A second generation silicon isotope mass spectrometer

University Of California-Santa Barbara, Santa Barbara CA

Investigators

Abstract

This award would fund the development and purchase of a new mass spectrometer for the measurement of silicon isotope ratios in ocean samples. The field of marine silicon isotope biogeochemistry is about 20 years old having been pioneered by the lead investigator in the early 1990s. The UC Santa Barbara facility remains the only capability for such measurements in the U.S., although the field has grown to where over 18 laboratories from 8 countries are now measuring silicon isotopes in marine systems. Silicon isotopes are a powerful tool for understanding the marine silica cycle and the contribution of plankton with silica shells to marine biogeochemistry. Variations in isotopes of silicon in biogenic silica and in dissolved silicic acid are used to constrain net silica production rates in the modern ocean. Measurement of the isotopic composition of diatom frustules and of sponge spicules recovered from marine sediments are used to reconstruct the history of diatom productivity in surface waters and changes in deep water silicic acid content over geologic time. For this second-generation silicon isotope system, the investigator is partnering with Nu Instruments, Ltd. to create a commercially available instrument based on the Nu Perspective isotope ratio mass spectrometer, with a custom inlet system resulting from modifying the Nu Carb and/or the Eurovector pyrolysis inlet system(s). The two main goals for the new instrument are 1) to increase sample throughput by a factor of four and 2) to lower sample size by an order of magnitude. To meet these goals both acid and thermal decomposition of silicon fluorides to generate the analyte SiF4 gas will be explored. The second generation system should be faster, as or more precise, and much easier to use for the novice compared to the original prototype and compared to alternatives like MC-ICP-MS. Success in this development will restore routine measurements of isotopes of silicon from marine systems in the United States. By partnering with Nu Instruments, a commercial instrument will be produced that will be available to all at relatively low cost compared to competing technologies like MC-ICP-MS, contributing to national and international capacity building in this field. Finally, achieving higher sample throughput would both lower costs and facilitate the ability to make the proposed instrument available to others, further accelerating progress in the field.