Scientists from the University of Southampton have found that vast chains of volcanoes are responsible for both the emission and removal of atmospheric carbon dioxide (CO2) over geologic time. This stabilized temperatures on the Earth’s surface.
The researchers, in collaboration with colleagues from the University of Sydney, Australian National University (ANU), the University of Ottawa and the University of Leeds, explored the combined impact of processes on the solid Earth, oceans and atmosphere over the past 400 million years. Their findings are published in the journal Nature Geoscience is a monthly peer-reviewed scientific journal published by the Nature Publishing Group that covers all aspects of the Earth sciences, including theoretical research, modeling, and fieldwork. Other related work is also published in fields that include atmospheric sciences, geology, geophysics, climatology, oceanography, paleontology, and space science. It was established in January 2008.
The natural breakdown and dissolution of rocks on the Earth’s surface is called chemical weathering. It is extremely important because weathering products (elements like calcium and magnesium) are flushed by rivers to the oceans, where they form minerals that trap CO2. This feedback mechanism regulates atmospheric CO2 levels, and in turn the global climate, over geologic time.
“In this respect, the weathering of the Earth’s surface serves as a geological thermostat,” says lead author Dr Tom Gernon, Associate Professor of Earth Sciences at the University of Southampton and Fellow of the Institute. Turing. “But the underlying controls have proven difficult to determine due to the complexity of the Earth system.”
“Many terrestrial processes are linked and there are significant time lags between the processes and their effects,” says Eelco Rohling, professor of ocean and climate change at ANU and co-author of the study. “Understanding the relative influence of specific processes in the Earth system response has therefore been an intractable problem.”
To unravel the complexity, the team built a new ‘earth network’, incorporating machine learning algorithms and plate tectonic reconstructions. This allowed them to identify the dominant interactions within the Earth system and their evolution over time.
The team found that continental volcanic arcs were the most important driver of weathering intensity over the past 400 million years. Today, continental arcs include chains of volcanoes, for example in the Andes in South America and the Cascades in the United States. These volcanoes are among the highest and fastest eroding features on Earth. Because volcanic rocks are fragmented and chemically reactive, they are quickly weathered and released into the oceans.
Martin Palmer, professor of geochemistry at the University of Southampton and co-author of the study, said: “It’s a balancing act. On the one hand, these volcanoes pumped large amounts of CO2 which increased atmospheric CO2 levels. On the other hand, these same volcanoes helped remove this carbon via rapid weathering reactions.
The study casts doubt on a long-held concept that Earth’s climatic stability over tens to hundreds of millions of years reflects a balance between seabed weathering and the interiors of continents. “The idea of such a geological standoff between landmasses and the seabed as the dominant driver of weathering of the Earth’s surface is not supported by the data,” says Dr Gernon.
“Unfortunately, the results do not mean that nature will save us from climate change,” says Dr Gernon. “Today, atmospheric CO2 levels are higher than at any time in the past 3 million years, and human-caused emissions are about 150 times greater than volcanic CO2 emissions. The continental arcs that seem to have saved the planet in the distant past are simply not present on the scale needed to help counter today’s CO.2 emissions.
But the team’s findings still provide critical insights into how society could handle the current climate crisis. Artificially enhanced rock weathering – where rocks are pulverized and spread over the ground to speed up chemical reaction rates – could play a key role in safely removing CO2 of the atmosphere. The team’s findings suggest that such schemes can be best deployed using calc-alkaline volcanic materials (those containing calcium, potassium and sodium), such as those found in the environments of continental arc.
“This is by no means a silver bullet to the climate crisis – we urgently need to reduce CO2 emissions in line with IPCC mitigation pathways, full stop. Our assessment of weathering feedbacks over long time periods can help design and evaluate large-scale weathering programs, which are just one of the steps needed to counter global climate change,” concludes Dr. Gernon.
Reference: “Global chemical weathering dominated by continental arcs since the middle of the Paleozoic” by Thomas M. Gernon, Thea K. Hincks, Andrew S. Merdith, Eelco J. Rohling, Martin R. Palmer, Gavin L. Foster, Clément P Bataille and R. Dietmar Müller, August 23, 2021, Nature Geoscience.