IN2P3/CNRS
In 1962, one of the world’s first underwater laboratories and human habitats was established at a depth of 10 meters off the coast of Marseille, France. The Conshelf 1 project consisted of a steel structure that housed two men for her week.
More than 60 years later, another underwater laboratory has been established not far from Marseille, this time studying both the sea and the sky. Unlike the Conshelf habitat, the Laboratoire Sous-marin Provence Méditerranée (LSPM) has no permanent human presence. Located 40 km from the coast of Toulon and at a depth of 2,450 meters, it is Europe’s first remotely operated underwater laboratory.
undersea physics
At the heart of the LSPM today are three junction boxes that can power and retrieve data from multiple devices. Each 6-meter-long, 2-meter-high box is connected to the shore power system via a 42-kilometer-long electric-optical cable. The optical portion of this cable is used to collect data from the junction box.
Two of the junction boxes are dedicated to the ORCA section of the Kilometer Cube Neutrino Telescope (KM3NeT). ORCA consists of a three-dimensional array of 2,070 spheres, each containing 31 detectors called photomultiplier tubes. These spheres are placed on 115 lines anchored to the seafloor and held taut by floats in the water. Currently, 15 lines are installed.
Optical detection module of the KM3NeT neutrino detector.
Patrick Dumas/CNRS
ORCA’s twin site, ARCA, is located in 3,400 meters of water off the coast of Sicily. Collectively, the ORCA and ARCA sites occupy more than 1 cubic kilometer of water.
“These giant detector arrays can detect neutrinos emanating from the Southern Hemisphere sky. [the neutrinos] It interacts with water molecules and produces a flash of bluish light in the darkness of the deep sea,” Paschal Coyle, research director at the Marseille Center for Physics and head of the LSPM, told Ars Technica. I’m here. “By detecting this light, we can measure the direction and energy of the neutrinos.”
Sensing sound
A third junction box is dedicated to marine science research, including the so-called Albatross Line, which consists of two 1-km-long guided cables anchored to the seafloor. These cables are equipped with sensors for measuring water temperature and current, as well as oxygen and pH levels.
The Geoazur Laboratory, a geosciences laboratory near Cannes, has developed a broadband seismometer placed in sediments on the seafloor, enabling real-time acquisition of seismic data. In addition to the seismometer, Geoazur’s researchers converted one of his optical fibers in a 42-km-long main electro-optical cable into a huge array of seismic acoustic sensors.
An artist’s perspective of the LSPM underwater platform at a depth of 2,450 meters.
Camille Combes, Open Box Agency
These are not traditional sensors, but glass defects that occur during the manufacture of optical fibers. “These defects are present in all fiber optic gratings. This is due to the process of heating and stretching the glass. As a result of these defects, some of the light is sent back to the transmitter,” he said. says his Anthony Sladen of the Geoazur Institute. He added that seismic or acoustic waves stretch or compress optical fibers, changing the path of light within them. “By measuring this change, we can measure both seismic and acoustic waves,” Sladen said.
Sladen and his team have turned defects in glass grids into 6,000 virtual sensors that can provide real-time data on earthquakes and underwater noise generated by ships and waves.
Another device consists of an array of hydrophones that can detect and record the sounds of whales and dolphins at different frequencies. This data will help scientists understand how often these cetaceans frequent the site and their vocal behavior.
In the future
While the above instruments are operational, the lab’s other instruments, already located on the seafloor, are expected to be operational by this summer.
Standing out among them is a robot called BathyBot, developed by the Mediterranean Institute of Oceanography, which can navigate the seafloor thanks to its caterpillar tracks. BathyBot is equipped with sensors to measure temperature, oxygen, carbon dioxide levels, current speed, direction, salinity and particle concentration.
BathyBot on BathyReef during tank testing.
Dorian Guillemain, OSU Pythéas
Controlled from the shore and guided by integrated cameras, the robot can also climb two-meter-tall artificial reefs and measure water properties away from seafloor sediments.
Other instruments expected to enter operation around the same time include a gamma-ray spectrometer to monitor radioactivity levels and a single-photon stereo camera to measure the bioluminescence of deep-sea organisms. .
Coyle says that the deep ocean is so poorly understood that “a facility like the LSPM can help us better understand a range of phenomena.”
“An important thing to study is the long-term effects of global warming. LSPM observations already show rising ocean temperatures and decreasing oxygen levels even at these depths,” he said. .
Dhananjay Khadilkar is a journalist based in Paris.
