Using Monte Carlo Analysis and Present-Day Constraints on Earth's Water Budget to Produce Feasible Water and Thermal Histories via Reverse-Time Integration
Abstract
Earth is a unique planet in our solar system in that it has a large, stable, and directly observable body of water on its surface. Earth's surface ocean volume is controlled by fluxes of water into its interior (subduction zones) and out of its interior (mid-ocean ridges), however it is not entirely clear how this system self-regulates or stabilizes over time. This deep water cycling also affects Earth's thermal evolution, as water content modulates mantle viscosity and the solidus. It follows that reproducing the thermal evolution of Earth's mantle requires a knowledge of the mantle water content and the net flux of water into and out of Earth's interior, yet these parameters are not well-known. In order to tackle this problem, this work seeks to use a Monte Carlo modeling analysis to find the present-day parameter space for water content and net rate of regassing or degassing that allows for a stable co-dependent water and thermal evolution backwards in time. Preliminary results suggest that, as the models develop in the reverse time direction, feedbacks can easily drive the system to unrealistic states where all water is regassed back into the mantle or all water is degassed to the surface; only a small subset of models allow both surface and mantle water to exist back through Earth's history. Best solutions to the models occur when the net flux of water into the mantle at the present day is ~1011-1012 kg yr-1. Models that start with a smaller net influx or a net outflux quickly move all the water on Earth's surface into its mantle through a positive feedback process between viscosity and Earth's heat budget, while models that start with a larger net influx tend to move all the water in Earth's mantle to its surface for the same reasons. Models where viscosity is only dependent on temperature reach states where the mantle is complete dry or "saturated" less rapidly than when viscosity is a function of water concentration and temperature, but do not fully characterize the temperature and water dependencies involved in viscosity. These models will ultimately help constrain Earth's present-day water budget and net rate of regassing or degassing.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMDI0110001T
- Keywords:
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- 3344 Paleoclimatology;
- ATMOSPHERIC PROCESSES;
- 0545 Modeling;
- COMPUTATIONAL GEOPHYSICS;
- 1038 Mantle processes;
- GEOCHEMISTRY;
- 8147 Planetary interiors;
- TECTONOPHYSICS