Intellectual merit. This proposal requests funding for acollaborative experimental and analytical study of global recycling of sulfur based on the isotopic fractionation between S-bearing gases, silicate melt, and condensed S phases (sulfate and sulfide). Scientists from three institutions are involved (American Museum of Natural History (C. Mandeville, lead PI), Woods Hole Oceanographic Institution (N. Shimizu, PI), and University of Rhode Island (K. Kelley, PI). The proposed research comprises two separate aspects. First, laboratory experiments will be carried out to determine mechanisms and magnitudes of S isotopic fractionations between coexisting phases as a function of pressure, temperature, chemical composition of silicate melt, fugacity of oxygen, and speciation of S in silicate melt and gas phase. S isotopic analysis will be made using secondary ion mass spectrometry (SIMS) techniques with the IMS 1280 ion microprobe at Woods Hole Oceanographic Institution. This new SIMS technique for sulfur isotopic measurements can now be applied to silicate glasses at the melt inclusion (10's of microns) scale thus allowing analysis of sulfur isotopes in trapped magma inclusions, evaluation of volcanic degassing, and assessment of the ultimate source of sulfur in arc magmas. In a second phase, S isotopic compositions will be determined for natural primitive magmas trapped as glass inclusions hosted by olivine, orthopyroxene and clinopyroxene; complementary volatile, lithophile and high field strength trace element abundances will be determined on the same glasses via laser ablation ICP-MS analysis at Rhode Island. This will be carried out for samples from Galunggung (Indonesia), Etna (Italy), and Augustine (Alaska), volcanoes so as to investigate S isotopic compositions of source mantle, effects of water and oxygen fugacity on S isotopic fractionation between silicate melt and S-bearing phases, and effects of degassing processes on S isotopic composition of silicate melts. Together, these research paths are expected to establish routine measurement of S isotope geochemistry as a powerful tracer for chemical fluxes across subduction zones and for assessment of sulfur recycling among Earth's major reservoirs (mantle, lithosphere (including crust), and coupled hydrosphere-atmosphere).
Broader Impacts. Understanding of volatile degassing is central to monitoring and forecasting volcanic eruptions. Also. improved understanding of sulfur isotope geochemistry is vital to volcanic hazard mitigation. The PIs will incorporate the scientific results into educational and outreach programs at their respective institutions. PI Kelley is an early-career female scientist, supported by the University of Rhode Island's NSF-funded ADVANCE program, which is aimed at nurturing the careers of female scientists. She will advise a Summer Undergraduate Research Fellowship in Oceanography (SURFO) student (Univ. of Rhode Island, Graduate School of Oceanography's NSF-funded REU program) under the umbrella of this project. PI Mandeville will advise two American Museum of Natural History REU students in years 2 and 3 of this project. The PI will participate as a lecturer in the Training Renewal for Urban Science Teaching (TRUST) program at AMNH which provides professional development opportunities for greater New York City high school Earth science teachers. A TRUST session will be administered by AMNH in each year of the project.
