QUANTIFYING PHANEROZOIC DEEP CARBON CYCLE PERTURBATIONS USING TECTONIC AND PALEOGEOGRAPHIC RECONSTRUCTIONS

Earth has avoided permanent runaway greenhouse and icehouse climate states in the past owing to the interactions between the geosphere, atmosphere, hydrosphere, and the biosphere. However, fluctuations in atmospheric carbon dioxide levels have triggered major swings between those extremes, often leading to crises and mass extinctions in the biosphere. Here we present our progress in quantifying different components of this complex system, and their role in carbon cycle perturbations.

In this presentation we explore the role of slab fluxes, orogens, large igneous provinces, carbonate platforms, and subducted carbonate sediment thicknesses in modulating atmospheric CO₂ over the Phanerozoic. We use our open-source and cross-platform GPlates software to interrogate global plate tectonic reconstructions, including the plate kinematics at subduction zones, and the interactions between subduction zones and carbonate platforms in the overriding plate. We use carbon box modelling and time-series analyses to quantify the time-evolving contribution of these processes to carbon cycling.

We propose that the Early Cretaceous greenhouse climate is likely the result of 1) a peak in the subducting plate area (leading to increased arc volcanic outgassing), 2) subsequent mantle return flow that triggered the eruption of major mantle plumes, as well as 3) the large portion of the subduction zones that were interacting with (buried) Tethyan carbonate platforms. Conversely, the overall long-term cooling since the Late Cretaceous, which leads to a Cenozoic icehouse climate, is likely a combination of enhanced silicate weathering of newly formed orogenic belts and LIPs in the near-equatorial humid belts, as well as growing seafloor carbonate sediment reservoirs that were recently quantified in other studies.

Our results highlight the importance of quantifying carbon sources and sinks controlling the planetary thermostat in the geological record. Emerging community tools that combine 4D landscape evolution, paleo-climate, and simplified components of the biosphere are also providing unprecedented insights into some of these processes, including capturing the rise and demise of massive carbonate platforms on continental margins. We believe that the integration of these different workflows and models could improve our understanding of our planet’s geological history.