Human impact on Earth's deep subsurface fluid dynamics revealed

Recent studies by University of Arizona hydrologists have provided insights into the effects of human activities on the deep subsurface of Earth. The research focuses on areas that are hundreds of meters to several kilometers below the surface, which have not been as extensively studied as Earth's surface.

"We looked at how the rates of fluid production with oil and gas compare to natural background circulation of water and showed how humans have made a big impact on the circulation of fluids in the subsurface," said Jennifer McIntosh, a professor at UArizona and senior author of the study published in Earth's Future.

"The deep subsurface is out of sight and out of mind for most people, and we thought it was important to provide some context to these proposed activities, especially when it comes to our environmental impacts," said Grant Ferguson, lead study author and an adjunct professor at UArizona.

The study predicts an increase in human-induced fluid fluxes with future strategies aimed at addressing climate change. These include geologic carbon sequestration, geothermal energy production, and lithium extraction, conducted in collaboration with several international universities and institutes.

"Responsible management of the subsurface is central to any hope for a green transition, sustainable future and keeping warming below a few degrees," said Peter Reiners, a co-author and professor at UArizona.

McIntosh explained that in processes like oil and natural gas production, saline water, often millions of years old, is produced from the deep subsurface. To aid oil recovery, this saline water is blended with near-surface water and reinjected, establishing a cycle of fluid production and reinjection.

"This becomes a cycle of producing fluid and reinjecting it to the deep subsurface. The same process happens in lithium extraction, geothermal energy production, and geologic carbon sequestration," McIntosh noted.

The team utilized various data sources to establish that current rates of fluid movement due to human activities surpass natural rates. As activities like carbon capture and lithium extraction expand, their geological impacts are also anticipated to be significant.

"The potential alterations to deep subsurface microbes are also significant, as movements change water chemistry and introduce surface microbes to underground environments," McIntosh added.

In conclusion, the team emphasized the ongoing need to explore the deep subsurface to fully understand its role in addressing the climate crisis, drawing an interesting comparison: "We need to use the deep subsurface as part of the solution for the climate crisis," McIntosh said. "Yet, we know more about the surface of Mars than we do about water, rocks, and life deep beneath our feet."