New study reveals Earth’s crust has largest reservoir of water, ahead of ice sheets
New modelling by Earth 4D researchers quantifies salty water reservoirs found two to 10 kilometres underground, doubling previous estimates
CIFAR’s Earth 4D fellows are among a team of researchers to detect a significant water reservoir under the Earth’s crust. The volume they’ve calculated is larger than the amount of water in ice sheets.
“We quickly realized that by working together we could take a fresh approach on an important question – just how much groundwater does the planet hold?” says Barbara Sherwood Lollar, on the collaboration with Earth 4D members.
Using Crust 1.0, a global database of all rocks making up the uppermost layers of the Earth’s crust, the researchers estimated nearly 44 million cubic kilometres of water is found two to 10 kilometres underground. In comparison, the amount of water held in ice sheets in Antarctica is estimated at 27 million cubic kilometres.
Previous estimates of groundwater also quantified just portions of the Earth’s crust in the upper two kilometres. Three years ago, Oliver Warr, a research associate in Sherwood Lollar’s lab, and Earth 4D members hypothesized that saline groundwater much deeper in the crust was a largely under-investigated reservoir.
“What this new paper does is confirm the vast amount of deep groundwater previously estimated, but also to advance the discipline by including not only crystalline rocks but sedimentary rocks,” says Sherwood Lollar, co-author of the paper, co-director of CIFAR’s Earth 4D: Subsurface Science & Exploration program, and professor at the University of Toronto.
Their findings were recently published in Geophysical Research Letters.
“By focusing on what exists at the two-to-10 kilometres depth — it has doubled pre-existing estimates for groundwater on a global scale,” adds Sherwood Lollar.
Jennifer McIntosh, a fellow of the Earth E4D program, says the team’s findings will also help advance researchers’ understanding of deep groundwater systems and what challenges it could address above the surface.
“Deep groundwater systems are still a scientific frontier – we know little about the distribution, quality, and age of water beyond two kilometres, because our windows into the subsurface, such as deep wells, boreholes, mines, are few and far between,” explains McIntosh, a professor at the University of Arizona. “Yet, we know from the few locations that have been explored, these deep groundwater systems support microbial life and contain elements and gases that are important for our growing carbon-neutral economy.”
The study was supported by the CIFAR Catalyst Fund and led by Grant Ferguson, professor at the University of Saskatchewan, alongside E4D program members Sherwood Lollar, McIntosh, John Mustard (program co-director), Jeff McDonnell (advisor), Chris Ballentine (Fellow), Joseph Michalski (Fellow), alongside Warr, postdoctoral fellow Jesse Tarnas and PhD student Ji-Hyun Kim.
Sherwood Lollar said this discovery and the catalyst for the paper would not have been possible if not for the ideas discussed in CIFAR Earth 4D program meetings.
“CIFAR’s support and catalytic funding strategies are essential to work such as this,” she says. “Where big questions relevant to science and society were brainstormed by a new team, drawing from international talent representing diverse disciplines, from geology, to microbiology, to physics and planetary sciences.”
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