A decade-long research project to analyse the desert in the Gulf reached what might seem like a surprising conclusion: sand dunes can breathe.
The work showed how sand dunes exchange air with the environment around them and demonstrated that this can help the growth of microorganisms inside the dune.
By highlighting how sand dunes exchange water vapour — a greenhouse gas — with the surrounding air, the findings may improve the scientific understanding of desertification at a time of climate change.
Led by Prof Michel Louge, of Cornell University in the US, the researchers developed an ultra-sensitive probe that could detect the temperature and moisture on the surface of sand grains.
“Because the probe is so precise, it could measure how the moisture changes with time and space,” Prof Louge said.
“We could measure, for the first time, the flux of the moisture going in and out of the sand dune.”
While collecting data in Qatar, they found that when the wind blew over the surface of a dune and it skimmed off the upper layer, creating imbalances in the air pressure that resulted in weak air currents and “evanescent”, or fleeting, waves of moisture passing down through the dune.
“An analysis of these waves implies that water evaporation from individual sand grains behaves like a slow chemical reaction,” the researchers wrote in the Journal of Geophysical Research — Earth Surface.
Until the latest study, the way that sand dunes “inhaled” and “exhaled” water vapour was poorly understood because instruments lacked precision.
It had been thought that the exchange of moisture between the dune and the atmosphere was caused by a difference in humidity between the dune’s surface and the ambient air, but the latest research shows this is not always the case.
The movement of water vapour into the sand dune allows microorganisms to survive deep inside the structure of the dune, even when there may not be much liquid water inside.
The fieldwork was carried out at sand dunes near Mesaieed, south of Doha, and often involved overnight stays in the desert so that instruments could be checked to ensure they were running properly, as dozens of measurements were taken each hour.
In addition to recording measurements on and inside the dune, the researchers took air humidity and temperature readings, checked solar radiation, and monitored wind direction and speed.
They also worked at laboratories at Weill Cornell Medicine — Qatar, a branch of Cornell University near the Qatari capital.
The research took a decade to come to fruition because Prof Louge and his colleagues preferred to develop a definitive understanding of how dunes exchange moisture, rather than publish incremental studies that each revealed a small part of the picture.
Water vapour is a major greenhouse gas, so understanding how it moves into and out of dunes could help to create a better picture of how desertification may affect climate change.
“We found that much less water was exchanged across the surface than we anticipated. If you take that and multiply that by the surface of the large sand seas like the Sahara, it makes a big difference,” he said.
“It’s crucially important to understand what the deserts exhale and inhale. They’re found in a very large portion of the land mass, an increasing proportion.”
The findings could also improve scientists’ understanding of desertification, which is a growing threat as a result of climate change and habitat degradation.
Prof Louge hopes that Gulf states will invest more in studying sand dunes, because having laboratories close to the dunes makes research much easier.
Nations in the Gulf region are well placed to advance the field, he said.
“The governments of the Gulf states are very forward looking. They know all the ramifications of global climate change, the importance of sustainability, the changes and risks of desertification,” he said.
“They could put together institutions that bring together the best scientists … They have the intellect. They have all the resources needed … There’s so much that can be learnt.”
The other authors of the paper are Prof Alexandre Valance, of the Institute of Physics of Rennes, France, Dr Jin Xu, of Cornell University, Prof Ahmed Ould El Moctar, of the University of Nantes, France, and Patrick Chasle, of the Institute of Physics of Rennes.
Prof Louge’s research is the latest to unearth the hidden life of sand dunes, with a 2020 study from the University of Cambridge indicating that turbulence in the air or water created by one dune influenced neighbouring dunes.
As a result, dunes have been described as communicating with or repelling each other.
As reported in The National, the researchers found that water flowing through a circular chamber caused the dune further downstream, namely further from the incoming flow, to initially move faster.
However, at a certain distance apart, the two dunes’ speeds become the same and the downstream dune is no longer being “repelled” by the upstream one.
