High Precision Determination of 48Ca/42Ca Ratio by TIMS for Ca Isotope Fractionation Studies

For studies of mass-dependent fractionation of calcium isotopes in natural materials, the ⁴⁸Ca/⁴²Ca ratio is a superior choice to the conventionally measured ⁴⁴Ca/⁴⁰Ca ratio for two important reasons. These are (1) mass-dependent fractionation can be determined free from the effects of inherited or ingrown radiogenic ⁴⁰Ca and (2) this ratio increases the spread of measured isotopic masses by 50%, resulting in statistically better resolution of fractionation, assuming similar precision. A third, though strictly technical, advantage is the inherent ability of a mass spectrometer to measure ratios close to unity (⁴⁸Ca/⁴²Ca) more precisely than very small or large ratios (⁴⁴Ca/⁴⁰Ca). However, because of the very low natural abundance of both ⁴⁸Ca and ⁴²Ca, their ratio has been very difficult to measure, the only attempt so far being on a high mass resolution MC-ICP-MS with a precision of 0.33%. We report here determination of the ⁴⁸Ca/⁴²Ca ratio by the more commonly available and user-friendly multi-collector TIMS using a ⁴³Ca-⁴⁶Ca double-spike, with a significantly better precision of 0.18% (2s). The ⁴⁸Ca/⁴⁰Ca or ⁴⁴Ca/⁴⁰Ca ratio can also be measured in the same mass spectrometer run to provide complementary information on any radiogenic component.     

Intensified mid-Holocene Asian monsoon recorded in corals from Kikai Island, subtropical northwestern Pacific

Coupled records of Sr/Ca and oxygen isotope ratios (δ¹⁸O) of coral skeletons have been used to produce quantitative estimates of paleo-sea surface temperature (SST) and δ¹⁸O of surface seawater that can in some cases be converted to sea surface salinity (SSS). Two fossil corals from Kikai Island in the subtropical northwestern Pacific, a location affected by East Asian summer and winter monsoons, were analyzed to investigate differences between mid-Holocene and present-day SST and SSS. At 6180 cal yr BP, SSTs were roughly the same as today, both in summer and winter; δ¹⁸O_seawater and SSS values were higher both in summer (+ 0.5‰, +1.1 psu) and in winter (+ 0.2‰, + 0.6 psu) than modern values. At 7010 cal yr BP, SSTs were slightly cooler both in summer and winter (−0.8 and −0.6 °C), whereas δ¹⁸O_seawater and SSS had higher values in summer (+ 0.3‰, + 0.6 psu) and in winter (+ 0.8‰, + 1.9 psu) than present-day values. These results are consistent with other marine records for the mid-Holocene of the low and midlatitudes in the northwestern Pacific. Such regional conditions indicate that the East Asian summer and winter monsoons were more intense in the mid-Holocene, which was likely a function of the mid-Holocene insolation regime.     

Studies on Quantity and Intensity of Potassium in Some Taiwan Farmland Soils

Potassium (K) is one of the major nutritions for plants. The evaluation of K quantity and intensity relationships (K Q/I curve) in different farmland soils is important for the appropriate application of K fertilizer. With this information the pollution of K fertilizer in the environment can be prevented. Potassium ions in solution and in exchange complex are available to plants. However, the K availability is affected by the antagonism of Ca and Mg ions. The K quantity–intensity relationships (K Q/I curve) has been suggested to describe the K availability in soil, taking into account the competition between K ions and Ca and Mg ions for exchange sites on the soil exchange complex. In this experiment, we studied the Q/I plot of the soils and found that the parameters can be used to evaluate the supply state of K. The results show that the K Q/I relationships of the five soils differed as the Ca concentration of the initial solution is varied. This phenomenon reflected different degrees of exchange of K by Ca on the exchangeable sites of the clay minerals. The intensity of the potassium supply of Nieuniaokang and Erling soils possessed higher AR⁰ values, indicating that exchangeable K in these soils are primarily on the plannar surface of the clay particles; while those of the Liuying, Shanghua, and Taikang series are primarily on the crystal edge surfaces and are less available to the plant. The K supply intensity of Chiangjung soil is lower when the Ca concentration is low, but it increased when the Ca concentration is high, and the K supply intensity of Pinchen soil is the opposite. The K supply intensity of Nieuniaokang soil is high, but its potential buffering capacity (PBC) is low. Therefore, it is suggested that the K application should be split into small doses to maintain a high K supply intensity. The K supply intensity of Liuying soil is low, but its PBC is large, so it is expected that a large amount of K fertilizers would be needed to increase the K supply intensity to a more available level. The supply intensity and the buffering capacity of the Chiangjung and Pinchen soils are low, and the K management in these soils will be more difficult.     

Late Quaternary palaeohydrological changes in the large playa Lake Frome in central Australia, recorded from the Mg/Ca and Sr/Ca in ostracod valves and biotic remains

The last 42,000 years of hydrological history of Lake Frome, a large playa located in the arid part of northern South Australia, which is hypersaline and most often dry today, is reconstructed using a combination of ostracod assemblages, other microfossil remains, and the trace elemental composition of the selected halobiont ostracod species of Diacypris and Reticypris.The Mg/Ca and Sr/Ca of ostracod valves from 2 cores relate to significant hydrological changes that affected the lake over time. The reconstruction of the Sr/Ca of the lake’s waters, based on the Sr/Ca of ostracod shells, shows that when the lake fills the waters originate mostly from runoff, not from hypersaline waters located below the lake or the surrounding aquifers. The Last Glacial Maximum saw gypsum deflation from the lake.Prior to 25K yBP, Frome had a stable hydrological regime, permanent water and low salinities, with occasional freshwater conditions between 42 and 33K yBP. From 25 to 20.3K yBP, salinities fluctuated and ephemeral conditions operated. After that, until ∼14.8K yBP, a brine pool was located below the lake and was therefore under a different hydrological regime. Between 13 and 11.2K yBP, wet conditions occurred, but such conditions were not seen again during the Holocene.     

Sr/Ca,Mg/Ca:珊瑚岛鸟粪沉积的物源指示计*

文章尝试用Sr/Ca,Mg/Ca比值作物源指示计,区分了珊瑚岛屿受到海鸟粪影响的湖泊沉积物中鸟粪、珊瑚砂、植物这几种主要的环境介质对沉积物的相对贡献,据此恢复1800年来西沙群岛东岛海鸟数量变化和植被演化的历史。结果表明,东岛海鸟数量的变化历史可划分为潜伏期、增长期、稳定期和衰退期4个阶段,历史时期东岛海鸟生态系统的建立和发展与岛屿植被的演变有着密切的联系。研究获得的方法和初步结论为进一步开展西沙岛屿海鸟数量变化、植被演化的广泛对比并探讨与气候变化、人类活动的相互联系提供了基础。     

华北中元古代浅海碳酸盐沉淀方式变化:海水氧化还原条件波动的响应?*

海相碳酸盐的沉淀方式被认为与水体氧化还原条件密切相关,即太古宙至古元古代缺氧的铁化海水中碳酸盐沉淀抑制剂Fe²⁺和Mn²⁺强力抑制灰泥在水柱中成核,但允许文石直接在海底生长,从而导致大量文石以海底沉淀方式产出,而新元古代适度的氧化海水则有利于灰泥以水柱沉淀方式形成。然而,碳酸盐沉淀方式的长期变化还可能受控于其他因素,其与海水氧化还原条件之间的关系还需要通过大量具体实例来验证。针对上述科学问题,笔者选择碳酸盐沉淀方式尚处于过渡时期的华北中元古界碳酸盐岩为研究对象,开展碳酸盐沉淀方式及与之对应的氧化还原条件研究。结果表明,华北高于庄组三段(约1.56 Ga)、雾迷山组四段下部(约1.48 Ga)和铁岭组二段(约1.44 Ga)发育大量灰泥水柱沉淀,其Ⅰ/(Ca+Mg)值较高(普遍大于0.5 μmol/mol)、Ce负异常(低至0.8),指示适度氧化的条件;而高于庄组四段下部(约1.55 Ga)和雾迷山组二段中部(约1.50 Ga)则发育大量纤维状文石海底沉淀,其Ⅰ/(Ca+Mg)值约为0,指示次氧化至缺氧的环境。因此,本研究首次用大量实例证实了前寒武纪海水氧化还原条件对碳酸盐沉淀方式的重要调控作用,并且后者可作为海水氧化还原条件分析的重要指标,适用于高效开展长序列、多剖面的低氧背景下前寒武纪碳酸盐岩地层的氧化还原条件分析。     

Geochemical signal of seasonality in annually laminated organic- carbonate sediments in Shira lake(Khakasia)

正1 Introduction The most valuable for the task of climate reconstruction are the time series with an annual resolution,which allows to reveal natural periodicity and pass to the search for mechanisms of regional and global climatic changes.Bottom sediments of lakes are one of the best climate archives in addition to tree ring series,ice cores etc.     

Siderophile elements in chondrules of CV chondrites

New bulk compositional data for 34 Allende chondrules are presented. Whole chondrules were analyzed by instrumental neutron activation analysis (INAA). The new data set is evaluated together with older INAA data on Allende chondrules and recent INAA data on Mokoia chondrules. The Ni/Co ratios of 200 chondrules are close to the CI- or solar ratio. The chondritic Ni/Co ratios require an unfractionated chondritic metal source and set a limit to the fraction of metal lost from molten chondrules. The bulk chondrule Fe/Ni and Fe/Co ratios are more variable but on average chondritic. Iridium and other refractory metals have extremely variable concentrations in chondrules. High Ir chondrules have chondritic Ir/Sc ratios. They are dominated by CAI (Ca,Al-rich inclusion) components. Low Ir chondrules have approximately chondritic Ir/Ni ratios reflecting mixing with chondritic metal. In low Ir chondrules Ir correlates and in high Ir chondrules Ir does not correlate with Ni or Co. A large fraction of Ir may have entered chondrules in variable amounts as tiny grains of refractory metal alloys.Most Allende chondrules have Ir/Sc ratios below bulk meteorite ratios. Matrix must have a complementary high Ir/Sc ratio, as bulk Allende has approximately chondritic Ir/Sc ratio. Similarly, the high average Ir/Ni ratios of Allende chondrules must be balanced by low Ir/Ni ratios in matrix to obtain the bulk Allende Ir/Ni ratio, which is close to the average solar system ratio.More recent data on single chondrules from Allende by ICP-MS (Inductively Coupled Plasma Mass Spectrometry) and ICP-OES (Inductively Coupled Optical Emission Spectrometry) show the same trends as the INAA data discussed here.     

Using LA-ICP-MS to analysis elemental composition of statoliths of Scyphozoan jellyfish

Scyphozoan jellyfish outbreak events are drawing increasing attentions during the past decade. Elemental compositions of statoliths are helpful to understand jellyfish life history and blooming mechanisms, but very rare endeavor has been focused on the Scyphozoan class. In this work, we explored the feasibility of element analysis of Aurelia aurita (a representative Scyphozoan jellyfish outbreak species in China) which may be used as proxies of environment parameters during jellyfish living and moving. Statolith crystals of Aurelia aurita were found to be a gathering of hexahedron type trigonal needle with size of 10?50 μm long, and 5?10 μm in diameter. By using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) downhole profiling method, elements such as Ca, Sr, Mg, Na and P were found to be above the limit of detection and limit of quantification. The epidermis of statocyst could significantly impact the element analyses, so the real statolith element signal section needs to be selected based on elements and Ca profiles together with care. By laser ablated a signal spot repeatedly, the analytical uncertainty was about 3%?4% for Sr/Ca content ratio and Mg/Ca content ratio, but above 10% for other element/Ca content ratios (n=3). Based on the analysis of statolith from temperature-control cultured jellyfish, Sr/Ca content ratios among different statoliths of the same jellyfish were about 6% (n=14), demonstrating biological processes/vital effects causing small variations compared with analytical uncertainties. Therefore, Sr/Ca content ratios may be used as a potential proxy to reveal the living environment variations the Scyphozoan jellyfish has experienced, such as temperature history, which is helpful to understand jellyfish bloom mechanisms.     

海洋沉积物中酸溶硫化物对二价金属镉的地球化学特征及生物毒性的影响

通过海洋沉积物镉加标实验、沉积物间隙水分析和对加标沉积物毒性的10天底栖端足类生物检验，重点探讨在硫化物存在条件下，二介有毒金属镉在沉积物－间隙水系统中的地球化学分配和化学活性，及镉在沉积物中的化学活性与生物毒性间的关系。研究结果表明，镉加标沉积物的毒性与间隙水中镉浓度呈正相关，而与沉积物镉总量无关。在硫化物存在条件下，沉积物－间隙水系统中，二价镉在固、液两相同的分配主要受酸溶硫化物（AVS）影响。AVS归一化沉积物中二价镉含量可作为预测和评价二价有毒金属镉的化学分配行为和生物可获性或毒性的有效方法。酸解硫化物时同步提取的金融镉SEMCd^2 与AVS的摩尔浓度之比[SEMCd^2 ]/[AVS]可用作评价缺氧状况下镉沾污沉积物的环境质量和毒性的判据。