Controls on the Deep-Water Cycle Within Three-Dimensional Mantle Convection Models

Abstract

Earth's mantle is known to harbor water in the form of hydrous and nominally anhydrous minerals. How much water the mantle holds and whether it has remained constant through time are open questions. Previous numerical studies of the deep-water cycle have been limited to box models or 2-D calculations. Here we present for the first time results from 3-D mantle convection models. We address the evolution of the mantle's total water content by adapting a well benchmarked mantle convection code to track water, including its feedbacks on dynamics. While Earth's surface is presently covered by one ocean mass of water, our results suggest that the mantle holds approximately two ocean masses of water based on the best estimates from mineral physics. This value varies only weakly for a wide parameter space of additional complex dynamics such as viscosity laws, density controls, and phase change considerations. Our result of a mantle holding two ocean masses conforms with estimates from other branches of Earth science, suggesting that these models could be an excellent tool in understanding the spatial heterogeneity of the water found in the mantle.