Duke study: serpentinized rock in oceans may be large, overlooked source of free hydrogen gas
21 July 2016
Rocks formed beneath the ocean floor by fast-spreading tectonic plates may be a large and previously overlooked source of free hydrogen gas, a new Duke University study suggests. Their paper is published in the journal Geophysical Research Letters.
Recent discoveries of free hydrogen gas, which was once thought to be very rare, have been made near slow-spreading tectonic plates deep beneath Earth’s continents and under the sea. Previous estimates suggest that serpentinization—a processes whereby rock is changed, with the addition of water, into the crystal structure of the minerals found within the rock—within the continental lithosphere (the crust and upper mantle of the earth) produces hydrogen at rates comparable to the oceanic lithosphere (both are ~1011 mol H2/yr).
| Serpentinized rocks are so called because they often have a scaly, greenish-brown-patterned surface that resembles snakeskin. |
The Duke researchers presented a simple model that suggests that H2 production rates along the mid-oceanic ridge alone (i.e., excluding other marine settings) may exceed continental production by an order of magnitude (~1012 mol H2/yr).
In the Duke model, hydrogen production rates increase with spreading rate and the net thickness of serpentinizing peridotite (S-P) in a column of lithosphere. Lithosphere with a faster spreading rate therefore requires a relatively smaller net thickness of S-P to produce H2 at the same rate as lithosphere with a slower rate and greater thickness of S-P.
A major benefit of this work is that it provides a testable, tectonic-based model for not only identifying where free hydrogen gas may be forming beneath the seafloor, but also at what rate, and what the total scale of this formation may be, which on a global basis is massive.
—co-author Lincoln F. Pratson, professor of earth and ocean sciences at Duke
The new model calculates the amount of free hydrogen gas produced and stored beneath the seafloor based on a range of parameters—including the ratio of a site’s tectonic spreading rate to the thickness of serpentinized rocks that might be found there.
Most scientists previously thought all hydrogen production occurs only at slow-spreading lithosphere, because this is where most serpentinized rocks are found. Although faster-spreading lithosphere contains smaller quantities of this rock, our analysis suggests the amount of H2 produced there might still be large.
Right now, the only way to get H2—to use in fuel cells, for example—is through secondary processes. You start with water, add energy to split the oxygen and hydrogen molecules apart, and get H2. You can then burn the H2, but you had to use energy to get energy, so it’s not very efficient.
—Stacey L. Worman, postdoc at UT Austin, who led the study while a doctoral student at Duke
Mining free hydrogen gas as a primary fuel source could change that, but first scientists need to understand where the gas goes after it’s produced.
Maybe microbes are eating it, or maybe it’s accumulating in reservoirs under the seafloor. We still don’t know. Of course, such accumulations would have to be quite significant to make hydrogen gas produced by serpentinization a viable fuel source.
—Stacey Worman
If further research confirms the model’s accuracy, it could also open new avenues for exploring the origin of life on Earth, and for understanding the role hydrogen gas might play in supporting life in a wide range of extreme environments, from the sunless deep-sea floor to distant planets.
Worman and Pratson conducted the study with Jeffrey Karson, professor of earth sciences at Syracuse University, and Emily Klein, professor of earth sciences at Duke.
Resources
Stacey L. Worman, Lincoln F. Pratson, Jeffrey Karson, Emily Klein (2016) “Global Rate and Distribution of H2 Gas Produced by Serpentinization within Oceanic Lithosphere” Geophysical Research Letters doi: 10.1002/2016GL069066
It should only take 20 years or so for battery only people to catch up, and modify the 'hydrogen is an energy carrier, not a resource' meme.
Mind you, they still use the same duff math as they always have to falsely claim that battery electric cars are many times as energy efficient as fuel cell ones, by the simple expedient of ignoring all electricity generation and transmission losses and assuming the cars are all charged on the sun which never sets in their world.
Posted by: Davemart | 21 July 2016 at 03:12 AM
And it might take the fuel cell people 20 years before they even know if this "free hydrogen" can be mined. And if it can be - at what price? And at what cost to the biosphere if this food source deep sea microbes is tamper with? Or how long the reservoirs, if they exist, will last once we start tapping them.
"Mining free hydrogen gas as a primary fuel source could change that, but first scientists need to understand where the gas goes after it’s produced.
Maybe microbes are eating it, or maybe it’s accumulating in reservoirs under the seafloor. We still don’t know. Of course, such accumulations would have to be quite significant to make hydrogen gas produced by serpentinization a viable fuel source."
Posted by: ai_vin | 21 July 2016 at 08:04 AM
10^11 moles = 2*10^8 kg = 2*10^5 tons.
Nothing to see here, move along.
Posted by: Engineer-Poet | 21 July 2016 at 01:29 PM
10^12 moles, so 2*10^6 tons, or about 1/5th of current H2 production level.
Posted by: matt | 21 July 2016 at 03:24 PM
Well 1/5th of current H2 production level isn't bad really, but even if this gas does pool into reservoirs it's still at the bottom of the ocean. A expensive place to drill. More likely, given the nature of H2, it just diffuses into the surrounding rock where it either gets eaten by microdes or reacts with other elements to form compounds like CH4. Do we need another source of natural gas?
Posted by: ai_vin | 21 July 2016 at 09:02 PM