Chuan-Hsiung Chung

Precise determination of triple Sr isotopes (δ87Sr and δ88Sr) using MC-ICP-MS

The non-traditional stable strontium (Sr) isotopes have received increasing attention recently as new geochemical tracers for studying Sr isotopic fractionation and source identification. This has been attributed to the advancement in multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS), allows to determine precisely and simultaneously of the triple Sr isotopes. In this study, we applied a modified empirical external normalization (EEN) MC-ICPMS procedure for mass bias correction in Sr isotopic measurement using (92)Zr/(90)Zr. High-purity Zr Standard was spiked into sample solutions and the degree of fractionation was calculated off-line using an exponential law. The long-term external reproducibility for NIST SRM 987 δ(87)Sr and δ(88)Sr was better than 0.040‰ and 0.018‰ (2SD), respectively. The IAPSO standard seawater was used as a secondary standard to validate the analytical protocol and the absolute ratios measured were 0.709161±0.000018 for (87)Sr/(86)Sr, 0.177±0.021‰ for δ(87)Sr, and 0.370±0.026‰ for δ(88)Sr (2SD, n=7). These values are in good agreement with the literature data analyzed by thermal ionization mass spectrometry (TIMS) double spike technique. Rock standards, BHVO-2, BCR-2 and AGV-2 were also analyzed to validate the robustness of the methodology and showed identical results with literature data. Compared to previous (91)Zr/(90)Zr correction, we obtained improved results based on (92)Zr/(90)Zr, probably due to similar mass difference between (92)Zr/(90)Zr and measured Sr isotopes. The new analytical protocol presented in this study not only improves the analytical precision but also increases sample efficiency by omitting the use of the standard-sample bracketing (SSB) procedure.

Application of an improved ion exchange technique for the measurement of δ34S values from microgram quantities of sulfur by MC-ICPMS

Motivated by limitations of the existing solution-based Multiple Collector Inductively Coupled Plasma Mass Spectrometry (MC-ICPMS) studies to low sulfur concentrations, analytical procedures are reported for δ34S measurements (2σ precision of 0.24–0.34‰) at sulfur concentration [S] of 2 μg mL−1, following its purification by anion exchange resin (AER). δ34S values of International Atomic Energy Agency (IAEA) standards S-1, S-2 and S-3, and IAPSO seawater measured in this study agree (within uncertainties) with the consensus values measured by conventional techniques. These values also are in close agreement with the reported numbers by an MC-ICPMS study in which δ34S was measured at [S] of 20 μg mL−1 following its purification by cation exchange resin (CER). Anion exchange purification offers significant advantages of less sample requirement (2 μg S vs. 500 μg S), lower procedural blanks (∼12 ng vs. ∼250 ng of S), and less chemical requirements and sample processing times, over the cation exchange; therefore, δ34S measurements attempted in this study would suffer significantly from procedural blank if CER is used. It is believed that the procedures reported in this study would establish the application of MC-ICPMS to δ34S measurements in low sulfur containing samples, and should find widespread application especially in studies related to glacier, snow, rainwater and aerosol samples.

Nonhomogeneous seawater Sr isotopic composition in the coastal oceans: A novel tool for tracing water masses and submarine groundwater discharge

Here we present high-precision (2σ = ±3 ppm) 87Sr/86Sr measurements in coastal waters, together with salinity, to evaluate water mass mixing and the influence of submarine groundwater discharge (SGD) in coastal waters and marginal seas. Nonhomogeneous Sr isotopic variations in water columns were documented in the Southern Okinawa Trough (SOT), South China Sea, and Kao-ping Canyon (KPC), where seawater 87Sr/86Sr varied up to 70 ppm. Seawater Sr isotopic composition changes only slightly in the upper 200 m of the SOT but was detectable and highly correlated with salinity, indicating a mixing between radiogenic North Pacific Tropical Water (high 87Sr/86Sr and high salinity) at 100–150 m and a less radiogenic component with low 87Sr/86Sr and low salinity at ∼200 m. Vertical profiles of seawater 87Sr/86Sr along the KPC show significant variations, suggesting dynamic mixing affected by continental inputs (i.e., river runoff and SGD) in this region. These results highlight the potential use of seawater Sr isotopes as a powerful tracer for determining mixing ratios and the dynamic mixing of oceanic water masses, especially in coastal and marginal seas.

Riverine lithium isotope systematic during continental weathering from an active orogenic belt, Taiwan

HCl molecules emitted from volcanoes breakdown to form chlorine free radicals via heterogeneous chemical reactions and photolysis, which act as catalysts to the breakdown of ozone in the stratosphere. Ozone depletion of up to 2-7% was estimated following the Pinatubo 1991 eruption [1]. However, only stratospheric HCl is dangerous to ozone, and the amount of HCl that reaches these levels is often lower than expected [2]. This suggests that HCl is removed from the eruption column at tropospheric levels. Previously suggested mechanisms include inclusion of HCl into supercooled droplets or ice crystals [3]. In order to investigate the removal of HCl from the atmosphere by adsorption onto ash in volcanic plumes, glass with the composition of the Pinatubo 1991 dacite [4] was synthesised and ground to ash-sized particles using a planetary mill. The ash was then placed in a simple volumetric vacuum device, which was purged with HCl gas to a desired pressure. The ash was connected to the system and the adsorption of HCl onto the ash surface recorded by the resulting pressure drop until an equilibrium pressure was reached. Preliminary results from experimental runs beginning with an HCl gas pressure of 31 mbar, 100 mbar, 250 mbar, 504 mbar and 975 mbar indicate that adsorption on the order of 0.5 mgm-2 occurs even at low partial pressures of HCl. [1] Robock (2000) Rev. Geophys. 38, 191-219. [2] Oppenheimer (2003) In Treatise on Geochemistry. [3] Textor et al. (2003) Geol Soc Lon Spec Pub 213, 307-328. [4] Scaillet & Evans (1999) J. Petr. 40, 381-411