Although hydrothermal plumes, over time, have had a significant impact on ocean chemistry, much remains unknown about the chemical and biological processes that occur in rising vent plumes where most mineral precipitation and redox chemistry occurs. This research addresses the abiotic and biological factors in early-stage hydrothermal vent plume processes and the impacts of these processes on particle formation, microbial community composition and structure, and chemical scavenging and transport by both organic material and mineral precipitates. Vent fluids, associated precipitated minerals and microbial samples that were collected on a cruise to the Eastern Lau Spreading Center in 2009 will be analyzed using state-of-the-art mineralogical and molecular biological techniques. These include synchrotron radiation X-ray adsorption and diffraction using the Advanced Light Source in Berkeley and metagenomics. Goals of the research are to determine the microbiological communities inhabiting the rising plumes, the role of plume-living/generated microbes and organic matter in particle formation and aggregation, chemical trends in plume chemistry from the vent to the top of the plume and its influence on the distribution of microbial species, and if particle aggregates influence the subsequent chemical evolution and fate of the particles. Models of mineralogical and biological interactions will be developed and coupled with those simulating hydrodynamics of the rising plume in order to simulate vent plume processes. Broader impacts of the work include support of three early career scientists, one of whom is from a gender under-represented in the sciences. The integration of teaching and learning which includes incorporating research into classes and working to include results into a summer camp for high school students and teachers. Two undergraduate summer students from under-represented minorities will also be involved in the research.
The goal of this collaborative research was to determine the geochemical food sources for deep-sea hydrothermal vent ecosystems. Hydrothermal vent ecosystems are different from the aquatic habitats we tend to interact with on a daily basis, such as lakes, rivers, and estuaries. Hydrothermal vent organisms must live with extremes of pressure and temperature, and make use of surprising food sources—inorganic materials derived from rocks and minerals. Although deep-sea hydrothermal vent ecosystems are novel to us, they are not rare. In fact, they are common features of a 60,000 km volcanic mountain range that spans the seafloor of every major ocean basin on the planet, known as the global mid-ocean ridge. Processes that occur in hydrothermal systems, therefore, can tell us a lot about the widespread but rarely seen diversity of life on our planet. In this project, my research group at the University of Minnesota was responsible for measuring the chemistry of particles forming in the rising hydrothermal plumes of the Eastern Lau Spreading Center. These data were shared with our collaborators to help with validation of geochemical modeling and microbial activity observations. The Eastern Lau Spreading Center was chosen as our field site because the chemistry of these vents changes a lot over a relatively short distance. We studied the rising portion of hydrothermal plumes because we think that important chemical reactions are happening in the rising plume, but this portion of hydrothermal plumes is poorly understood because it has been very difficult to sample with existing equipment. My collaborator, Chip Breier from Woods Hole Oceanographic Institution, designed special sampling equipment that made this study possible. We used this approach to collect samples for both chemical and microbiological analysis, and to answer some of our scientific questions: What chemical substrates are available to microorganisms in the plume and where do they come from? How does the chemistry of particles change as they travel through the rising plume? Is there organic carbon available to microorganisms in plume particles? We found that there is a variety of sulfur- and iron-bearing particles that can act as energy sources for microorganisms. We also discovered that Lau plumes have much less organic matter than other systems we have studied, but did detect microbial communities containing both chemosynthetic and heterotrophic organisms. This finding tells us that these communities have the potential to both produce and consume organic matter. The microbial communities in the plume were mixtures of seafloor and water column sources. While the plume particles also have a seafloor source, most of the particles are formed by new chemical reactions between vent fluids and seawater. Our data indicate that plume chemistry varies across the hydrothermal fields of the Lau Basin, as does plume microbial community composition. These trends suggest to us that the vent chemistry is an important factor for plume microbial community composition. However, our analyses to-date point to the physical oceanography of the Lau as a critical constraint on microbial community composition as it controls the mixing of source fluids. This project answered many questions concerning hydrothermal plume chemistry and microbiology and their role in marine biogeochemical cycles. In the process, it has also furthered the education and careers of a total of 7 undergraduate, graduate, and postdoctoral students at Woods Hole Oceanographic Institution, Cambridge University, Stanford University, the University of Minnesota-Twin Cities, and the University of Michigan-Ann Arbor.
