[PAOCQ] David Archer (U Chicago)

Atmospheric CO2 on geologic time scales must be regulated by some sort of climate feedback, to explain why Earth has not followed the paths of either Venus or Mars. The feedback was modeled by Berner and others as a climate-dependent rate of igneous rock weathering and carbonate production, in a spatially unresolved “box” type model. I have undertaken the project of simulating the evolution of the sedimentary rock mass through the Phanerozoic in a 1-degree gridded global representation. Plate motions are imported from files generated by GPlates, from a reconstruction by Merdith. The locations and timings of orogenic events, large igneous province eruptions, and ophiolites, were provided by Chris Scotese, and Willeit and Ganopolski provided temperature and runoff values for multiple CO2 levels in time slices of 10 myr of this reconstruction using the Potsdam CLIMBER-X model. The model runs in about a day on a laptop in Julia.

The unexpected rabbit hole has been terrestrial weathering. The standard Maher and Chamberlain model tracks the evolution of groundwater toward equilibrium according to the balance of reaction timescale versus flow-through times, a ratio called the Damkohler number. However, the presence of high levels of dissolved CO2 in river waters argues against equilibrium of CO2-consuming minerals. I will present a kinetic-based model that imagines river solutes are limited not by solubility but by overturning of the mobile regolith, the rate of which must be modulated in some way by climate. This formulation is consistent with higher solute concentrations in higher-elevation thin-soiled “weathering limited” regions than from the thick lowland “transport-limited” soils. It would explain why Huh and Edmond found higher CO2 consumption rates in Siberia than in the Amazon, due to freezing accelerating rock break-up, and the observed tight correlation between physical and chemical weathering rates. This model changes the time scale for the CO2 feedback by bringing the dynamics of the overturning regolith into the picture.

[PAOCQ] PAOC Colloquium 

Interdisciplinary seminar series that brings together the whole PAOC (Program in Atmospheres, Oceans, and Climate) community. Seminar topics include all research concerning the physics, chemistry, and biology of the atmospheres, oceans and climate, as well as talks about societal impacts of climatic processes.  

Contact: paoc-colloquium-comm@mit.edu