海水中234Th的超低水平液闪谱仪测定   总被引：2，自引：1，他引：2  

李鸿宾  黄奕普  陈敏  刘广山  邱雨生 《台湾海峡》2004,23(2):199-207

本文提出了利用超低水平液闪谱仪测定海水中234Th的方法.海水经氢氧化铁吸附共沉淀富集后,接着用阴离子交换和TBP/煤油萃取进行Th同位素的分离与纯化.对一系列测定条件进行了详细的研究,提出了测定海水中234Th的适宜程序,即在含有234Th和产额示踪剂230Th的纯化后的5mol/dm3HNO3溶液中加入TBP/煤油进行萃取,然后用0.1mol/dm3HNO3反萃取,后者是先用契伦柯夫计数法测量234Th(通过234mPa),后加入闪烁液Hisafe 3用α/β模式测量α放射体230Th.对于α和β放射体液闪谱仪的计数效率分别为100%和55.7%±2.7%.234Th的化学回收率和总探测效率分别为70%～80%和30%～45%.该法测定海水中的234Th快速、简便和高效.  相似文献   

南大洋普里兹湾基于234Th/238U不平衡法的POC输出通量研究   总被引：2，自引：0，他引：2       下载免费PDF全文

何建华  马豪  陈立奇  项宝强  曾宪章  尹明端  曾文义 《海洋学报》2007,29(4):69-76

中国第22次南极科学考察(2005年11月至2006年3月)期间,测定了南极普里兹湾海域5个站位的从表层至150 m水深的不同层位水样中溶解态和颗粒态234Th,238U的放射性比活度以及颗粒有机碳.利用234Th/238U在上层水体中的不平衡,计算了南极普里兹湾上层水体中234Th的平均停留时间和输出通量.结果显示,随着纬度的增加,上层水体中颗粒态和溶解态234Th的平均停留时间总体趋向减小,并在中纬度站位出现了最低值,分别为1~8和29~48 d,而颗粒态和溶解态234Th的输出通量则在中纬度站位出现了最大值,分别为21~38和26~39 dpm/(m3·d).运用箱型清除模式,利用两种不同的方法估算了各水柱中从真光层底部输出的POC通量,平均值分别达到104.7 mmol/(m2·d)(E法)和120.6 mmol/(m2·d)(B法),表明南极普里兹湾夏季存在很高的新生产力,它将会对该海域碳的生物泵过程产生重要作用.  相似文献   

Thorium isotopes as tracers of particles dynamics and deep water circulation in the Indian sector of the Southern Ocean (ANTARES IV)     

L. Coppola  M. Roy-Barman  S. Mulsow  P. Povinec  C. Jeandel 《Marine Chemistry》2006,100(3-4):299

Dissolved and particulate samples were collected to study the distribution of thorium isotopes (²³⁴Th, ²³²Th and ²³⁰Th) in the water column of the Indian sector of the Southern Ocean (from 42°S to 47°S and from 60°E to 66°E, north of the Polar Front) during Austral summer 1999. Vertical profiles of excess ²³⁰Th (²³⁰Th_xs) increases linearly with depth in surface water (0–100 m) and a model was applied to estimate a residence time relative to the thorium scavenging (τ_scav). Low τ_scav in the Polar Front Zone (PFZ) are found, compared to those estimated in the Subtropical Front Zone (STZ). Changes in particle composition between the PFZ and STZ could influence the ²³⁰Th_xs scavenging efficiency and explain this difference. An innovative coupling between ²³⁴Th and ²³⁰Th_xs was then used to simultaneously constrain the settling velocities of small (0.6–60 μm) and large (above 60 μm) particles. Although the different hydrological and biogeochemical regimes visited during the ANTARES IV cruise did not explain the spatial variation of sinking velocity estimates, our results indicate that less particles may reach the seafloor north (60 ± 2 m d^− 1, station 8) than south of the Agulhas Return Current (119 ± 23 and 130 ± 5 m d^− 1 at stations 3 and 7, respectively). This information is essential for understanding particle transport and by extension, carbon export. In the deep water column, the ²³⁰Th_xs concentrations did not increase linearly with depth, probably due to lateral transport of North Atlantic Deep Water (NADW) from the Atlantic to the Indian sector, which renews the deep waters and decreases the ²³⁰Th_xs concentrations. A specific ²³⁰Th_xs transport model is applied in the deep water column and allows us to assess a “travel time” of NADW ranging from 2 to 15 years.  相似文献   

Th sorption and export models in the water column: A review   总被引：2，自引：3，他引：2  

Nicolas Savoye  Claudia Benitez-Nelson  Adrian B. Burd  J. Kirk Cochran  Matthew Charette  Ken O. Buesseler  George A. Jackson  Matthieu Roy-Barman  Sabine Schmidt  Marc Elskens 《Marine Chemistry》2006,100(3-4):234

Over the past few decades, the radioisotope pair of ²³⁸U / ²³⁴Th has been widely and increasingly used to describe particle dynamics and particle export fluxes in a variety of aquatic systems. The present paper is one of five review articles dedicated to ²³⁴Th. It is focused on the models associated with ²³⁴Th whereas the companion papers (same issue) are focused on present and future methodologies and techniques (Rutgers van der Loeff et al.), C / ²³⁴Th ratios (Buesseler et al.), ²³⁴Th speciation (Santschi et al.) and present and future applications of ²³⁴Th [Waples, J.T., Benitez-Nelson, C.R., Savoye, N., Rutgers van der Loeff, M., Baskaran, M., Gustafsson, Ö., this issue. An Introduction to the application and future use of ²³⁴Th in aquatic systems. Marine Chemistry, FATE special issue]. In this paper, we review current ²³⁴Th scavenging models and discuss the relative importance of the non-steady state and physical terms associated with the most commonly used model to estimate ²³⁴Th flux. Based on this discussion we recommend that for future work the use of models should be accompanied by a discussion of the effect that model and data uncertainty have on the model results. We also suggest that future field work incorporate repeat occupations of sample sites on time scales of 1–4 weeks in order to evaluate steady state versus non-steady state estimates of ²³⁴Th export, especially during high flux events (> ca. 800 dpm m^− 2 d^− 1). Finally, knowledge of the physical oceanography of the study area is essential, particularly in ocean margins and in areas of established upwelling (e.g., Equatorial Pacific). These suggestions will greatly enhance the application of ²³⁴Th as a tracer of particle dynamics and flux in more complicated regimes.  相似文献   

真光层的颗粒动力学──Ⅵ.南海东北部海域上层水体颗粒动力学的示踪研究     

陈敏  黄奕普  陈飞舟  邱雨生  徐茂泉  姜德盛 《热带海洋学报》1997,(2)

利用234Th－238U不平衡研究南海东北部海域3个站位上层水体中的颗粒动力学性质，测定了水往中溶解态及颗粒态234Th的比活度，具体讨论各相中234Th／238U）AR（放射性活度比）比值的垂直分布情况及其与水化学要素间的关系。运用稿态箱式模型计算出各站位不同水层中溶解态234Th相对于清除至颗粒物的平均停留时间和颗粒态234Th相对于迁出作用的停留时间。由模型得出的参数表明3个站位的真光层具有两种不同的层化图像，这一情形与我们在南沙群岛海域得到的结果相一致。结合POC／PTh比值，估算出3个站位从真光层输出的颗粒有机碳（POC）通量分别为4.025.0和5．4mmolC·m－3－d-1。文中进一步讨论了234Th与POC两者停留时间的关系。  相似文献   

The POC / Th ratio of settling particles isolated using split flow-thin cell fractionation (SPLITT)     

rjan Gustafsson  Jenny Larsson  Per Andersson  Johan Ingri 《Marine Chemistry》2006,100(3-4):314

The common assumption that the ratio between particulate organic carbon (POC) and particulate ²³⁴Th obtained from shallow sediment traps and filterable particles are representative of the ratio in the total particle settling flux should be treated with caution in view of well-known biases associated with tethered shallow sediment traps and the decoupling between size and settling velocity of many natural particle regimes. To make progress toward reliably constraining the POC / ²³⁴Th ratio on truly settling particles, we have tested here a settling collection technique designed to remove any hydrodynamic bias; split flow-thin cell fractionation (SPLITT). These first results from a North Sea fjord and an open Baltic Sea time-series station indicates that the POC / ²³⁴Th ratio on the more complete particle-settling spectrum, isolated with SPLITT, was higher than the POC / ²³⁴Th ratio obtained simultaneously from tethered shallow sediment traps in seven out of seven parallel deployments with an average factor of 210%. The POC / ²³⁴Th ratio from the SPLITT was either in the same range or higher than that obtained on filtered “bulk” particles. To explain this novel data we hypothesize that the slowest settling fraction is organic-matter rich and does not strongly complex ²³⁴Th (i.e., high POC / ²³⁴Th). We suggest that this ultra-slow sinking fraction is better collected by SPLITT than with tethered sediment traps because of minimized hydrodynamic bias.This was tested using the ratio of POC / Al as a tracer of detrital mineral-ballast influenced settling velocity. The higher POC / Al ratios in SPLITT samples relative to in traps is consistent with the hypothesis that SPLITT is better suited for collecting also the slow-settling component of sinking particles. This important slow-settling component appears to here consist primarily of non-APS/TEP components of plankton exudates or other less-strongly ²³⁴Th-complexing organic matter. Further applications of the SPLITT technique are likely to return increasingly new insights on the composition (including “truly settling” POC / ²³⁴Th) of the total spectrum of particles settling out of the upper ocean.  相似文献   

The Meso-Cenozoic thermo-tectonic evolution of the Eastern Pyrenees: an <Superscript>40</Superscript>Ar/<Superscript>39</Superscript>Ar fission track and (U–Th)/He thermochronological study of the Canigou and Mont-Louis massifs     

O. Maurel  P. Moniè  R. Pik  N. Arnaud  M. Brunel  M. Jolivet 《International Journal of Earth Sciences》2008,97(3):565-584

Vertical displacements on the SW–NE T&#234;t fault (Eastern Pyrenees Axial Zone, France), which separates the Variscan Canigou-Carança and Mont-Louis massifs, were constrained using a thermochronologic multi-method approach. ⁴⁰Ar/³⁹Ar data from the granitic Mont-Louis massif record its Variscan cooling history and reveal no ages younger than Early Cretaceous, while the Canigou-Carança gneiss massif records systematically younger ⁴⁰Ar/³⁹Ar ages. These younger ⁴⁰Ar/³⁹Ar ages in the Canigou-Carança gneiss massif are the result of partial to total rejuvenation of argon isotopic systems related to a thermal flow coeval with the Cretaceous HT-BP metamorphism in the North Pyrenean Zone. Only the deepest rocks from the Canigou-Carança suffered this extensive Mid-Cretaceous thermal overprint probably due to differential burial around 4 km at that time. The post Mid-Cretaceous vertical displacements along the T&#234;t fault are recorded by “low” temperature thermochronology using K-feldspar ⁴⁰Ar/³⁹Ar, zircon and apatite fission track and (U–Th)/He datings. The Mont-Louis granite samples experienced a long period of protracted cooling reflecting a lack of thermo-tectonic activity in this area from Late Palaeozoic to Early Cenozoic, followed by cooling from 55–60 Ma to Late Eocene at a mean rate of 15–20°C/Ma in the final stage. This cooling stage corresponds to T&#234;t fault reactivation with a reversed component, promoting exhumation of the Mont-Louis roof zone contemporaneously with the south-vergent Pyrenean thrusting. In the Canigou-Carança massif, the main cooling event occurred from 32 to 18 Ma at a maximum rate of 30°C/Ma during Early Oligocene followed by a more moderate rate of 3°C/Ma from Late Oligocene to Early Burdigalian, coeval with the normal reactivation of the T&#234;t fault in brittle conditions that accommodated the final exhumation of the massif during the opening of the Gulf of Lion.  相似文献   

Subarcsec 10μm imaging of bipolar flow sources     

S. Cabrit  P. O. Lagage  E. Pantin 《Experimental Astronomy》1994,3(1-4):151-152

We have started a program of high-resolution (0.4/pixel) 10m imaging of bipolar outflow sources using the 10m camera CAMIRAS. We present recent results obtained at the Canada France Hawaii Telescope which reveal extended emission or IR companions in several luminous objects. The extended emission we detected probably arises from transiently heated very small grains, while the newly discovered companions could contribute significantly to the outflow activity and extended far-IR emission usually attributed to the main optical source.  相似文献   

Les failles récentes des Grands-Moulins (Savoie) : un Sackung (tassement gravitaire) majeur dans les Alpes françaises     

Jean-Claude Hippolyte  Marc Tardy  Gérard Nicoud 《Comptes Rendus Geoscience》2006,338(10):734-741

In Savoy, the Grands-Moulins recent fault scarps, previously interpreted as seismic fault ruptures, are in fact part of a major Sackung (deep seated gravitational spreading) of the French Alps (9 km long). We mapped more than 60 sackung scarps, some of them reaching 1330 m long and 30 m high. These antislope scarps stop the active screes and offset relict Dryassic rock glaciers by 16 m. We present geomorphologic observations attesting for their gravitational origin. This Sackung is primarily due to glacial debuttressing, while seismic shaking could be a triggering mechanism. To cite this article: J.-C. Hippolyte et al., C. R. Geoscience 338 (2006).  相似文献   

Environmental evolution of Zoigê Basin since 900 kaB.P. and comparison study with Loess Plateau     

Sumin Wang  Bin Xue 《中国科学D辑(英文版)》1997,40(3):329-336

The Zoige Basin is located in the eastern margin of the Qinghai-Xizang Plateau, in which two cores, RH and RM, have been drilled, with the depths of 120 m and 310 m respectively. The former with the bottom age of 826 kaB. P. has been divided into 21 stages according to the multi-proxy analysis, which could be basically compared with the oxygen isotope record of deep-sea core. The palaeoclimatic and palaeoenvironmental process of the Zoig&#234; Basin over the past 900 kaB. P. is reconstructed, and the comparison of core RH with the Luochuan Loess record is made.  相似文献