Tectonic drivers of the planetary carbon cycle

Plate tectonics forms an essential component of the life support system on our planet. Plate tectonic processes facilitate the release of carbon dioxide (CO2) into the atmosphere, while ensuring that a runaway greenhouse effect (such as that operating on Venus) is unlikely to develop through tectonic CO2 drawn-down mechanisms. Past attempts at quantifying tectonic fluxes of CO2 have relied on proxies, such as inverting sea level curves. Here we present work through the Deep Carbon Observatory that forms the first attempt to quantify major components of the tectonic fluxes of carbon using the latest plate tectonic reconstructions developed in the open-source and cross-platform GPlates (www.gplates.org ) software. We have explored the role of subduction zone lengths, subducting plate area, continental rift and mid-oceanic ridge lengths, magmatic decarbonation of carbonate platforms, and the eruption of Large Igneous Provinces (LIPs) on the release of CO2 since the assembly and dispersal of the Pangea supercontinent in the last ~250 million years. We have also attempted to quantify the tectonic carbon sequestration related to silicate weathering of orogens, ophiolites, and LIPs, as well as the modulating role of the biosphere with the evolution of marine calcifiers since ~200 Ma. Our analysis suggests that major geological releases of CO2 occurred through mantle plume eruptions at ~260-250 Ma (Emeishan, Siberian Traps), ~210-190 Ma (Central Atlantic Magmatic Province), ~65 Ma (Deccan Traps), a ~130 Ma peak in subducting plate area (including carbonate sediments), as well as the magmatic decarbonation of carbonate platforms during Tethyan subduction at ~75-50 Ma. These events have been modulated by the near-equatorial weathering of LIPs particularly during ~260-160 and ~100-0 Ma, as well as the Alpine-Tethyan orogens and obducted ophiolites since the Late Cretaceous. Although we rely on present-day measurements to calibrate the deep-time tectonic components of the planetary carbon cycle, it becomes necessary to challenge uniformitarian assumptions. Our work highlights the need to quantify tectonic CO2 fluxes through time, but also better capture interactions with other physical and biological systems in order to study past climate change and implications for the biosphere.