CHIP BREIER: GEOCHEMISTRY & ENVIRONMENTAL ROBOTICS

Lau Basin


NSF RIDGE2000 1038055: Collaborative Research: Integrating Geochemistry, Microbiology, and Hydrodynamics: A Model for Trace Element Transport and Fate in Hydrothermal Plumes

Public data available here. Prepublic data for collaborators available here.

The goal of this research is to understand the role of seafloor hydrothermal venting on nutrient concentrations and microbial community composition in the modern ocean and ultimately through geologic time. The environment at deep-sea hydrothermal vents is extremely different from the environment we know. Extremes of pressure, temperature, and chemistry make deep-sea vent systems excellent sites to study how ocean life processes respond to environmental disturbance, take advantage of chemical energy derived from ocean crust, and influence Earth’s chemistry as a whole. The latter is possible. Though deep-sea hydrothermal vent systems are novel to us, they are not rare. They are common features of the mid-ocean ridge system and submarine volcanoes, which are widely dispersed through the oceans. Processes that occur in hydrothermal systems, therefore, have global consequences.

In this project, we specifically studied the chemistry and microbiology of the rising hydrothermal plumes of the Eastern Lau Spreading Center in the south Pacific. This location was chosen because the chemistry of these vents is especially diverse. We studied the rising portion of hydrothermal plumes because this is where chemistry changes most rapidly. This portion of hydrothermal plumes is also the hardest to sample. It rises vertically from the seafloor like smoke from a chimney. As a result, the only way to systematically sample this environment is with a deep-sea vehicle and specialized sampling equipment, which we developed. We used this approach to collect samples for both chemical and microbiological analysis. We analyzed those samples to determine their chemistry and mineralogy and their microbial community composition. We used this data to answer a number of scientific hypotheses associated with these overarching questions:

To what extent does organic material influence the reactivity and transport properties of the mineral component of hydrothermal plumes? What is the origin of organic material in hydrothermal plumes?

What is the nature and source of the microorganisms found in hydrothermal plumes? How does the structure and function of plume microbial communities vary as (i) plumes rise, age, and mix with seawater and (ii) between plumes of varying initial chemistry?

We found that there is great variation in the relative amount of organic matter in hydrothermal plumes. Lau plumes, in fact, exhibit much less organic matter than other systems we have studied. Our evidence suggests multiple sources and means for organic matter incorporation. We also found an active plume microbial community containing both chemosynthetic and heterotrophic organisms; thus these communities have the potential to both produce and consume organic matter. These plume communities are a mixture of seafloor vent community microorganisms and those found in the water column. Our data also indicate that plume chemistry varies across the hydrothermal fields of the Lau Basin, as does plume microbial community composition. The latter suggests a potential geochemical driver for plume microbial community composition. However plume physics also places a critical constraint on 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 geochemical 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.