The study, published in Communications Earth and Environment, reconstructs how carbon moved between the deep Earth, seafloor spreading centres, volcanic arcs and the oceans through the Phanerozoic eon. Led by researchers at the Universities of Melbourne and Sydney, the analysis links plate tectonic reconstructions with global carbon cycle models to trace how carbon was stored, released and recycled as continents assembled, broke apart and drifted.
Lead author Dr Ben Mather from the University of Melbournes School of Geography, Earth and Atmospheric Sciences said the findings challenge the long held view that volcanic arcs built above colliding tectonic plates are the primary natural source of atmospheric carbon dioxide over deep time. "Our findings show that carbon gas released from gaps and ridges deep under the ocean from moving tectonic plates was instead likely driving major shifts between icehouse and greenhouse climates for most of Earths history," Dr Mather said.
By focusing on the mid ocean ridges and related spreading systems, the team identified a strong connection between seafloor carbon outgassing and swings between cold and warm global states. The results indicate that when seafloor spreading accelerated or reorganised, enhanced carbon release from beneath the oceans could push the climate toward greenhouse conditions, whereas reduced spreading and carbon outflow favoured extended icehouse intervals.
"We found that carbon emitted from volcanoes, around the Pacific ring of fire for example, only became a major carbon source in the last 100 million years, which challenges current scientific understanding," Dr Mather said. Earlier in Earths history, diffuse degassing along the vast network of spreading centres appears to have overshadowed the contribution from volcanic arcs at convergent plate boundaries.
Co author Professor Dietmar Muller from the University of Sydneys School of Geosciences said pairing detailed plate motion reconstructions with carbon cycle modelling allowed the team to reconstruct how tectonics steered atmospheric carbon levels. By tracking when and where plates separated or collided, the researchers could estimate how much carbon was likely injected into the oceans and atmosphere, and how much was drawn back down into the mantle in subduction zones.
"Our studys findings help explain key historical climate shifts, including the late Paleozoic ice age, the warm Mesozoic greenhouse world, and the emergence of the modern Cenozoic icehouse, by showing how changes in carbon released from spreading plates shaped these long term transitions to our climate," Professor Muller said. The framework links tectonic reorganisations to well known climatic turning points, highlighting the central role of deep Earth processes in driving surface environment changes.
Dr Mather said the work provides important context for the rapid climate change currently underway. "This research adds to a large pool of evidence that the amount of carbon in the Earths atmosphere is a key trigger to cause major swings in climate," he said. He noted that while tectonic processes can profoundly alter climate, they operate over millions of years, in contrast to the much faster pulse of carbon now coming from human activities.
"Understanding how Earth controlled its climate in the past highlights how unusual the present rate of change is. Human activities are now releasing carbon far faster than any natural geological process that weve seen to have taken place before. The climate scales are being tipped at an alarming rate," Dr Mather said. The authors argue that recognising the slow but powerful influence of plate tectonics on climate underscores just how strongly modern emissions have disrupted the planets long standing carbon balance.
The study draws on recent advances in global plate kinematic models, which reconstruct the positions and motions of continents and ocean basins over the last 540 million years. By integrating these reconstructions with models of mantle melting, seafloor hydrothermal systems and sediment subduction, the team assembled a comprehensive picture of how carbon cycled between Earths interior and surface environments over geological time.
The researchers conclude that tectonic plate divergence at mid ocean ridges has been the dominant geological driver of atmospheric carbon dioxide and climate state for much of Earths history, with volcanic arcs rising to prominence only in the more recent past. They suggest that future work combining high resolution plate models with additional geochemical records could further refine the timing and magnitude of tectonically driven carbon fluxes, providing an even clearer view of how Earths interior and surface have co evolved.
Research Report:Tectonic controls on Phanerozoic plate carbon degassing and climate transitions
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