White Paper Title: 
Reactive Transport Modeling of Biogeochemical Processes at Main Endeavour Field

Reactive Transport Modeling of Biogeochemical Processes at Main Endeavour Field

B. Larson1, C. Meile1, and P. Girguis2

1University of Georgia, Department of Marine Sciences, Athens, GA 30602
2Harvard University, Department of Organismic & Evolutionary Biology, Cambridge, MA 02138 

TWG – Biogeochemical Processes – In situ bioenergetics and habitat modeling

Chemical and temperature gradients between seawater and high temperature vent fluid incident at the base of the biotic zone serve as driving forces for metabolic reactions of organisms living in this environment. Over the last decade insight into the nature of endmember and diffuse fluid composition and the biological processes that capitalize on and modify these fluids (e.g., Amend and Shock, FEMS Micro. Rev. 25: 175-243) has improved significantly. However, the spatial distribution of these processes and the linkages to surface manifestations of biology are not well constrained.

In our work, we will aim to create a reactive transport model of the Main Endeavour Field (MEF) that integrates fluid flow in porous media with chemical equilibria to predict fluid composition as a function of space and time. These predictions will then be compared to the extensive Ridge 2000 database of information on MEF fluid chemistry which in turn will enable us to provide better constraint on the transport of chemical species.

Modeling of the shallow subsurface will be undertaken with a stepwise approach that investigates transport first, followed by chemical equilibria and kinetic reaction. The initial physical and chemical characteristics of the shallow domain will be performed with Tough2 (Pruess 2004, Vadose Zone J.: 738-746), which simulates heat and mass transport in porous media at high temperatures and pressures. Subsequently, we will focus on computational descriptions of the biogeochemical processes (such as microbial primary production and carbon uptake by macrofauna) that are central to ridge hydrothermal systems.

The resulting computational framework will provide a way to test hypotheses about how perturbations to the system (such as magmatic intrusions and the aftermath thereof) affect the complex web of interdependent chemical and biological reactions to produce measurable changes in vent fluid chemistry (e.g. Lilley et al. 2003, Nature 422: 878-881; Huber et al. 2003, FEMS Micro. Eco. 43: 393-409).