Abstract
Atmospheric carbon has fluctuated considerably over geological time with solar, tectonic, and biological forcings driving changes in concentrations. However, reconstructions of past atmospheric CO2 concentrations have high uncertainties and are mostly limited to ages younger than 410 million years. To understand CO2 variations through time, complementary methods such as modelling play a key role in reconstructing past climate fluctuations.
This thesis presents the refinement of two important forcings in long-term carbon cycle models in order to test their effects on paleoclimate changes over time. Those forcings namely solid Earth degassing and consumption by silicate weathering were estimated for most of the Phanerozoic (for the last 520 Myrs). New estimates for carbon degassing were developed using two different proxies for seafloor production: subduction fluxes and arc-related zircon age distribution (reflecting continental arc-activity). The new estimates of land availability for silicate weathering were developed using refined continental flooding maps. Those maps also allowed the development of a new global sea level curve.
This thesis also presents several carbon model simulations using the new land availability and degassing estimates to calculate past atmospheric CO2 concentration over the Phanerozoic. In addition, the enigmatic Ordovician cooling was investigated using a spatially resolved climate-carbon cycle Earth system model to better understand the respective roles of paleogeography and degassing separately.