Deserts may seem lifeless and inert, but they are very much alive. Sand dunes, in particular, grow and move — and according to a decades long research project, they also breathe humid air.
The findings show for the first time how water vapor penetrates powders and grains, and could have wide-ranging applications far beyond the desert — in pharmaceutical research, agriculture and food processing, as well as planetary exploration.
The team’s paper published in the Journal of Geophysical Research-Earth Surface.
Wanting to measure matter with greater sensitivity, lead author Michel Louge, professor of mechanical and aerospace engineering at Cornell University, developed a new form of instrumentation called capacitance probes, which use multiple sensors to record everything from solid concentration to velocity to water content, all with unprecedented spatial resolution.
In the early 2000s, Louge began collaborating with Ahmed Ould el-Moctar from University of Nantes, France, to use the probes to study the moisture content in sand dunes to better understand the process by which agricultural lands turn to desert — an interest that has only become more urgent with the rise of global climate change.
The probe eventually revealed just how porous sand is, with a tiny amount of air seeping through it. Previous research hinted this type of seepage existed in sand dunes, but no one had been able to prove it until now.
“The wind flows over the dune and as a result creates imbalances in the local pressure, which literally forces air to go into the sand and out of the sand. So, the sand is breathing, like an organism breathes,” Louge said.
That “breathing” is what allows microbes to persist deep inside hyper-arid sand dunes, despite the high temperature. For much of the last decade, Louge has been collaborating with Anthony Hay, associate professor of microbiology at Cornell, to study how microbes can help stabilize the dunes and prevent them from encroaching into roads and infrastructure.
Louge and his team also determined that desert surfaces exchange less moisture with the atmosphere than expected, and that water evaporation from individual sand grains behaves like a slow chemical reaction.
The bulk of their data was gathered in 2011, but it still took Louge and his collaborators another decade to make sense of some of the findings, such as identifying disturbances at the surface level that force evanescent, or nonlinear, waves of humidity to propagate downward through the dunes very quickly.
The researchers anticipate their probe will have a number of applications — from studying the way soils imbibe or drain water in agriculture, to calibrating satellite observations over deserts, to exploring extraterrestrial environments that may hold trace amounts of water. That wouldn’t be the first time Louge’s research made its way into space.
But perhaps the most immediate application is the detection of moisture contamination in pharmaceuticals. Since 2018, Louge has been collaborating with Merck to use the probes in continuous manufacturing, which is viewed as a faster, more efficient and less expensive system than batch manufacturing.