Volcanoes acted as a safety valve for Earth's long-term climate

Date:
August 23, 2021
Source:
University of Southampton
Summary:
Scientists have discovered that extensive chains of volcanoes have
been responsible for both emitting and then removing atmospheric
carbon dioxide over geological time. This stabilized temperatures
at Earth's surface.



FULL STORY ========================================================================== 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
stabilised temperatures at Earth's surface.


==========================================================================
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.

"In this respect, weathering of the Earth's surface serves as a geological thermostat," says lead author Dr Tom Gernon, Associate Professor in
Earth Science at the University of Southampton, and a Fellow of the
Turing Institute.

"But the underlying controls have proven difficult to determine due to the complexity of the Earth system." "Many Earth processes are interlinked,
and there are some major time lags between processes and their effects," explains Eelco Rohling, Professor in Ocean and Climate Change at ANU
and co-author of the study. "Understanding the relative influence of
specific processes within the Earth system response has therefore been an intractable problem." 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.

Martin Palmer, Professor of Geochemistry at the University of Southampton
and co-author of the study, said: "It's a balancing act. On one hand,
these volcanoes pumped out large amounts of CO2 that increased atmospheric
CO2 levels. On the other hand, these same volcanoes helped remove that
carbon via rapid weathering reactions." 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. "The idea of such a geological tug of war
between the landmasses and the seafloor as a dominant driver of Earth
surface weathering is not supported by the data," Dr Gernon states.

"Unfortunately, the results do not mean that nature will save us from
climate change," stresses Dr Gernon. "Today, atmospheric CO2 levels are
higher than at any time in the past 3 million years, and human-driven
emissions are about 150 times larger than volcanic CO2 emissions. The continental arcs that appear to have saved the planet in the deep past
are simply not present at the scale needed to help counteract present-day
CO2 emissions." 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.

"This is by no means a silver bullet solution 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 timescales may help in designing and evaluating large-scale enhanced
weathering schemes, which is just one of the steps needed to counteract
global climate change," Dr Gernon concludes.

========================================================================== Story Source: Materials provided by University_of_Southampton. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Thomas M. Gernon, Thea K. Hincks, Andrew S. Merdith, Eelco
J. Rohling,
Martin R. Palmer, Gavin L. Foster, Cle'ment P. Bataille, R. Dietmar
Mu"ller. Global chemical weathering dominated by continental
arcs since the mid-Palaeozoic. Nature Geoscience, 2021; DOI:
10.1038/s41561-021- 00806-0 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210823125827.htm

--- up 15 weeks, 3 days, 22 hours, 45 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1:317/3)