Testing the silicate weathering feedback over the Phanerozoic using climate and geochemical models

Abstract:

Over geological timescales, Earth’s global mean surface temperature has been tightly regulated within the window suitable for life, despite a substantial increase in the incoming solar flux. It has long been hypothesised that this planetary homeostasis is achieved through the carbon cycle, where temperature-dependency of the silicate weathering and carbonate deposition process allows the atmospheric CO₂ reservoir to adjust to maintain a habitable surface temperature. However, it has been very difficult to find evidence of this process operating over deep time, where changes in key parameters that set weathering rates—erosion, precipitation and paleogeography —are substantial, and may undermine this proposed regulatory mechanism. I will present here an attempt to test the existence of the silciate weathering feedback by first developing a 'census' of the global silicate weathering rate over the last 400 Myrs (using HadCM3L atmosphere-ocean climate modelling linked to a surface geochemical scheme), and then comparing this to idependent estimates of the global degassing rate of CO2. If these two estimates correlate, the existence of the silicate weathering feedback is supported.