NSF RIDGE 2000 Postdoctoral Fellowship: Development of Raman spectroscopy for in situ quantification and speciation of hydrothermal Fe and Mn particulates and sediments

Woods Hole Oceanographic Institution, Woods Hole MA

Investigators

Abstract

White (0550331) Intellectual Merit The hydrothermal flux of reduced Fe and Mn has important implications for global seawater chemistry and chemosynthetic vent biology. When Fe and Mn enriched hydrothermal fluid mixes with seawater, polymetallic sulfides precipitate and seawater trace elements are scavenged onto Fe and Mn oxyhydroxides. These processes are important because approximately 10,000 liters of deep-ocean seawater are entrained with every liter of venting hydrothermal fluid. Thus, the equivalent of the entire ocean volume is exposed to co-precipitation reactions with polymetallic sulfides and Fe-Mn oxyhydroxides on timescales that are similar to global thermohaline circulation. In addition to their role as chemical scavengers, the oxidation of both Fe(II) and Mn(II) are important energy sources for chemosynthetic microbial communities in the water column as well as at the seafloor. This research aims to develop Laser Raman spectroscopy as a means to measure the in situ chemical speciation of metal-charged hydrothermal vent fluids emanating from the seafloor. The work involves an instrument engineering effort and ground truthing the technique with laboratory experiments. All experiments will use a laboratory model laser Raman spectrometer with a remote probe head and microscope attachment. High and low temperature/ high-pressure optical cells capable of 300 C and 400 bar will be used to simulate deep-sea hydrothermal conditions. Hydrothermal sediments and plume particulates will be mineralogically characterized using X-ray diffraction and X-ray fluorescence spectrometry and then used as natural mineral assemblages for the laboratory. Broader Impacts This research provides research support for a early career female scientist and training of a postdoc at the Woods Hole Oceanographic Institution in Massachusetts. The work will develop new in situ chemical sensors of important metal species for hydrothermal vent studies. The resulting instrument would be an obvious addition to any long-term mid-ocean ridge observatory and could be modified to broadcast in situ chemical data to researchers and the public alike. To disseminate information to the public, students, and the greater oceanographic community, a website on the Chemical Sensor work will be augmented to include one on Raman spectroscopy instrumentation and hydrothermal vent applications.