Intellectual Merit: Two- and three-dimensional numerical models of phase separation and hydrothermal circulation will be developed for the Main Endeavour Field (MEF) on the Juan de Fuca Ridge. The models will integrate available vent fluid temperature, salinity, and heat flow data, along with all other relevant constraints, such as magma lens geometry and depth, extrusive layer thickness, and vent field area. A particular goal is to understand the reason for the southwest to northeast gradients in temperature and salinity across the MEF. In addition to developing a quasi-steady state circulation model that represents the behavior of the MEF between 1988 and 1995, the available data will be used to model the response of the system to the magmatic event of 1999, and what appears to be the decline in hydrothermal heat output since that time. Preliminary modeling shows that vent temperature, salinity and heat output are controlled primarily by crustal permeability distribution and the bottom boundary conditions, which control the temperature and areal extent of the two-phase zone at depth. The research program involves three inter-related tasks: (1) the development of 2-D single-pass models in order to match southwest to northeast temperature and salinity gradients across the MEF; (2) the development of 2-D models involving dike emplacement to understand the response to the 1999 event and the subsequent system decline; (3) the development of 3-D single pass single phase and two-phase models of hydrothermal circulation that includes the effect of induced circulation in layer 2A, constrained by all available heat flow data. These will be the first 2- and 3-D numerical models of phase separation for a mid-ocean ridge hydrothermal system and the first numerical models for a particular vent field that are constrained by time series data of vent temperature, hydrothermal heat output, and vent salinity. These will also be the first fully numerical models of phase separation and hydrothermal circulation of a NaCl-H2O fluid near a dike. Finally, the results will provide important insights into how a major hydrothermal system decays in time. The results of this modeling will thus provide important insights into the process of phase separation in seafloor hydrothermal systems and provide constraints on the permeability structure of the ridge axis. The results will help determine whether the decay of hydrothermal heat output is controlled by magmatic crystallization and cooling at depth or by the evolution of crustal permeability.

Broader Impacts: Although these models will be specific to the MEF, the results will lead to increased understanding of phase separation and hydrothermal circulation at mid-ocean ridges, which is a broad field of interdisciplinary study. The development of the 3D two-phase code FISHES will become an important community tool for hydrothermal modeling. The 2-D and 3-D versions of FISHES, and a user's manual, will be placed on the PIs' personal websites when they are available for general use. This research will train a new graduate female student in an important area of interdisciplinary research and train the student in the use of numerical codes. The research will also advance the scientific development of a young female researcher. The results of this research will be incorporated into courses on fluid processes taught at the university level.

National Science Foundation (NSF)
Division of Ocean Sciences (OCE)
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Bilal U. Haq
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University of Chicago
United States
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