An improvement in the small-volume technique for determining thorium-234 in seawater

The recently developed 2–5 L small-volume MnO₂ coprecipitation method for determining ²³⁴Th in seawater has provided a new way to substantially increase, both temporally and spatially, the sampling resolution of ²³⁴Th and ²³⁴Th-based particulate organic carbon export estimates in the upper ocean. In this study, we further optimize the technique by reducing reagent quantities and the use of an additional water bath heating step. This optimization allows the filtration of the MnO₂ precipitate onto a 25-mm diameter, 1.0 μm pore size QMA filter to be completed within < 30 min for unfiltered waters from the South China Sea. In addition, we have modified the MnO₂ purification procedure to allow for alpha spectrometric measurements of ²³⁴Th recoveries. Results from recovery experiments suggest that reagent amounts can be reduced to 0.0375 mg KMnO₄ and 0.1 mg MnCl₂·4H₂O per liter of sample, while still maintaining high ²³⁴Th recovery. This study further confirms that the addition of a yield monitor is necessary for the application of the small-volume method.     

An in-situ analysis and measurement of thorium-234, uranium isotopes in seawater

A low-level β counting-α spectrum apparatus used for the detection of the β radiation of thorium-234 and α spectrum of thorium-228 simultaneously and an easy operating procedure for the enrichment, radiochemical separating, sampling and measurement of thorium-234 and uranium-238 in the ocean are developed based on the requirements of analyzing export productivity in the euphotic zone via thorium-234-uranium-238 radioactivity disequilibrium. The detecting efficiency both of β and α radiation is higher than 20%. The background of β radiation is less than 0.5 min-1, and the energy resolution of α detector is better than 1%. Total recycle ratio of thorium-234 is about 75%. Using the above apparatus and procedure, the radioactivities of dissolved thorium-234 and uranium-238, particle thorium-234 and uranium-238 in seawater of the South China Sea, the Southern Ocean and the Arctic Ocean were analyzed.     

A community-wide intercomparison exercise for the determination of dissolved iron in seawater

The first large-scale international intercomparison of analytical methods for the determination of dissolved iron in seawater was carried out between October 2000 and December 2002. The exercise was conducted as a rigorously “blind” comparison of 7 analytical techniques by 24 international laboratories. The comparison was based on a large volume (700 L), filtered surface seawater sample collected from the South Atlantic Ocean (the “IRONAGES” sample), which was acidified, mixed and bottled at sea. Two 1-L sample bottles were sent to each participant. Integrity and blindness were achieved by having the experiment designed and carried out by a small team, and overseen by an independent data manager. Storage, homogeneity and time-series stability experiments conducted over 2.5 years showed that inter-bottle variability of the IRONAGES sample was good (< 7%), although there was a decrease in iron concentration in the bottles over time (0.8–0.5 nM) before a stable value was observed. This raises questions over the suitability of sample acidification and storage.     

Analysis of seawater for dissolved cadmium, copper and lead: An intercomparison of voltammetric and atomic absorption methods

An intercomparison study of voltammetric and atomic absorption spectrometric methods for determining cadmium, lead and copper in seawater samples was conducted. The voltammetric approach utilizes differential pulse anodic stripping voltammetry using a rotating, glassy carbon, mercury film electrode under conditions developed to minimize contamination sources and to enhance sensitivity for seawater matrices. The atomic absorption approach involves a concentration step using either an organic solvent extraction of metal dithiocarbamate chelates or a Chelex-100 column with detection by graphite furnace atomic absorption spectrometry. Similar and consistent results were obtained using both methods for the three trace metals studied on a wide range of natural seawater samples. Both methods are comparable in sensitivity for cadmium and copper, however the voltammetric method is better suited for the analysis of lead in seawater because of its enhanced sensitivity and low blank. An advantage of the voltammetric approach is its amenability towards real-time shipboard analysis.     

Regional estimates of POC export flux derived from thorium-234 in the western Arctic Ocean

1Introduction CarboncyclingintheArcticOceanplaysanim- portantroletoglobalchange.Traditionally,marine productivityintheArcticOceanisthoughttobevery low,andthussomebiogeochemicalprocessessuchas particleexportandcyclingofnutrientsarenotsoac- tivebecauseofthembeingcoveredperenniallybyice, lowtemperatureandshorttimeofphotosynthesis (PlattandRao,1975).Afewpreviousestimatesof particulateorganiccarbon(POC)exportindicateda neglectablemagnitudeinthecentralArcticOcean (Baconetal.,1989).However,recen…     

An assessment of particulate organic carbon to thorium-234 ratios in the ocean and their impact on the application of Th as a POC flux proxy

Thorium-234 is increasingly used as a tracer of ocean particle flux, primarily as a means to estimate particulate organic carbon export from the surface ocean. This requires determination of both the ²³⁴Th activity distribution (in order to calculate ²³⁴Th fluxes) and an estimate of the C / ²³⁴Th ratio on sinking particles, to empirically derive C fluxes. In reviewing C / ²³⁴Th variability, results obtained using a single sampling method show the most predictable behavior. For example, in most studies that employ in situ pumps to collect size fractionated particles, C / ²³⁴Th either increases or is relatively invariant with increasing particle size (size classes > 1 to 100s μm). Observations also suggest that C / ²³⁴Th decreases with depth and can vary significantly between regions (highest in blooms of large diatoms and highly productive coastal settings). Comparisons of C fluxes derived from ²³⁴Th show good agreement with independent estimates of C flux, including mass balances of C and nutrients over appropriate space and time scales (within factors of 2–3). We recommend sampling for C / ²³⁴Th from a standard depth of 100 m, or at least one depth below the mixed layer using either large volume size fractionated filtration to capture the rarer large particles, or a sediment trap or other device to collect sinking particles. We also recommend collection of multiple ²³⁴Th profiles and C / ²³⁴Th samples during the course of longer observation periods to better sample temporal variations in both ²³⁴Th flux and the characteristic of sinking particles. We are encouraged by new technologies which are optimized to more reliably sample truly settling particles, and expect the utility of this tracer to increase, not just for upper ocean C fluxes but for other elements and processes deeper in the water column.     

Comparison of techniques for pre-concentrating radium from seawater

In the framework of the KEOPS project (KErguelen: compared study of the Ocean and the Plateau in Surface water), we aimed to provide information on the water mass pathways and vertical mixing on the Kerguelen Plateau, Southern Ocean, based on ²²⁸Ra profiles. Because ²²⁸Ra activities are extremely low in this area (~ 0.1 dpm/100 kg or ~ 2.10^− 18 g kg^− 1), the filtration of large volumes of seawater was required in order to be able to detect it with minimal uncertainty. This challenging study was an opportunity for us to test and compare methods aimed at removing efficiently radium isotopes from seawater. We used Mn-fiber that retains radium and that allows the measurement of all four radium isotopes (²²⁶Ra, ²²⁸Ra, ²²³Ra, ²²⁴Ra). First, we used Niskin bottles or the ship's seawater intake to collect large volumes of seawater that were passed onto Mn-fiber in the laboratory. Second, we filled cartridges with Mn-fiber that we placed in tandem on in situ pumps. Finally, we fixed nylon nets filled with Mn-fiber on the frame of in situ pumps to allow the passive filtration of seawater during the pump deployment.Yields of radium fixation on the cartridges filled with Mn-fiber and placed on in situ pumps are ca. 30% when combining the two cartridges. Because large volumes of seawater can be filtered with these pumps, this yields to effective volumes of 177–280 kg (that is, higher than that recovered from fourteen 12-l Niskin bottles). Finally, the effective volume of seawater that passed through Mn-fiber placed in nylon nets and deployed during 4 h ranged between 125 and 364 kg. Consequently, the two techniques that separate Ra isotopes in situ are good alternatives for pre-concentrating radium from seawater. They can save ship-time by avoiding repeated CTD casts to obtain the large volumes of seawater. This is especially true when in situ pumps are deployed to collect suspended particles. However, both methods only provide ²²⁸Ra/²²⁶Ra ratios. The determination of the ²²⁸Ra specific activity is obtained by multiplying this ratio by the ²²⁶Ra activity measured in a discrete sample collected at the same water depth.     

海水中228Th、234Th、228Ra的联合富集与测定

采用大体积现场泵方法同时采集不同粒级的^228Th、^234Th及溶解态的^228Th、^234Th、^228Ra．以小体积MnO2共沉淀-β计数法测定海水中的总^234Th活度（A＇TTh）；用Goflo采水器采集6～10dm^3海水，继而过滤收集颗粒物质并测定其^234Th的活度（A’PTh）；以α能谱测定分离纯化后的^228Th；对^228Ra则是采用测定其子体^228Ac的β放射性方法．采用此流程分析了南海2004年2月航次A1站住的样品，获得了较好的结果．     

海水中234Th的超低水平液闪谱仪测定

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.     

The investigation on particulate organic carbon fluxes with disequilibria between thorium-234 and uranium-238 in the Prydz Bay, the Southern Ocean

Dissolved and particulate thorium-234, particulate organic carbon in the upper 150 m of water columns from five stations in the Prydz Bay, the Southern Ocean were determined during the 22nd Chinese National Antarctic Research Expedition （from November 2005 to March 2006 ）. The disequilibria between thorium-234 and its parent uranium-238 in upper layer was used to derive the averaged residence time of thorium-234, which decreased along with the latitude to the south and a minimum value, 1 - 8 d for particulate thorium-234 and 29 - 48 d for dissolved thorium-234, appeared at the medium latitude station, and the export fluxes of thorium-234 were calculated too and ＇a maximum value, 0. 35 -0. 63 Bq/（m^3 · d） for the particulate thorium-234 and 0. 44 -0. 65 Bq/ （m^3 ·d） for the dissolved thorium-234, appeared at the same station. The export fluxes of particulate organic carbon at different water columns were derived by two methods with irreversible scavenging model, and the averaged values were 104. 7 mmol/ （ m2 · d ） （ E method） and 120. 6 mmol/（ m2·d ） （ B method ）, respectively, indicating that a relatively high new production would exist in summer in the Prydz Bay where it will play a potential significant role in sequestering the absorption CO2 to deeper ocean.     

An international intercalibration for mercury in seawater

An intercalibration between 32 laboratories in 16 countries was conducted using acidified and ultraviolet-irradiated seawater. One sample was natural seawater but two were spiked with mercuric chloride, 15.4 and 143 ngl^?1, respectively. The results show, for the majority of the laboratories, good accuracy and precision in the recovery of spikes but they also demonstrate that the most serious errors in low-level determinations are systematic.     

An intercalibration for trace metals in seawater

This paper describes the results of a recent international intercalibration experiment for trace metals in seawater. The results show that considerable improvements in analytical ability have been made for several metals at concentrations close to those found in offshore marine waters. Some systematic differences between the results of analyses of frozen and acidified samples are evident for most metals. The application of two different analytical techniques, atomic absorption spectrophotometry and anodic stripping voltammetry, appears to introduce relatively small differences in the results for copper and cadmium at near-natural concentrations.Two factors limiting our ability to conduct trace metal intercalibrations at the levels found in the deep ocean are the extent of tolerable contamination, especially for zinc and lead, and the degree to which the overall homogeneity of a group of intercalibration samples can be assured. Some reexamination of methods of sample preparation needs to be carried out before such low level calibrations can be effectively conducted.     

Some improved techniques for measuring radon and radium in marine sediments and in seawater

By careful sampling and sample processing, radon and radium may be determined in close-spaced sediment segments. These determinations permit estimation of the radon deficit in sea-floor sediments. Collecting radium on manganese-treated fiber greatly simplifies analysis of near-bottom waters. Some improved radon separation and counting techniques are described. With these methods a single operator can process four samples for radon in 140 min. Overall efficiency (extraction-transfer-counting) is 88%. Blanks are negligible. Reproducibilities of 2.6% and 3.8% are achieved for radium and radon, respectively.     

A practical method for the simultaneous determination of234Th,226Ra,210Pb and210Po in seawater

A practical method has been developed for the simultaneous determination of²²⁶Ra,²³⁴Th,²¹⁰Pb and²¹⁰Po in seawater. In the method, the samples are spiked with²²⁸Ra,²³⁰Th,²⁰⁸Po and common lead to determine chemical yield. These nuclides are coprecipitated with calcium carbonate and ferric hydroxide from 20 to 50 l of seawater and separated from one another by using coprecipitation and ion exchange techniques. Counting sources of Ra and the other nuclides are prepared by electrodeposition onto silver discs. Their radioactivities are counted with an-spectrometer and a low background-counter. This method gives a standard deviation of about 5% for replicate determination of²²⁶Ra and the other nuclides.     

MnO2共沉淀直接β计数测定小体积海水中的234Th

探讨了MnO₂共沉淀直接β计数测定小体积海水中234Th方法在固体闪烁α/β计数仪上实现的可能性,对实验流程空白、流程化学回收率、仪器探测效率、MnO₂共沉淀量对全程回收率的影响以及检测核素的特征性等进行了研究.结果表明,该方法具有稳定的流程空白和全程回收率、高的探测效率和化学回收率,且所检测核素与234Th的理论半衰期基本吻合.将该流程应用于亚热带北太平洋表层水中234Th的分析也得到了令人满意的结果.与传统方法相比,该方法具有流程简单、所用水样体积小、快速获得结果等特点,适合于船载分析,由此可实现高时空分辨率数据的获取,为海洋颗粒有机碳输出通量以及颗粒物迁移速率的研究提供了更好的分析手段.     

An improved method for the determination of ammonia in seawater

The Liddicoat, Tibbitts and Butler method for the determination of ammonia in seawater has been noticeably improved by replacing the UV lamp with a 300 VA tungsten lamp. The characteristics so achieved, a low blank value (0.012 ± 0.002a.u.), a good molar absorptivity (23.90 × 10⁻³) and a reasonably short reaction time (1 h), are such that this modified procedure is more convenient for routine work in chemical oceanography.     

An in situ pump sampler for trace materials in seawater

A battery-powdered in situ pump sampler, capable of operation at full oceanic depths, has been designed, built and tested. The pump motor, sealed in a pressure-proof housing, is coupled magnetically to the pump head. Water is drawn through a filter then passed successively through an adsorption column and the pumphead and finally through a flowmeter. The unit as a whole is pivoted and vaned so that the intake is always pointed into the current. The selectivity of the sampler depends upon the choice of packing material used in the adsorption column or columns. Column materials specific for different classes of compounds have been tested in the laboratory and at sea. Preliminary results in the collection and measurement of Cu and Cd suggest that the pumping system is free from shipboard contamination.     

Methods for intercomparison of wave measurements

The paper reviews methods for quality assessment and intercomparison of ocean wave data. The sampling variability for conventional time series recordings is summarized and compared to less common area measuring measurements. The sampling variability affects the scatter seen in simultaneous observations, and variability in excess of the sampling variability signifies real differences between the instruments. Various means of intercomparing wave parameters and spectra are discussed and two somewhat unconventional ways of deriving regression and calibration relationships are also shown. The methods are illustrated using data from SCAWVEX, focusing mainly on wave data from the HF radars and Directional Waveriders.