The objective is to use a rapidly developing class of computer models to advance understanding of the large-scale hydrothermal systems that occur beneath the 65,000 km-long submarine system of mountain ranges referred to as mid-ocean ridges (MOR). The chemical exchange that occurs as seawater circulates through seafloor rocks affects the balance of ions in seawater and influences the carbon cycle and Earth’s climate. The resulting modifications to the ocean floor rocks also affect continental volcanism and the chemical evolution of Earth’s mantle. The proposed approach uses modern thermo-hydro-chemical modeling codes and massively parallel computation. It is a fundamentally new way to organize, interpret, and extend data that have been gathered from decades of study of MOR hydrothermal systems. The models provide a way to generalize observations into predictive tools that can be used to infer how the hydrothermal systems operate under changing conditions. This type of information is essential to the broader Earth science community. The computer modeling approach is at an early stage of development and hence benefits from special funding for exploratory research. The knowledge derived from this project will improve the ability to understand how Earth’s climate is controlled by natural processes, and why climate and ocean chemistry were different in the geologic past. The results will also enhance the capabilities of the U.S. research community for using high-performance computing to study natural Earth processes. A key part of the project is to make the approach accessible to other researchers, including students, through participation in ongoing international workshops and short courses.

In detail, the research involves adapting and developing protocols for using the Thermo-hydro-chemical (THC) code ToughReact, that has been developed over the past 40 years, to simulate the hydrothermal processes at midocean ridges. THC models explicitly couple fluid flow, heat transfer, and mineral-fluid chemical reactions, and hence can clarify the interrelationships between the many and variable parameters that affect the behavior of hydrothermal systems. The research plan involves running hundreds of simulations, with varying parameters, through a sequence of gradually increasing complexity to determine how physical characteristics (heat flux, porosity, permeability, fracture spacing, depth of circulation) and chemical characteristics (fracture and matrix mineralogy, alteration mineralogy, mineral-fluid reaction kinetics) relate to patterns of fluid chemical evolution, mineral alteration, and vent fluid compositions. The progression is to start with 2-dimensional simulations of steady state flow with chemical and mineralogical evolution proceeding for hundreds of years, the approximate time required for seafloor spreading to move the rocks a distance equal to one or two simulation grid blocks. The steady state simulations can be used to probe the main features of fluid circulation and temperature/alteration distribution for configurations representing different spreading rates, which also represent different circulation depths, lithologic structure, permeability structure, and heating profiles. The next step will be to simulate seafloor spreading in 2D, by migrating the rock matrix with its attendant temperature and mineralogy away from the ridge and adding new hot rock at the ridge axis. The results of the proposed investigation could have wide-ranging impacts in the Earth science, ocean science, planetary science, and climate science communities. In addition to producing new insights into the workings of seafloor hydrothermal systems, this project will lay groundwork for advancements in the application of modern, multi-component reactive transport simulations to broader problems in marine geology and geophysics.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

National Science Foundation (NSF)
Division of Ocean Sciences (OCE)
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Kevin Johnson
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University of California Berkeley
United States
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