Scientists at the University of Southampton have discovered that extensive chains of volcanoes have been responsible for both emitting and then removing atmospheric carbon dioxide (CO2) over geological time. This may have stabilized temperatures at the Earth’s surface over hundreds of thousands of years.
The researchers, working with colleagues at the University of Sydney, Australian National University (ANU), University of Ottawa and University of Leeds, explored the combined impact of processes in the solid Earth, oceans and atmosphere over the past 400 million years. Their findings are published in the journal Nature Geoscience.
Natural break-down and dissolution of rocks at Earth’s surface is called chemical weathering. It is critically important because the products of weathering (elements like calcium and magnesium) are flushed via rivers to the oceans, where they form minerals that lock up CO2. This feedback mechanism regulates atmospheric CO2 levels, and in turn global climate, over geological time.
To unravel the complexity, the team constructed a novel “Earth network”, incorporating machine-learning algorithms and plate tectonic reconstructions. This enabled them to identify the dominant interactions within the Earth system, and how they evolved through 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 comprise chains of volcanoes in, for example, the Andes in South America, and the Cascades in the US. These volcanoes are some of the highest and fastest eroding features on Earth. Because the volcanic rocks are fragmented and chemically reactive, they are rapidly weathered and flushed into the oceans.
The study casts doubt on a long-held concept that Earth’s climate stability over tens to hundreds of millions of years reflects a balance between weathering of the seafloor and continental interiors.
But the team’s findings still provide critical insights into how society might manage the current climate crisis. Artificially enhanced rock weathering - where rocks are pulverised and spread across land to speed up chemical reaction rates - could play a key role in safely removing CO2 from the atmosphere. The team’s findings suggest that such schemes may be deployed optimally by using calc-alkaline volcanic materials (those containing calcium, potassium and sodium), like those found in continental arc environments.