

ER: M (Marine)

AB: Primary production, particle concentration and flux data, obtained as part of the JGOFS North Atlantic Bloom Experiment, have been used to construct a self consistent, time dependent, particle cycle model for the upper water column for the period 25 April-30 May 1989. Daily super(234)Th concentrations and fluxes are modelled over the course of the bloom, and the results compared with available data. Use of a single pseudo-first-order rate constant k sub(1)' for the adsorption of super(234)Th onto particulate material in the model gives satisfactory agreement with measured super(234)Th profiles. Modelled concentrations of super(234)Th on large, sinking particles--which must be known in order to calculate particle fluxes from super(234)Th disequilibrium-are predicted well by the model. The results also suggest that particle fluxes determined from sediment traps may be systematically low.

AN: 3519918

12 of 25

TI: Thorium-uranium fractionation by garnet: Evidence for a deep source and rapid rise of oceanic basalts

AU: LaTourrette,-T.Z.; Kennedy,-A.K.; Wasserburg,-G.J.

AF: Dep. Geol., Box 1404, Arizona State Univ., Tempe, AZ 85287, USA

SO: SCIENCE-WASH. 1993 vol. 261, no. 5122, pp. 739-742

LA: English

ER: M (Marine)

AB: Mid-ocean ridge basalts (MORBs) and ocean island basalts (OIBs) are derived by partial melting of the upper mantle and are marked by systematic excesses of thorium-230 activity relative to the activity of its parent, uranium-238. Experimental measurements of the distribution of thorium and uranium between the melt and solid residue show that, of the major phases in the upper mantle, only garnet will retain uranium over thorium. This sense of fractionation, which is opposite to that caused by clinopyroxene-melt partitioning, is consistent with the thorium-230 excesses observed in young oceanic basalts. Thus, both MORBs and OIBs must begin partial melting in the garnet stability field or below about 70 kilometers. A calculation shows that the thorium-230-uranium-238 disequilibrium in MORBs can be attributed to dynamic partial melting beginning at 80 kilometers with a melt porosity of 0.2 percent or more. This result requires that melting beneath ridges occurs in a wide region and that the magma rises to the surface at a velocity of at least 0.9 meter per year.

AN: 3015908

13 of 25

TI: Carbon and nitrogen export during the JGOFS North Atlantic Bloom Experiment estimated from super(234)Th: super(238)U disequilibria.

AU: Buesseler,-K.O.; Bacon,-M.P.; Cochran,-J.K.; Livingston,-H.D.

AF: Woods Hole Oceanogr. Inst., Woods Hole, MA 02543, USA

SO: DEEP-SEA-RES. 1992. vol. 39, no. 7-8A, pp. 1115-1137

LA: English

ER: M (Marine)

AB: The disequilibrium between the particle-reactive tracer super(234)Th (t sub(1/2) = 24.1 days) and its soluble parent, super(238)U, was used to examine Th scavenging and export fluxes during the U.S. JGOFS North Atlantic Bloom Experiment (24 April-30 May 1989) at similar to 47 degree N, 20 degree W. Four profiles of dissolved and particulate super(234)Th in the upper 300 m and a non-steady state box model were used to quantify dissolved super(234)Th uptake and particle export rates. The highest export fluxes occurred during the first half of May. From POC/ super(234)Th and PON/ super(234)Th ratios, particulate organic C and N fluxes were calculated. Results were 5-41 mmol C m super(2)/day and 0.9-6.5 mmol N m super(-2)/day from the 0-35 m layer. The ratio of POC export flux to primary production ranged from 0.05 to 0.42, peaking in the first half of May. The estimated fluxes agree with the observed losses of total C and N from the upper ocean during the bloom, but yield significantly higher fluxes than were measured by floating traps at 150 and 300 m.

AN: 2866040

14 of 25

TI: Distribution of thorium isotopes in Chinese offshore sediments.

AU: Huang,-Yipu; Shi,-Wenyuan; Lin,-Yongge; Yan,-Xiaoyang

AF: Dep. Oceanogr., Xiamen Univ., Xiamen 361005, People's Rep. China

SO: J.-OCEANOGR.-TAIWAN-STRAIT-TAIWAN-HAIXIA. 1991. vol. 10, no. 4, pp. 302-314

LA: Chinese

ER: M (Marine)

AB: The study of thorium isotopes in the sediments from seven nearshore sea areas of China reveals a homogenous distribution and super(230)Th/ super(232)Th activity < 1.0 in the surficial sediments. However, the values of super(230)Th/ super(232)Th) sub(A.R.) and its depth distribution features in nearshore sediments are totally different from those in deep sea sediments. A well correlation between super(230)Th/ super(232)Th) sub(A.R.) and sampling water depth was established. Thorium series disequilibria characterized by the deficiency of super(228)Th relative to super(232)Th generally exist in the nearshore sediments of China. The depths in sediments to which exchange of soluble chemicals with overlying water occurs are deduced. The content, specific activity of super(232)Th and distribution features of super(232)Th/ super(238)U) sub(C.R.) in sediments are investigated. The surface mixing coefficient of 0.49 x 10 super(-6) cm super(2)/s and the super(234)Th sub(ex.) inventory in the core Xiuyu are estimated.

AN: 2845641

15 of 25

TI: Short residence time of colloids in the upper ocean estimated from super(238)U- super(234)Th disequilibria.

AU: Bradley-Moran,-S.; Buesseler,-K.O.

AF: Woods Hole Oceanogr. Inst., Woods Hole, MA 02543, USA

SO: NATURE. 1992. vol. 359, no. 6392, pp. 221-223

LA: English

ER: M (Marine)

AB: Recent observations of abundant, nonliving, submicrometre particles in the upper ocean and new measurements of "dissolved" organic carbon have fueled speculation concerning the role of colloidal matter in ocean chemistry and biology. Colloids may act as reactive intermediates in the marine geochemistry of trace metals, and a biologically labile pool of colloidal matter would affect models of ocean carbon cycling. Here we report the use of naturally occurring super(234)Th as an in situ tracer to estimate the residence time of colloidal matter in the surface waters near Bermuda. The super(234)Th activity of colloidal matter (size range 10,000 nominal molecular weight to 0.2 mu m) is similar to that of small particles (0.2-53 mu m). Modelling of our results indicates a mean residence time of colloidal super(234)Th with respect to aggregation into small particles of 10 days, which is roughly the same as for small-particle super(234)Th, yet a factor of similar to 6 less than for the dissolved pool. These results suggest that, more generally, macromolecular colloidal matter has a short residence time and hence a rapid turnover rate in the upper open ocean.

AN: 2813084

16 of 25

TI: super(234)U/ super(238)U mass spectrometry of corals: How accurate is the U-Th age of the last interglacial period?.

AU: Hamelin,-B.; Bard,-E.; Zindler,-A.; Fairbanks,-R.G.

AF: Geosci. de l'Environn., Case 431, Univ. St. Jerome, 13397 Marseille, France

SO: EARTH-PLANET.-SCI.-LETT. 1991. vol. 106, no. 1-4, pp. 169-180

LA: English

ER: M (Marine)

AB: Direct measurement of U and Th by mass spectrometry recently provided a spectacular improvement in the precision of coral dating by the U-Th disequilibrium method. Mass spectrometric data also provide a much better resolution for the examination of subtle diagenetic effects revealed by small variations of the super(234)U/ super(238)U ratio. Such perturbations may strongly affect the accuracy of the U-Th chronometer. A compilation of all the corals analyzed to date by mass spectrometry shows that most of the corals from terraces of the last interglacial have initial super(234)U/ super(238)U ratios higher than present-day seawater, in contrast to modern, Holocene and last Glacial corals. Some samples that have very high super(234)U/ super(238)U initial ratios, up to 1.2, and high U concentrations, up to 4 ppm, were probably contaminated by continental groundwaters. However, even apparently pristine samples have super(234)U/ super(238)U initial ratios which are still slightly higher than present-day seawater (mean value: 1.160, compared to 1.140-1.150 (2)), with little overlap between the two distributions. This difference in the U initial ratio raises some uncertainty about the accuracy of the U-Th age determinations of these corals.

AN: 2730177

17 of 25

TI: Geochronology and petrogenesis of MORB from the Juan de Fuca and Gorda ridges by super(238)U- super(230)Th disequilibrium.

AU: Goldstein,-S.J.; Murrell,-M.T.; Janecky,-D.R.; Delaney,-J.R.; Clague,-D.A.

AF: Isotope Geochem., Group INC-7, Los Alamos Natl. Lab., Los Alamos, NM 87545, USA

SO: EARTH-PLANET.-SCI.-LETT. 1991. vol. 107, no. 1, pp. 25-41

LA: English

ER: M (Marine)

AB: A highly precise mass spectrometric method of analysis was used to determine super(238)U- super(234)U- super(230)Th- super(232)Th in axial and off-axis basalt glasses from Juan de Fuca (JDF) and Gorda ridges. Initial super(230)Th activity excesses in the axial samples range from 3 to 38%, but generally lie within a narrow range of 12 to 15%. Secondary alteration effects were evaluated using delta super(234)U and appear to be negligible; hence the super(230)Th excesses are magmatic in origin. Direct dating of MORB was accomplished by measuring the decrease in excess super(230)Th in off-axis samples. super(238)U- super(230)Th ages progressively increase with distance from axis. Uncertainties in age range from 10 to 25 ka for U-Th ages of 50 to 200 ka. The full spreading rate based on U-Th ages for Endeavour segment of JDF is 5.9 plus or minus 1/2 cm/yr, with asymmetry in spreading between the Pacific (4.0 plus or minus 0.6 cm/yr) and JDF (1.9 plus or minus 0.6 cm/yr) plates. For northern Gorda ridge, the half spreading rate for the JDF plate is found to be 3.0 plus or minus 0.4 cm/yr. These rates are in agreement with paleomagnetic spreading rates and topographic constraints.

AN: 2729181

18 of 25

TI: Geochronology and petrogenesis of MORB from the Juan de Fuca and Gorda ridges by super(238)U- super(230)Th disequilibrium.

AU: Goldstein,-S.J.; Murrell,-M.T.; Janecky,-D.R.; Delaney,-J.R.; Clague,-D.A.

AF: Isotope Geochem., Group INC-7, Los Alamos Natl. Lab., Los Alamos, NM 87545, USA

SO: EARTH-PLANET.-SCI.-LETT. 1992. vol. 109, no. 1-2, pp. 255-272

LA: English

ER: M (Marine)

AB: Erratum: A production error led to the publication of an uncorrected version of this paper. The corrected version is reprinted in full.

AN: 2713868

19 of 25

TI: Studies of scavenging phenomenon in the upper water column off northeast Taiwan--applications of super(234)Th/ super(238)U disequilibrium.

AU: Wei,-Ching-Ling

AF: Inst. Oceanogr., Natl. Taiwan Univ., Taipei, Taiwan

SO: ACTA-OCEANOGR.-TAIWAN. 1991. vol. 26, pp. 13-19

LA: English

ER: M (Marine)

AB: The first set of super(234)Th and super(238)U profiles in the water column northeast of Taiwan was reported. Th-234 activities are lower than its progenitor super(238) U in the upper part of the water column. The deficiency of super(234)Th relative to super(238)U in the upper 200 m was about 1.15 x 10 super(5) dpm m super(-2), which gives a residence time of similar to 122 days and an estimated flux of about 3000 dpm m super(-2)/d for super(234)Th in the upper water column.

AN: 2695842

20 of 25

TI: U-Th isotopic systematics at 13 degree N east Pacific Ridge segment.

AU: Ben-Othman,-D.; Allegre,-C.J.

AF: Lab. Geochim. Isot., URA 1371, Dep. Sci. Terre, Univ. Montpellier II, Place E. Bataillon, 34095 Montpellier Cedex 5, France

SO: EARTH-PLANET.-SCI.-LETT. 1990. vol. 98, no. 1, pp. 129-137

LA: English

ER: M (Marine)

AB: Fresh basaltic glasses were analyzed for U-Th disequilibrium systematics as part of an extensive study on the East Pacific Rise (EPR) at 12 degree 45'N. Samples are well described in terms of major and trace elements as well as in Nd, Pb and Sr isotopes. Results show significant heterogeneities in the mantle source at a small scale, and show heterogeneities at larger scales also when compared to other EPR data. U and Th concentration and isotopic data rule out fractional crystallization as a main process and support a mixing model in agreement with the marble cake model developed by Allegre and Turcotte and constrained by trace elements and Nd, Sr and Pb isotopes on the same samples by Prinzhofer et al. Based on the high ( super(230)Th/ super(232)Th) isotopic ratios on recent tholeiites especially the Th/U values inferred for their sources clearly show that the upper mantle Th/U has decreased with time.

AN: 2355521

21 of 25

TI: super(230)Th/ super(238)U and super(226)Ra/ super(230)Th fractionation in young basaltic glasses from the East Pacific Rise.

AU: Reinitz,-H.; Turekian,-K.K.

AF: Dep. Geol. and Geophys., Yale Univ., Box 6666, New Haven, CT 06511, USA

SO: EARTH-PLANET.-SCI.-LETT. 1989. vol. 94, no. 3-4, pp. 199-207

LA: English

ER: M (Marine)

AB: Mid-ocean ridge basalt (MORB) glasses treated to remove manganese and iron oxyhydroxide coatings containing U and Th decay chain nuclides sequestered from the ambient aqueous environment show little fractionation of ( super(230)Th) from ( super(238)U), but extensive enrichment of ( super(226)Ra) over ( super(230)Th). Chronometry based on ( super(230)Th)-( super(238)U) disequilibrium yields a mean age of 151,000 plus or minus 55,000 (2 sigma ) years ago for Th-U fractionation, from a source region with Th/U (atom ratio) = 1.58 plus or minus 0.43 (2 sigma ). ( super(226)Ra) excesses over ( super(230)Th) indicate an enrichment event more recent than the fractionation of Th from U. ( super(226)Ra/ super(230)Th) correlates well with K/U, providing a rough means of estimating the age since eruption of MORB glasses.

AN: 2266532

22 of 25

TI: super(230)Th/ super(238)U and super(226)Ra/ super(230)Th fractionation in young basaltic glasses from the East Pacific Rise.

AU: Reinitz,-I.; Turekian,-K.K.

AF: Dep. Geol. and Geophys., Yale Univ., Box 6666, New Haven, CT 06511, USA

SO: EARTH-PLANET.-SCI.-LETT. 1989. vol. 94, no. 3-4, pp. 199-207

LA: English

ER: M (Marine)

AN: 2152226

23 of 25

TI: super(234)U/ super(238)U disequilibrium in natural waters. Possible enrichment in super(234)U from a super(234)Th- super(234)U chromatographic separation process on silica.

OT: Le desequilibre isotopique super(234)U/ super(238)U dans les eaux naturelles. Possibilite de leur enrichissement en super(234)U a partir d'une separation super(234)Th- super(234)U par effet chromatographique sur silice a l'interface eau-roche

AU: Clanet,-F.; Deloncle,-R.; Ducos-Fonfrede,-S.

AF: Lab. Chim. et Hydrol., Fac. Pharm., Bio-Inorg 2bis Blvd. Tonnelle, 37042 Tours, France

SO: SCI.-EAU. 1987. vol. 6, no. 2, pp. 169-177

LA: French

ER: F (Freshwater)

AB: super(234)U/ super(238)U disequilibrium in natural waters is the result of different physical and chemical processes from which an enrichment in super(234)U in water flowing through aquifer rocks is the result. With porous and cracked granites, the possibility of a thorium-uranium separation by adsorption chromatography on silice is experimentally verified in proceeding by elution of super(234)U super(4+) and super(234)UO sub(2) super(2+) with flowing waters from super(234)Th super(4+) ions adsorbed on the water-rock interface. The result of this chromatographic effect the discharge of super(234)U dopped uranium which is added to super(234)U coming from super(234)Th nuclides ejected from the rock in the aqueous phase.

AN: 1984254

24 of 25

TI: Oceanic stratified euphotic zone as elucidated by super(234)Th: super(238)U disequilibria.

AU: Coale,-K.H.; Bruland,-K.W.

AF: Inst. Mar. Sci., Univ. California, Santa Cruz, CA 95064, USA

SO: LIMNOL.-OCEANOGR. 1987. vol. 32, no. 1, pp. 189-200

LA: English

ER: M (Marine)

AN: 1743374

25 of 25

TI: The application of uranium series disequilibrium concepts to sediment yield determination.

AU: Plater,-A.J.; Dugdale,-R.E.; Ivanovich,-M.

AF: Dep. Geogr., Nottingham Univ., Nottingham NG7 2RD, UK

SO: EARTH-SURF.-PROCESS.-LANDFORMS. 1988. vol. 13, no. 2, pp. 171-182

LA: English

ER: F (Freshwater)

AB: The determination of uranium series disequilibria in fluvial environments is proposed as a method of calculating catchment mass balances. The technique is based on two main principles. Firstly, super(234)U is more mobile than super(238)U, especially during the early stages of weathering. Secondly, uranium is far more mobile than either thorium or protactinium. Consequently, leaching during weathering results in the loss of the uranium found in the fresh rock, leaving the two immobile daughters behind. The ratio of uranium carried by sediment to that dissolved, U sub(S)/U sub(W) can, therefore, be determined from river water and sediment isotopic activity ratios. Fluxes of uranium can then be calculated from average concentrations in the water and the associated sediment, from which a sediment yield can be inferred.

AN: 1700731

No. Records Request

1: 60 THORIUM

2: >54 DISEQUILIBRI*

3: 12 THORIUM and DISEQUILIBRI*

Searches and records above from: ASFA 1997-1998/09

5: 25 #3

Searches and records above from: ASFA 1988-1996

7: 14 #5

1 of 14

TI: Seasonal variation in the difference between observed and calculated particulate fluxes of Th-234 in Funka Bay, Japan.

AU: Tsunogai,-S.; Taguchi,-K.; Harada,-K.

AF: Dep. Chem., Fac. Fish., Hokkaido Univ., Hakodate 041, Japan

SO: J.-OCEANOGR.-SOC.-JAPAN. 1986. vol. 42, no. 2, pp. 91-98

LA: English

ER: M (Marine)

AB: Particulate fluxes were determined by two methods to elucidate the behavior of settling particles in seawater. One method involves direct observation of fluxes with sediment traps, while in the other method flux is indirectly calculated from the radioactive disequilibrium between U-238 and Th-234 in seawater, which gives net flux. Observations were carried out several times throughout a year in Funka Bay. When linearly extrapolated, the observed gross fluxes of Th-234 did not converge to zero at the surface. In the subsurface water the difference between the observed and calculated fluxes showed a seasonal variation.

AN: 1554400

2 of 14

TI: super(234)Th: super(238)U disequilibria within the California Current.

AU: Coale,-K.H.; Bruland,-K.W.

AF: Cent. for Mar. Stud., Univ. California, Santa Cruz, CA 95064, USA

SO: LIMNOL.-OCEANOGR. 1985. vol. 30, no. 1, pp. 23-33

LA: English

ER: M (Marine)

AB: Profiles of dissolved and particulate super(234)Th were determined at several stations within the California Current. Modeling of the disequilibria between the super(234)Th and super(238)U within the surface waters provides for estimates of the residence time of dissolved thorium with respect to particle scavenging ( tau sub(d) varies from 6 to 50 days), the particle residence time ( tau sub(p) varies from 2 to 20 days), and the particulate super(234)Th flux exiting the surface layer. The model-derived, first-order scavenging rate constant for dissolved thorium is observed to be proportional to the rate of primary production. Particle residence times seem to be governed by the rate of zooplankton grazing and the types of zooplankton present. Model-derived particulate super(234)Th fluxes are in good agreement with direct measurements by sediment traps.

AN: 0923089

3 of 14

TI: super(230)Th- super(238)U disequilibrium in island arcs: Evidence from the Aleutians and the Marianas.

AU: Newman,-S.; MacDougall,-J.D.; Finkel,-R.C.

AF: Div. Geol. and Planet Sci., California Inst. Technol., Pasadena, CA 91125, USA

SO: NATURE. 1984. vol. 308, no. 5956, pp. 268-270

LA: English

ER: M (Marine)

AB: Because the Th/U ratio is quite different for each possible magma sources, and as Th and U may behave differently during fractionation processes, particularly if volatile transport is involved, studies of super(230)Th- super(238)U disequilibrium have great potential in investigations of arc lavas. Data given here, imply that the Th/U ratio in the sources of Marianas and Aleutian Island Arc lavas is similar to ocean ridge basalt sources, although there is a hint of a somewhat lower Th/U component in the Aleutian source. The data also confirm and extend the observations by Gill and Allegre and Condomines that oceanic arc lavas are distinguished from magmas erupted in virtually all other volcanic environments by activity ratios ( super(230)Th/ super(238)U) less than or equal to 1, implying relative enrichment of uranium.

AN: 0890008

4 of 14

TI: The use of super(234)Th/ super(238)U disequilibrium to examine the fate of particle-reactive species on the Yangtze continental shelf.

AU: McKee,-B.A.; DeMaster,-D.J.; Nittrouer,-C.A.

AF: Dep. Mar., Earth and Atmos. Sci., North Carolina State Univ., Raleigh, NC 27695-8208, USA

SO: EARTH-PLANET.-SCI.-LETT. 1984. vol. 68, no. 3, pp. 431-442

LA: English

ER: M (Marine); B (Brackish)

AB: Measurements of super(234)Th (t sub(1/2)=24.1 d) in water column and seabed samples from an area near the mouth of the Yangtze River (People's Republic of China) provide the following information: Most of the super(234)Th in waters near the mouth of the Yangtze River is in particulate form, and horizontal transport and sedimentation of super(234)Th-bearing particles dominate the super(234)Th budget in this area. A model incorporating processes in at least two dimensions is required to understand the fate of particle-reactive species on the Yangtze continental shelf. The residence times of particle-reactive species (with respect to scavenging) range from 0.3 days (nearshore) to 4.0 days (offshore). The residence times (with respect to removal to the seabed) range from 0.5 day (nearshore) to 11.0 days (offshore). Scavenging residence times for super(234)Th decrease as the concentration of suspended particles increases. The time for removal of super(234)Th to the seabed increases with distance from shore (a variable which integrates such factors as scavenging rate, bathymetry, and frequency of resuspension).

AN: 0812961

5 of 14

TI: super(230)Th- super(238)U disequilibrium systematics in oceanic tholeiites from 21 degree N on the East Pacific Rise.

AU: Newman,-S.; Finkel,-R.C.; MacDougall,-J.D.

AF: Geol. Res. Div., A-020, Scripps Inst. Oceanogr., La Jolla, CA 92093, USA

SO: EARTH-PLANET.-SCI.-LETT. 1983. vol. 65, no. 1, pp. 17-33

LA: English

ER: M (Marine)

AB: Significant disequilibrium occurs between super(230)Th and its parent, super(238)U, in a suite of fresh basalt glasses from the RISE Project study area at 21 degree N on the East Pacific Rise. The ( super(230)Th/ super(232)Th) activity ratios observed for eight of nine samples from the crest of the axis at this site are constant within analytical uncertainty, with a value of 1.22. This observed homogeneity of ( super(230)Th/ super(232)Th) has two possible interpretations. First, the measured ( super(230)Th/ super(232)Th) can be considered to indicate a mantle-source for the RISE basalts with Th/U of 2.5. This interpretation, however, conflicts with the proposed correlation between ( super(230)Th/ super(232)Th) and super(87)Sr/ super(86)Sr (1) which predicts that ( super(230)Th/ super(232)Th) should equal 1.33 at the RISE site. A second possible interpretation is that radioactive decay of super(230)Th, in the basalts themselves or in a magma chamber, has decreased ( super(230)Th/ super(232)Th) from 1.33 to the observed values. The required time span is 11,000 to > 100,000 years. However, petrologic arguments rule against long residence time in a magma chamber, and the spreading rate of this section of the East Pacific Rise (6 cm/yr) predicts that the maximum age for axis basalts is 27,000 years.

AN: 0621994

6 of 14

TI: Thorium series disequilibrium and geochemical processes in estuarine sediments of Mandovi River.

AU: Joshi,-L.U.; Zingde,-M.D.; Abidi,-S.A.H.

AF: Air Monitoring Sec., Bhabha Atom. Res. Cent., Bombay-400 085, India

SO: J.-RADIOANAL.-CHEM. 1983. vol. 77, no. 1, pp. 57-64

LA: English

ER: B (Brackish)

AB: The measurements of natural radioactivity due to thorium isotopes have been carried out in estuarine sediments of Mandovi river (Goa). The geochemical behaviour of these sediments has been studied by leaching the samples with 5% ethylene diaminetetraacetic acid at pH 3.0 in order to investigate the processes occurring on the surface of the sediment particles and the distribution of natural thorium in estuarine sediments. The super(228)Th/ super(232)Th activity ratios have been found to be in the range of 2.00 to 2.12. This anomaly between super(232)Th and super(228)Th has been attributed to the preferential leaching of super(228)Ra by water flowing over these sediments. The activities of super(228)Ra on the surface labile layers of the sediments have also been determined. The super(230)Th/ super(232)Th activity ratios have been found to be in the range of 0.94 to 1.04. These ratios are mainly dependent on the precipitation action of super(230)Th on adjacent sediments.

AN: 0587961

7 of 14

TI: Radioactive Disequilibrium of Thorium Series Nuclides in Surface Waters of the Seto Inland Sea.

AU: Okubo,-T.

AF: Dep. Nuclear Engineering, Kobe Univ., Mercantile Marine, Fukaeminamimachi, Higashinada-ku, Kobe 658, Japan

SO: J.-OCEANOGR.-SOC.-JAP. 1982. vol. 38, no. 1, pp. 1-7

LA: English

AB: Surface samples of sea water collected in the Seto Inland Sea were anlyzed for super(232)Th and super(228)Th. The concentrations of super(232)Th were generally less than 2 dpm/1,000 l and these values are probably an upper limit for the super(232)Th concentration in surface waters of the Seto Inland Sea. The super(228)Th concentrations ranged between 4.2 to 42.3 dpm/1,000 I. Remarkable seasonal and temporal variations in super(228)Th concentrations were found, in comparison with the minimal variations in super(228)Ra concentrations reported previously. The activity ratios of super(228)Th/ super(228)Ra were about 0.18 in the southern part of the Kii and the Bungo Channels, and decreased markedly from the open ocean toward the central region of the Seto Inland Sea.

AN: 0231585

8 of 14

TI: Removal of ~SUP-234~Th from a coastal sea: Funka Bay, Japan.

AU: Minagawa,M.; Tsunogai,S.-(Mitsubishi-Kasei-Inst.-Life-Sci.,-Minami-Ohya,-Machida,-Tokyo-194,-Japan)

SO: Earth-Planet.-Sci.-Lett., 1980 47(1), 51-64

LA: English

ER: M (Marine)

AB: In Funka Bay of Hokkaido, Japan, seawater, suspended matter and settling matter were collected once every month in the summer of 1974. These samples were analyzed for SUP-234Th, a short-lived daughter of dissolved SUP-238U. A pronounced disequilibrium between SUP-234Th and SUP-238U, and a highly variable concentration of SUP-234Th were found. Positive correlation, however, exist among the deficiency of SUP-234Th relative to SUP-238U in seawater, the concentration of particulate SUP-2U3SUP-4Th, the fraction of particulate SUP-234Th to total SUP-234Th in seawater, the total dry weight of suspended matter, and the primary productivity during the month previous to sampling. The specific activity of SUP-234Th for the settling particles (620 170 dpm/g) was nearly equal to that for suspended particles (720 600 dpm/g) but much greater than that for plankton (47 24 dpm/g). These facts suggest that suspended particles are somehow closely related to the removal of heavy metals from seawater, in spite of the negligibly small settling flux of suspended matter. The residence time of thorium in Funka Bay (mean depth: 60 m) is found to be about 60 days, which is nearly equal to those of SUP-210Pb and SUP-210Po.

AN: 0114670

9 of 14

TI: Tracking particle-associated processes in nearshore environments by use of ~SUP-234~Th/~SUP-238~U disequilibrium.

AU: Aller,R.C.; Benninger,L.K.; Cochran,J.K.-(Dep.-Geophys.-Sci.,-Univ.-Chicago,-5734-S.-Ellis-Avenue,-Chicago,-IL-60637,-USA)

SO: Earth-Planet.-Sci.-Lett., 1980 47(2), 161-175

LA: English

ER: B (Brackish)

AB: Measurement of excess SUP-234Th (tSUB-1/2 = 24.1 days) in surface sediment from 12 stations throughout Long Island Sound, USA, demonstrates: (1) a mean (summer) sediment inventory of 3.6 dpm/cmSUP-2 consistent with complete, nearly instantaneous removal of SUP-234Th from the overlying water and capture within the estuary, and (2) preferential association of excess SUP-234Th with small particles and inventory build-ups in muddy bottom areas. There may also be a tendency for higher inventories in areas of high physical or biogenic reworking of surface sediments. A range of particle reworking rates (0-5 cm) from <0.01 x 10SUP--6 to 1.6 x 10SUP--6 cmSUP-2/s is found in the Sound with most values approx 0.2-0.5 x 10SUP--6 cmSUP-2/s. The inventory and reworking patterns demonstrate the high mobility, both horizontal and vertical, of particles in the estuary on SUP-234Th decay time scales and are unequivocal evidence for control of reactive element distribution in the water column by the muddy regions of the basin.

AN: 0115090

10 of 14

TI: ~SUP-228~Th-~SUP-228~Ra radioactive disequilibrium in the New York Bight and its implications for coastal pollution.

AU: Li,Y.-H.; Feely,H.W.; Santschi,P.H.-(Lamont-Doherty-Geol.-Obs.,-Columbia-Univ.,-Palisades,-NY-10964,-USA)

SO: Earth-Planet.-Sci.-Lett., 1979 42(1), 13-26

LA: English

ER: M (Marine)

AB: In the summer of 1975, the half removal time of SUP-228Th by settling particles, tSUB-c, was about 11 4, 29 8 and 70 10 days in the shelf surface water, the shelf winter water and the slope surface water of the New York Bight, respectively. In the fall of 1974, tSUB-c was about 17 1 to 28 2 days from the inner shelf to the outer shelf surface waters and about 70 10 days in the slope surface water. A simple box model of the shelf water in the Middle Atlantic Bight shows that (1) the exchange rate between the shelf and the slope waters is about 2500 800 kmSUP-3/yr, (2) the mean residence time of the shelf water is only about 132 36 days, and (3) the average SUP-226Ra and SUP-228Ra fluxes per unit area of the coastal sediments are about 0.05 dpm SUP-226Ra/cmSUP-2 yr and 0.37 dpm SUP-228Ra/cmSUP-2 yr. These rates are consistent with previously reported results. The implication of these rates to pollutants in the coastal environment is discussed.

AN: 9047080

11 of 14

TI: [Variability of the isotopes ratio of the 234 and 238 uranium in ground-water geology]. /[Explication par un processus de separation par adsorption differentielle du thorium et de l'uranium sur les roches silicatees et la silice].

OT: Variabilite de la teneur en isotopes de masses 234 et 238 de l'Uranium dans les systemes hydrogeologiques.

AU: Clanet,-F.-(Tours-Univ.,-Lab.-Chim.-Minerale-et-Hydrol.,-2-Bis-Bd-Tonnelle,-37032,-France)

SO: J.-Fr.-Hydrol., 1977 8(24), 113-122

LA: French

ER: F (Freshwater)

AB: The radioactivity study of water and aquifer granite of a hydrogeological system shows a -SUP-234-U--SUP-238-U disequilibrium in water and the localisation of -SUP-234-Th at the level of the aquifer rock. Laboratory experiments of thin layer chromatography on granite and silica powders realized with Th(OH)-SUB-4-, U(OH)-SUB-4- and UO-SUB-2-(OH)-SUB-2- shows that the localisation of -SUP-234-Th on the granite and the enrichment of water in -SUP-234-U may result from the -SUP-234-Th insolubilisation and from a separative effect between Th-SUP-+4-, U-SUP-+4- and U-SUP-+6- by an adsorption chromatography effect at the water-silicated rock interface. A geochemical model is proposed for the explanation of the establishment of -SUP-234-U--SUP-238-U dis-equilibrium states in Nature.

AN: 8003740

12 of 14

TI: Uranium and thorium series nuclides in oriented ferromanganese nodules: growth rates, turnover times and nuclide behavior.

AU: Krishnaswami,-S.; Cochran,-J.K.-(Phys.-Res.-Lab.,-Navrangpura,-Ahmedabad-380009,-India)

SO: Earth-Planet.-Sci.-Lett. 1978 40(1), 45-62

LA: English

ER: M (Marine)

AB: Three ferromanganese nodules handpicked from the tops of 2500 cm-SUP-2- area box cores taken from the north equatorial Pacific have been analysed for their U-Th series nuclides. -SUP-230-Th-SUB-exc- concentrations in the surface 1-2 mm of the top side of the nodules indicate growth rates of 1-.-8-4-.-6 mm/10-SUP-6- yr. In two of the nodules a significant discontinuity in the -SUP-230-Th-SUB-exc- depth profile has been observed at about 0-.-3 m.y. ago, suggesting that the nodule growth has been episodic. The concentration profiles of -SUP-231-Pa-SUB-exc- (measured via -SUP-227-Th) yield growth rates similar to the -SUP-230-Th-SUB-exc- data. The bottom sides of the nodules display exponential decrease of -SUP-230-Th-SUB-exc-/-SUP-232-Th activity ratio with depth, yielding growth rates of 1-.-5-3-.-3 mm/10-SUP-6- yr. The -SUP-230-Th-SUB-exc- and -SUP-231-Pa-SUB-exc- concentrations in the outermost layer of the bottom face are significantly lower than in the outermost layer of the top face. Comparison of the extrapolated -SUP-230-Th-SUB-exc-/-SUP-232-Th and -SUP-230-Th-SUB-exc-/-SUP-231-Pa-SUB-exc- activity ratios for the top and bottom surfaces yields an 'age' of (5-15) x 10-SUP-4- yr for the bottom relative to the top. This 'age' most probably represents the time elapsed since the nodules have attained the present orientation. The -SUP-210-Pb concentration in the surface 0-.-1 mm of the top side is in large excess over its parent -SUP-226-Ra. Elsewhere in the nodule, up to about 1 mm depth in both top and bottom sides, -SUP-210-Pb is deficient relative to -SUP-226-Ra, probably due to -SUP-222-Rn loss. The absence of -SUP-210-Pb-SUB-exc- below the outermost layer of the top face rules out the possibility of a sampling artifact as the cause of the observed exponentially decreasing -SUP-230-Th-SUB-exc- and -SUP-231-Pa-SUB-exc- concentration profiles. The flux of -SUP-210-Pb-SUB-exc- to the nodules ranges between 0-.-31 and 0-.-58 dpm/cm-SUP-2- yr. The exhalation rate of -SUP-222-Rn, estimated from the -SUP-226-Ra--SUP-210-Pb disequilibrium is about 570 dpm/cm-SUP-2- yr from the top side and >2000 dpm/cm-SUP-2- yr from the bottom side. -SUP-226-Ra is deficient in the top side relative to -SUP-230-Th up to about 0-.-5-1 mm and is in large excess throughout the bottom. The data indicate a net gain of -SUP-226-Ra into the nodule, corresponding to a flux of (24-46) x 10-SUP--3- dpm/cm-SUP-2- yr. On a total area basis the gain of -SUP-226-Ra into the nodules is <20% of the -SUP-226-Ra escaping from the sediments.

AN: 8124650

13 of 14

TI: Radioactive disequilibrium in altered mid-oceanic basalts.

AU: Bacon,-M.P.-(Woods-Hole-Oceanogr.-Inst.,-Woods-Hole,-MA-02543,-USA)

SO: Earth-Planet.-Sci.-Lett., 1978 39(2), 250-254

LA: English

AB: A young (<1 m.y.) tholeiitic basalt dredged from the Mid-Atlantic Ridge displays a -SUP-234-U excess and a -SUP-230-Th deficiency that have resulted from the addition of seawater uranium during weathering at seafloor temperatures. Two older samples, though they acquired substantial amounts of uranium from seawater, are depleted in -SUP-234-U, indicating preferential leaching of this isotope. Hydrothermally altered samples suggest that some uranium loss may have occurred. Possible isotopic effects of preferential -SUP-234-U leaching, however, are obscured by secondary addition of seawater uranium at lower temperatures.

AN: 8102430

14 of 14

TI: Measurement of thickness of surface layer of the labile component of thorium and uranium present on marine sediment particle surface.

AU: Joshi,-L.U.; Ganguly,-A.K.-(Div.-Radiol.-Prot.,-Bhabha-At.-Res.-Cent.,-Trombay,-Bombay-400085,-India)

SO: Indian-J.-Mar.-Sci., 1977 6(1), 59-63

LA: English

ER: M (Marine)

AB: Surface of sediment particles covered with organic matter contain thorium and uranium in labile chemical form. Such labile components can be removed by destroying the organic matter on the sediment particles with phosphate-free hydrogen peroxide in presence of 0-.-05M hydrochloric acid and by many leaching agents. In the dynamic processes in the coastal environment chemical equilibria of the labile components are established between the surface of the particles and the ambient sea water. Particle size distribution for various marine sediment samples collected from the West coast of India has been determined. From these data, surface areas of particles (assumed spherical) participating in the physicochemical processes at the particle water interface have been calculated. Densities of particles with and without organic matter have been determined pycnometrically. The organic matter which is mainly humic and fulvic acids, has been extracted from the sediments and the density of the organic matter determined pycnometrically. An attempt is made to estimate the mean thickness of the surface layer participating in the leaching and equilibrium processes, wherein the disequilibrium of natural radioactive elements has been observed earlier by the authors. Thickness of the surface layer of the labile component of thorium and uranium in freshly powdered monazite mineral sand (for the surface of a dense material completely free of organic matter) is 1-.-13 x 10-SUP--6- and 1-.-60 x 10-SUP--6- cm respectively. Thickness of the labile organic layer of the coastal sediment particles is in the range 2-.-5 x 10-SUP--6- to 10 x 10-SUP--6- cm.

AN: 8083090