Conspectus The reactivity and mobility of natural particles in aquatic systems have wide ranging implications for the functioning of Earth surface systems. Particles in the ocean are biologically and chemically reactive, mobile, and complex in composition. The chemical composition of marine particles is thought to be central to understanding processes that convert globally relevant elements, such as C and Fe, among forms with varying bioavailability and mobility in the ocean. The analytical tools needed to measure the complex chemistry of natural particles are the subject of this Account.We describe how a suite of complementary synchrotron radiation instruments with nano- and micrometer focusing, and X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) capabilities are changing our understanding of deep-ocean chemistry and life. Submarine venting along mid-ocean ridges creates hydrothermal plumes where dynamic particle-forming reactions occur as vent fluids mix with deep-ocean waters. Whether plumes are net sources or sinks of elements in ocean budgets depends in large part on particle formation, reactivity, and transport properties. Hydrothermal plume particles have been shown to host microbial communities and exhibit complex size distributions, aggregation behavior, and composition. X-ray microscope and microprobe instruments can address particle size and aggregation, but their true strength is in measuring chemical composition. Plume particles comprise a stunning array of inorganic and organic phases, from single-crystal sulfides to poorly ordered nanophases and polymeric organic matrices to microbial cells. X-ray microscopes and X-ray microprobes with elemental imaging, XAS, and XRD capabilities are ideal for investigating these complex materials because they can (1) measure the chemistry of organic and inorganic constituents in complex matrices, usually within the same particle or aggregate, (2) provide strong signal-to-noise data with exceedingly small amounts of material, (3) simplify the chemical complexity of particles or sets of particles with a focused-beam, providing spatial resolution over 6 orders of magnitude (nanometer to millimeter), (4) provide elemental specificity for elements in the soft-, tender-, and hard-X-ray energies, (5) switch rapidly among elements of interest, and (6) function in the presence of water and gases. Synchrotron derived data sets are discussed in the context of important advances in deep-ocean technology, sample handling and preservation, molecular microbiology, and coupled physical-chemical-biological modeling. Particle chemistry, size, and morphology are all important in determining whether particles are reactive with dissolved constituents, provide substrates for microbial respiration and growth, and are delivered to marine sediments or dispersed by deep-ocean currents.
Bibliographical noteFunding Information:
We are grateful to the following beamline scientists for leadership on micro- and nanoprobe instrument capabilities, data analysis routines, and training: Matthew Marcus, Sirine Fakra, Josep Rosell-Roque, David Kilcoyne, Tolek Tyliszczak, Martin Kunz, and Nobumichi Tamura (Advanced Light Source); Ian McNulty, David Vine, Benjamin Stripe, Matthew Newville, and Tony Lazarotti (Advanced Photon Source); and Tom Regier, Adam Gillespie, and Jay Dynes (Canadian Light Source). We thank Phoebe Lam, Sarah Nicholas, Colleen Hoffman, and Brandi Cron for contributing to sample collection and analysis. The following figure artwork was created by Dave Mottet (Associated Media Services): Figure 1; Figure 2B; filter in Figure 3; filter, vials and sample holders in Figure 4; filter in Figure 6. B.M.T., J.A.B., and G.J.D. thank the Moore Foundation (Marine Microbiology Initiative) and National Science Foundation (Ridge 2000) programs for support. C.R.G. acknowledges a Research Award of the Alexander Von Humboldt Foundation that supported preparation of this manuscript.
© 2015 American Chemical Society.