June 5, 2023

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A remote laboratory is taking shape 2.5 kilometers below sea level – Ars Technica

Zoom in / Deployment of the LSPM junction box 1.


In 1962, one of the world’s first underwater and human habitat research laboratories was established off the coast of Marseille, France, at a depth of 10 metres. Project Conshelf 1 consisted of a steel structure that housed two men for a week.

Now, more than 60 years later, another underwater laboratory is being set up not far from Marseille, this time to study the sea and sky. Unlike the Conshelf forte, the Souss-Marine Provence Mediterranean Laboratory (LSPM) will not be inhabited by humans. Located 40 kilometers off the coast of Toulon at a depth of 2,450 metres, it is Europe’s first remotely operated underwater laboratory.

Undersea Physics

Currently, three junction boxes capable of running multiple tools and retrieving data are at the heart of LSPM. The boxes, each 6 meters long and 2 meters high, are connected to a power system on Earth via a 42-kilometre photovoltaic cable. The optical part of this cable is used to collect data from junction boxes.

Two of the junction boxes are assigned to the ORCA division of the Kilometer Cube Neutrino Telescope (KM3NeT). ORCA includes a three-dimensional array of 2,070 spheres, each containing 31 detectors called photomultiplier tubes. These spheres will be arranged on 115 lines that are anchored to the ocean floor and anchored by submerged buoys. Currently, 15 fonts have been installed.

Optical detection unit of the KM3NeT neutrino detector.

Optical detection unit of the KM3NeT neutrino detector.

Patrick Dumas/CNRS

ORCA’s twin site, ARCA, is located off the coast of Sicily at a depth of 3,400 metres. Collectively, the ORCA and ARCA sites occupy more than 1 cubic kilometer of water.

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“These giant arrays of detectors can detect neutrinos emitted from the southern hemisphere skies. On the rare occasions [the neutrinos] They interact with water molecules, producing a bluish flash of light in the darkness of the ocean abyss,” said Paschal Coel, director of research at the Center de Physique des Particules de Marseille and director of LSPM for Ars Technica. “Detecting this light allows us to measure the directions and energies of neutrinos.”

sound sensor

The third junction box is devoted to studies of marine sciences, including the so-called Albatross line, which consists of two inductive cables with a length of one kilometer fixed to the ocean floor. These cables carry sensors to measure water temperature and ocean currents, as well as oxygen and pH levels.

the Geoazur Lab, an institute of geosciences located near Cannes, has developed a broadband seismograph that is embedded in sediments on the ocean floor, allowing seismic data to be obtained in real time. Along with a seismograph, the Geoazur researchers have converted one of the optical fibers of the main 42-kilometer photovoltaic cable into a giant array of Seismo-acoustic sensors.

An artist's view of the LSPM underwater platform, anchored at a depth of 2,450 metres.

An artist’s view of the LSPM underwater platform, anchored at a depth of 2,450 metres.

Camille Combs, Overpoit Agency

These are not traditional sensors but defects in the glass that appear during the manufacture of optical fibers. These defects are found in the optical fiber network. This is due to the heating and drawing processes of the glass. As a result of these defects, part of the light is sent back toward the transmitter,” said Anthony Sladen of the Geoazur Lab. He added that a seismic or sound wave either stretches or contracts the optical fiber, thus changing the path of the light within it. “By measuring this change, we can measure both seismic and sound waves.”

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Sladin and his team have transformed the flaws in the glass lattice into 6,000 virtual sensors that can provide data on earthquakes, underwater noise from ships, and waves in real time.

Other devices consist of a group of hydrophones that can detect and record the sounds of whales and dolphins at different frequencies. The data will help scientists understand how often these cetaceans repeat location, as well as their vocal behaviour.

More is coming

While the aforementioned devices are in operation, other laboratory devices, which are already installed on the ocean floor, are expected to be operational by the summer.

Most notable among them is a robot called BathyBot, developed by the Mediterranean Institute of Oceanography, which can move around the ocean floor thanks to caterpillar tracks. The BathyBot is equipped with sensors to measure temperature, oxygen and carbon dioxide concentrations, current velocity and direction, as well as salinity and particle concentration.

BathyBot on BathyReef during tank tests.

BathyBot on BathyReef during tank tests.

Dorian Gilliman, Ohio State University Pythias

Controlled from shore and directed by a built-in camera, the robot will also be able to climb a two-meter-high artificial reef and measure water properties off ocean floor sediments.

Other instruments such as a gamma spectrometer to monitor levels of radioactivity and a single-photon stereo camera to measure the bioluminescence of deep-sea organisms are expected to start operating around the same time frame.

According to Coyle, because the deep sea is not well understood, “facilities like the LSPM can advance our understanding of many different phenomena.”

“The main thing to study is the long-term impact of global warming. The LSPM observations already indicate a rise in sea temperature and lower oxygen levels even at these depths.

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Dhananjay Khadilkar is a journalist based in Paris.