Béarn : des chercheurs tentent de percer les mystères d’une eau aux « caractéristiques uniques au monde »

Béarn : des chercheurs tentent de percer les mystères d’une eau aux « caractéristiques uniques au monde »

This CNRS researcher, who has worked in the geochemistry section for more than 20 years, took a Paris-Tarbes train on Thursday and then the car for an hour to reach the small chapel. The trip is worth it: from there springs a spring of sulphurous water with exceptional characteristics, which according to…

This CNRS researcher, who has worked in the geochemistry section for more than 20 years, took a Paris-Tarbes train on Thursday and then the car for an hour to reach the small chapel. The trip is worth it: sulphurous spring water of exceptional characteristics springs from there which, according to our researcher, presents “chemical anomalies unique in the world”.

Now converted into a spa house, the place itself has a unique history: it is the last active survivor of the small spa establishments that dotted the foothills of the Pyrenees centuries ago.

The chapel water presents chemical “anomalies” unique in the world

The origin of emergency baths dates back, according to legend, to Gallo-Roman times. Cut stones found near the springs show that the waters were already in use 2,500 years before Christ.

Later, in 1750, Théophile de Bordeu, a native of the Vallée d’Ossau, already speaks in his letters of a small establishment, quite rudimentary, but with miraculous springs where the inhabitants of the neighborhood went to treat all kinds of ailments. However, for quite some time, this water of unknown characteristics and particular smell gave the site the name of “witch” water. “Smells a bit like a rotten egg, what a stench! comments Peter.

The bath house was rebuilt in 1787 and then enlarged in 1866, but no one has managed to discover the secret of its waters.

unexplained abnormalities

At the entrance to the thermal house, you must take off your shoes and not make noise to respect the place of meditation and rest. Inside, people go to recharge their batteries in bathrooms with revitalizing properties.


To analyze this unique water, Pierre Cartigny goes once a month to the thermal house to patiently collect the water from the source itself.

Patrice Martins de Barros

At the foot of the thermal house, a chapel, about 10 mtwo welcomes the visitor, illuminated by a beautiful light filtered through a stained glass window. Above all, it houses the spring water that our researcher is so interested in. A small hole, about a foot on a side, contains the water that is poured into it. Who pours into it from where? “We don’t even know,” smiles Pierre Cartigny. “We know almost nothing about this source, it’s crazy. As the baths have existed for more than two centuries, there is no written record of their origin. »

The water has sulfur isotope anomalies. The source is “abnormal” because the hydrogen sulfide it contains (referred to as H2S, which smells like rotten eggs) is enriched in sulfur-33 and the sulfates (referred to as SO4) are depleted in sulfur-33.

The mechanism that produces these abnormalities is not understood. It could be microbial in origin (or not) and is even more concerning as all other sources in the region (which have been resampled and analyzed) show no anomalies.

Almost nothing is known about this source.

Pierre Cartigny remembers 2018, when Guillaume Barré, then a young researcher at Total, had to resample many sources to verify his values. He goes to this chapel in Béarn and notices a sulfur isotopic anomaly in this water. After Guillaume’s return to the laboratory, Pierre remembers his reaction: “I told him that he must have made a mistake in his samples, because these anomalies are extremely rare”, he smiles today. But subsequent samples tracked the same abnormalities, and researchers began to pay attention.

A reagent inside the bottles allows the isotopes to settle for analysis.


A reagent inside the bottles allows the isotopes to settle for analysis.

Patrice Martins de Barros

After the health crisis period, research is carried out at the CNRS. Every month, Pierre and his colleague from Pau, Anthony Ranchou-Peyruse, go to the chapel and fill several liters of this unique water. Once back in Paris, he will undergo many experiments: “First, we filter it to obtain only the reagent and the powder thus created. Several other transformations are carried out until we obtain a molecule that we know how to compare with other molecules and from which we can extract values. »

The sulfur isotope anomalies (in red) of this water, described here over several billion years.


The sulfur isotope anomalies (in red) of this water, described here over several billion years.

pierre cartigny

The anomalies of the water here schematized.


The anomalies of the water here schematized.

pierre cartigny

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