Evolution of Earth’s tectonic carbon conveyor belt

May 26, 2022·

Dietmar Muller

Ben Mather

Adriana Dutkiewicz

Tobias Keller

Andrew Merdith

Chris Gonzalez

Weronika Gorczyk

Sabin Zahirovic

· 2 min read

DOI

The Earth’s tectonic carbon conveyor belt shifts massive amounts of carbon between the deep Earth and the surface, from mid-ocean ridges to subduction zones, where oceanic plates carrying deep-sea sediments are recycled back into the Earth’s interior. The processes involved play a pivotal role in Earth’s climate and habitability.

Abstract

Concealed deep beneath the oceans is a carbon conveyor belt, propelled by plate tectonics. Our understanding of its modern functioning is underpinned by direct observations, but its variability through time has been poorly quantified. Here we reconstruct oceanic plate carbon reservoirs and track the fate of subducted carbon using thermodynamic modelling. In the Mesozoic era, 250 to 66 million years ago, plate tectonic processes had a pivotal role in driving climate change. Triassic–Jurassic period cooling correlates with a reduction in solid Earth outgassing, whereas Cretaceous period greenhouse conditions can be linked to a doubling in outgassing, driven by high-speed plate tectonics. The associated ‘carbon subduction superflux’ into the subcontinental mantle may have sparked North American diamond formation. In the Cenozoic era, continental collisions slowed seafloor spreading, reducing tectonically driven outgassing, while deep-sea carbonate sediments emerged as the Earth’s largest carbon sink. Subduction and devolatilization of this reservoir beneath volcanic arcs led to a Cenozoic increase in carbon outgassing, surpassing mid-ocean ridges as the dominant source of carbon emissions 20 million years ago. An increase in solid Earth carbon emissions during Cenozoic cooling requires an increase in continental silicate weathering flux to draw down atmospheric carbon dioxide, challenging previous views and providing boundary conditions for future carbon cycle models.

Type

Journal article

Publication

Nature

Plain Language Summary

Hidden beneath the world’s oceans is a giant carbon conveyor belt, driven by the movement of tectonic plates. As new ocean floor forms at mid-ocean ridges, it absorbs carbon from seawater into its rocks and sediments. When this ocean floor is eventually pulled back into the Earth’s interior at subduction zones, some of that carbon is released back into the atmosphere through volcanic eruptions, while the rest is carried deeper into the mantle.

This study reconstructs how this tectonic carbon conveyor belt has operated over the past 250 million years. During the Cretaceous period, high-speed plate tectonics doubled volcanic CO₂ emissions, contributing to one of Earth’s warmest climates. The massive amount of carbon subducted during this time may even have triggered diamond formation beneath North America. As continental collisions later slowed seafloor spreading in the Cenozoic era, tectonic outgassing declined — but a new twist emerged: deep-sea carbonate sediments became the Earth’s largest carbon sink, and their recycling through subduction beneath volcanic arcs made arcs the dominant source of CO₂ emissions from about 20 million years ago.

The finding that solid Earth carbon emissions actually increased during the Cenozoic cooling period challenges previous assumptions and implies that continental weathering must have ramped up even more dramatically to draw down atmospheric CO₂ and cool the planet.

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