Simulations reveal how saltwater behaves in Earth's mantle

June 24, 2020

Scientists estimate that the Earth's mantle holds as much water as all the oceans on the planet, but understanding how this water behaves is difficult. Water in the mantle exists under high pressure and at elevated temperatures, extreme conditions that are challenging to recreate in the laboratory.

That means many of its physical and chemical properties--relevant to understanding magma production and the Earth's carbon cycle -- aren't fully understood. If scientists could better understand these conditions, it would help them better understand the carbon cycle's consequences for climate change.

A team led by Prof. Giulia Galli and Prof. Juan de Pablo from the Pritzker School of Molecular Engineering (PME) at the University of Chicago and Prof. Francois Gygi from the University of California, Davis has created complex computer simulations to better understand the properties of salt in water under mantle conditions.

By coupling simulation techniques developed by the three research groups and using sophisticated codes, the team has created a model of saltwater based on quantum mechanical calculations. Using the model, the researchers discovered key molecular changes relative to ambient conditions that could have implications in understanding the interesting chemistry that lies deep beneath the Earth's surface.

"Our simulations represent the first study of the free energy of salts in water under pressure," Galli said. "That lays the foundation to understand the influence of salt present in water at high pressure and temperature, such as the conditions of the Earth's mantle." The results were published June 16 in the journal Nature Communications.

Important in fluid-rock interactions

Understanding the behavior of water in the mantle is challenging -- not only because it is difficult to measure its properties experimentally, but because the chemistry of water and saltwater differs at such extreme temperatures and pressures (which include temperatures of up to 1000K and pressures of up to 11 GPa, 100,000 times greater than on the Earth's surface.)

While Galli previously published research on the behavior of water in such conditions, she and her collaborators at the Midwest Integrated Center for Computational Materials (MICCoM) have now extended their simulations to salt in water, managing to predict much more complex properties than previously studied.

The simulations, performed at UChicago's Research Computing Center using optimized codes supported by MICCoM, showed key changes of ion-water and ion-ion interactions at extreme conditions. These ion interactions affect the free energy surface of salt in water.

Specifically, researchers found that dissociation of water that happens due to high pressure and temperature influences how the salt interacts with water and in turn how it is expected to interact with surfaces of rocks at the Earth's surface.

"This is foundational to understanding chemical reactions at the conditions of the Earth's mantle," de Pablo said.

"Next we hope to use the same simulation techniques for a variety of solutions, conditions, and other salts," Gygi said.
-end-
Other authors on the paper include Cunzhi Zhang of Peking University; UChicago postdoctoral research fellow Federico Giberti; and UChicago graduate student Emre Sevgen.

Citation: "Dissociation of salts in water under pressure." Zhang et al, Nature Communications. DOI: 10.1038/s41467-020-16704-9

Funding: Department of Energy

University of Chicago

Related Carbon Cycle Articles from Brightsurf:

Who is driving whom? Climate and carbon cycle in perpetual interaction
The current climate crisis underlines that carbon cycle perturbations can cause significant climate change.

Metal wires of carbon complete toolbox for carbon-based computers
Carbon-based computers have the potential to be a lot faster and much more energy efficient than silicon-based computers, but 2D graphene and carbon nanotubes have proved challenging to turn into the elements needed to construct transistor circuits.

Uncovering new understanding of Earth's carbon cycle
A new study led by a University of Alberta PhD student--and published in Nature--is examining the Earth's carbon cycle in new depth, using diamonds as breadcrumbs of insight into some of Earth's deepest geologic mechanisms.

Understanding the 'deep-carbon cycle'
New geologic findings about the makeup of the Earth's mantle are helping scientists better understand long-term climate stability andĀ even how seismic waves move through the planet's layers.

Artificial intelligence helps researchers up-cycle waste carbon
Researchers at University of Toronto Engineering and Carnegie Mellon University are using artificial intelligence (AI) to accelerate progress in transforming waste carbon into a commercially valuable product with record efficiency.

Closing the carbon cycle to stop climate change
Reducing the CO2 levels in the Earth's atmosphere is key to stopping environmental degradation.

FSU researchers find newly uncovered Arctic landscape plays important role in carbon cycle
As the ice sheet covering most of Greenland retreats, Florida State University researchers are studying the newly revealed landscape to understand its role in the carbon cycle.

Scientists show solar system processes control the carbon cycle throughout Earth's history
This new work sheds fresh light on the complicated interplay of factors affecting global climate and the carbon cycle -- and on what transpired millions of years ago to spark two of the most devastating extinction events in Earth's history.

Can wood construction transform cities from carbon source to carbon vault?
A new study by researchers and architects at Yale and the Potsdam Institute for Climate Impact Research predicts that a transition to timber-based wood products in the construction of new housing, buildings, and infrastructure would not only offset enormous amounts of carbon emissions related to concrete and steel production -- it could turn the world's cities into a vast carbon sink.

Increasing tropical land use is disrupting the carbon cycle
An international study led by researchers at Lund University in Sweden shows that the rapid increase in land use in the world's tropical areas is affecting the global carbon cycle more than was previously known.

Read More: Carbon Cycle News and Carbon Cycle Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.