Humanitarian Media Hub provides a translation of a study written by researchers for The Conversation.Authors of the study:
- Ben Meiser — ARC Early Career Research Fellow, School of Geography, Earth and Atmospheric Sciences, University of Melbourne.
- Adriana Dutkevych — ARC Future Fellow, specialising in sedimentology, University of Sydney.
- Dietmar Müller — Professor of Geophysics, University of Sydney.
- Sabine Zahirovich — ARC DECRA Fellow, School of Geosciences, University of Sydney.
Throughout Earth’s geological history, the climate has changed repeatedly — from icy “glacial periods” to warm “greenhouse” epochs. These fluctuations are closely related to the level of carbon dioxide in the atmosphere. But where does this carbon come from and what exactly triggers its release — these questions are more complex than previously thought.
New research shows that the main drivers of climate change may be not only volcanoes, but also the divergence of tectonic plates, in particular mid-ocean ridges and continental rifts. This discovery reinterprets the role of geological processes in the planet’s carbon cycle.
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Deep carbon cycle
Where tectonic plates converge, volcanic arcs form. When these arcs form, carbon that has been trapped in rocks for millennia is released from the Earth’s interior. Previously, these arcs were considered the main source of atmospheric CO₂.
However, new research published in the journal Communications Earth & Environment shows that places where plates diverge — in particular, mid-ocean ridges and continental rifts — also play a significant role. It is there that carbon accumulated in the sedimentary rocks of the seabed is released.
Oceans are capable of absorbing huge amounts of CO₂. Over time, this carbon settles in limestone rocks at the bottom, forming thick layers of carbon deposits. When these rocks, moving with the plates, enter subduction zones — places where one plate dives under another — the carbon returns to the atmosphere.
Climate modelling over 540 million years
Using computer modelling, scientists traced how plate movement affected the climate. It turned out that during warm greenhouse periods, carbon was released faster than it accumulated in rocks. During cold ice ages, CO₂ absorption prevailed, contributing to global cooling.
Seafloor sediments proved to be a key element. They provide a balance between carbon emissions and absorption, and their subsequent fate — subduction or accumulation — determines the planet’s climate.
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Revisiting the role of volcanic arcs
For a long time, volcanic arcs were considered the main source of carbon dioxide. But this situation has only existed for the last 120 million years — after the appearance of plankton, which forms carbon-containing calcite. They convert carbon dissolved in water into solid sediments, which later become a source of CO₂ for volcanoes.
Before the appearance of these organisms, the main sources of atmospheric carbon were mid-ocean ridges and faults. They determined the carbon balance in the atmosphere for most of Earth’s history.
Climate influenced by geology
The results obtained change our understanding of the role of tectonics in climate change. Atmospheric carbon is only part of the story. Equally important are the deep geological processes that govern the circulation of carbon between the Earth’s interior, the ocean and the atmosphere.
Understanding these processes allows for a deeper assessment of long-term climate change. It also opens up new opportunities for more accurate predictions of the future, taking into account that current warming is unfolding against the backdrop of a natural, million-year carbon cycle.
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