Efficient separation of boron using solid-phaseextraction for boron isotope analysis by MC-ICPMS

In nature, boron exhibits a large range of isotopic compositions (up to 150&amp;), which makes it a powerful geochemical tracer. Improving the separation and purification procedures of boron in complex matrices and at low boron contents is a challenge in obtaining high-precision and accurate boron isotope ratios. A method of ion exchange using solid-phase extraction (SPE) for the efficient separation of boron from samples with low boron contents was developed for determining boron isotopes by MC-ICP-MS. The results showed that the total amount of residual boron in the solution after ion exchange decreased from 60 mg at a vacuum pressure of 0.09 MPa to 0 at 0.04 MPa. When the vacuum pressure was between 0.008 and 0.04 MPa boron was not detected in the solution. The flow rate of the solution increased from 50 mL min 1 at a vacuum pressure of 0.008 MPa to 1358 mL min 1 at a vacuum pressure of 0.09 MPa, and the volume of eluent required increased from 300 mL at 0.008 MPa to 600 mL at 0.04 MPa. Therefore, the recommended vacuum pressure was below 0.04 MPa based on these results. The d11B values of NBS 951 after chemical treatment using SPE were between 0.25&amp; and 0.26&amp;. Using this procedure, boron in river water, rainwater and seawater samples was separated and the B isotope compositions analyzed by MC-ICP-MS. The accuracy and precision of our method were assessed by comparing the measured d11B values of these samples with published results using positive-ion thermalionization mass spectrometry. The improved efficient separation of boron from samples with a low boron content using SPE is applicable to a wide range of boron isotopic separations.</p

Controls on seasonal variations of silicate weathering and CO2 consumption in, two river catchments on the NE Tibetan Plateau

Water samples from the Buha and Shaliu Rivers, located on the semi-arid northeastern Tibetan Plateau, were collected weekly over a one year period. The major ionic compositions of water samples were measured and the daily contents of suspended particulate material (SPM) were monitored in both rivers in order to investigate the influence of lithology, climate and physical erosion on seasonal silicate weathering. In the Shaliu River, weathering of trace amounts of calcite contributes more than 50% of the ca(2+) and HCO3- to the river water. Through high-resolution variations of Ca2+ concentrations and elemental ratios, the signal of carbonate precipitation is captured at the end of monsoon in this river. The measured physical erosion rate is only 8.7-16.0 mm/kyr in this semi-arid region, which is 2-3 orders of magnitude lower than that in the Himalaya and nearby regions. In contrast with several orders of magnitude in seasonal variations of silicate weathering rates in both catchments, the distinct lithology between the catchments only leads to a 15 times difference of annual net CO2 consumption. The correlation analysis shows that seasonal silicate weathering is strongly dependent on water discharge in the semi-arid area. The most important observation is that, unrecognized by the previous studies, both physical erosion rate and air temperature exhibit two distinct trends with silicate weathering rates (and net CO2 consumption) during the years. The two trends might suggest that temperature plays a more important role on the CO2 consumption rate before the mid-monsoon under a condition of low water discharge than that after the monsoon with a high water discharge. During the period before the mid-monsoon, the relationship between temperature and silicate weathering rate exhibits higher activation energy than after the mid-monsoon, suggesting a greater dissolution of uneasily weatherable minerals from groundwater, frozen soil, and/or dust input. The relationship between erosion and weathering during the period before the mid-monsoon indicates a faster increase of silicate weathering rate, because freezing erosion produces large amount of high surface area minerals.</p

Stratigraphy and otolith microchemistry of the naked carp Gymnocypris przewalskii (Kessler) and their indication for water level of Lake Qinghai during the Ming Dynasty of China

Otoliths are biogenic carbonate minerals in the inner ear of teleost fish, whose compositions can record the physical and chemical conditions of the ambient water environment inhabited by individual fish. In this research, the fishbones and otoliths of naked carp sampled near the Bird Island, offshore Lake Qinghai, were dated and analyzed for mineralogy and microchemical compositions. Comparing the microchemical compositions of ancient otoliths with those of modern otoliths, we conclude that the ancient naked carps inhabited a relict lake formed when the lake shrank from a high lake level, by combining with the AMS-C-14 ages of fishbones and otoliths, the stratigraphy and surrounding topography of the sample site. AMS-C-14 dating results of ancient fishbones and otoliths show that these naked carps lived from 680 to 300 years ago, i.e. during the Ming Dynasty of China. The X-ray diffraction (XRD) patterns demonstrate that the ancient lapillus is composed of pure aragonite, identical to modern one, indicating that the mineral of lapillus didn&#39;t change after a long time burial and that the ancient lapillus is suitable for comparative analysis thereafter. Microchemical results show that both ratios of Mg/Ca ((70.12 +/- 18.50)x10(-5)) and delta O-18 ((1.76 +/- 1.03)parts per thousand) of ancient lapilli are significantly higher than those of modern lapilli (average Mg/Ca=(3.11 +/- 0.41)x10(-5) and delta O-18=(-4.82 +/- 0.96)parts per thousand). This reflects that the relict water body in which the ancient naked carp lived during the Ming Dynasty was characterized by higher Mg/Ca and delta O-18 ratios than modem Lake Qinghai, resulting from strong evaporation after being isolated from the main lake, similar to today&#39;s Lake Gahai. Based upon the stratigraphy and altitude of naked carp remains, it can be inferred that the altitude of lake level of Lake Qinghai reached at least 3202 m with a lake area of 4480 km(2) during the Ming Dynasty, approximately similar to 5% larger than it is today.</p

Otolith microchemistry of modern versus well-dated ancient naked carpGymnocypris przewalskii: Implication for water evolution of Lake Qinghai

There is ongoing debate over how the water level and composition of the water in Lake Qinghai changed in the past and might change in future. This study of the microchemistry of otoliths from ancient naked carp explores the chemistry of a relict lake isolated from Lake Qinghai during the Little Ice Age (LIA). A close correlation between the ages measured on fish bone and otoliths by AMS-14C, and by optically stimulated luminescence on overlying sediments, confirms a high water level in Lake Qinghai before 680–300 years ago. The contrasting compositions of the ancient otoliths relative to modern otoliths and waters indicate that the relict lake became enriched in 18O, Mg, Li, B and to a lesser extent Ba, but depleted in 13C, owing to strong evaporation, authigenic carbonates precipitation, (micro-)organism activity, and less fresh water input after it was isolated. If there were long-term fresh water input, however, a reverse trend might occur. The most important observation is that, because the waters have been supersaturated with respect to carbonates, authigenic carbonate precipitation would result in low but consistent Sr/Ca ratios in the lakes, as recorded by both the ancient and modern otoliths. The geochemical records of ancient versus modern biogenic carbonates provide insights into the long-term hydroclimatic evolution processes of an inland water body