title: Microscale Measurement and Visualization of Sulfide δ34S Using Photographic Film Sulfide Capture Coupled with Laser Ablation Multicollector Inductively Coupled Plasma Mass Spectrometry.
abstract: Measurements of the isotopic composition of sulfate and sulfide have been essential to uncovering the microbial and geochemical processes that drive Earth's sulfur cycle. These processes routinely operate over submillimeter spatial scales in anaerobic environments, necessitating sulfur isotopic measurement techniques that can identify isotopic variability over equivalently small scales. Here we present a new method for small-scale (102μm) measurements of δ34S using black and white photographic film sulfide capture coupled with δ34S determination using laser ablation multicollector inductively coupled plasma mass spectrometry. We find that the method enables measurement of δ34S for aqueous sulfide in natural waters at high spatial resolution (<1 mm2) with reasonable accuracy (<0.9‰, 2σ) and external precision (<0.8‰, 2σ), and across an environmentally relevant concentration range (0.01-20 mmol L-1). A concentration-dependent correction is required during data analysis to achieve these specifications, which corrects δ34S measurements for mixing with sulfur native to the film material and fractionation due to Ag2S precipitation from aqueous sulfide. We demonstrate the applicability of our technique using an anaerobic incubation of seawater and sediment, mapping two-dimensional δ34Ssulfideat a 535 μm × 535 μm spatial scale, with internal precisions of 1.4‰ to 1.5‰. Our method offers the benefits of minimal sample preparation and common availability of sampling material (black and white photographic film), while retaining the necessary precision to identify sulfide δ34S variability and isotopic fractionations at high ambient sulfate and with high spatial resolutions in sulfidic environments.
authors.affiliation: Department of Earth Science and Marine Science Institute, University of California , Santa Barbara, California 93106, United States.
authors.forename: Blair M
authors.initials: BM
authors.lastname: Goodridge
authors.affiliation: Department of Earth Science and Marine Science Institute, University of California , Santa Barbara, California 93106, United States.
authors.forename: David L
authors.initials: DL
authors.lastname: Valentine