A remotely operated lab is taking shape 2.5 km under the sea
In 1962, one of the world's first underwater research laboratories and human habitats was established off the coast of Marseilles, France, at a depth of 10 meters. The Conshelf 1 project consisted of a steel structure that hosted two men for a week.
Now, more than 60 years later, another underwater laboratory is being set up not far from Marseilles, this time to study both the sea and sky. Unlike the Conshelf habitat, the Laboratoire Sous-marin Provence Mediterranee (LSPM) won't be manned by humans. Located 40 km off the coast of Toulon at a depth of 2,450 meters, it is Europe's first remotely operated underwater laboratory.
Physics under the sea
Currently, three junction boxes capable of powering several instruments and retrieving data are at the heart of LSPM. The boxes, each measuring 6 meters long and 2 meters high, are connected to a power system on land via a 42-kilometer-long electro-optical cable. The optical portion of this cable is used to collect data from the junction boxes.
Two of the junction boxes are dedicated to the ORCA section of the Kilometer Cube Neutrino Telescope (KM3NeT). ORCA comprises a three-dimensional array of 2,070 spheres, each containing 31 detectors called photomultiplier tubes. These spheres will be arranged on 115 lines anchored to the ocean floor and held taut by submerged floats. Currently, 15 lines have been installed.
ORCA's twin site, ARCA, is located off the coast of Sicily at a depth of 3,400 meters. Collectively, the ORCA and ARCA sites occupy more than one cubic kilometer of water.
"These gigantic arrays of detectors can detect neutrinos emanating from the Southern Hemisphere sky. On the rare occasions [the neutrinos] interact with water molecules, they produce a bluish flash of light in the darkness of the ocean abyss," Paschal Coyle, director of research at the Centre de Physique des Particules de Marseille and director of LSPM told Ars Technica. "Detecting this light allows us to measure the directions and energies of the neutrinos."
The third junction box is dedicated to marine science studies, including the so-called Albatross line, which consists of two 1-km-long inductive cables anchored to the ocean floor. These cables carry sensors to measure water temperature and sea currents, as well as oxygen and pH levels.
The Geoazur Laboratory, an earth science institute based near Cannes, has developed a broadband seismograph that has been placed in the sediment on the ocean floor, allowing real-time acquisition of seismological data. Besides the seismograph, the Geoazur researchers have transformed one of the optical fibers of the 42-km-long main electro-optical cable into a giant array of seismo-acoustic sensors.
These aren't conventional sensors but rather defects in the glass that arise during the manufacturing of the optical fiber. "These defects exist in the lattice of all optical fibers. This is due to the processes of heating and pulling of the glass. As a result of these defects, some part of the light gets sent back toward the transmitter," Anthony Sladen of Geoazur laboratory said. He added that a seismic or acoustic wave either stretches or shrinks the optical fiber, thereby altering the path of the light inside it. "By measuring this change, we can measure both seismic and acoustic waves," Sladen said.
Sladen and his team have turned the defects in the glass lattice into 6,000 virtual sensors that can provide data on earthquakes and underwater noise generated by ships and waves in real time.
Another instrumentation consists of an array 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 frequent the site, as well as their vocal behavior.
More to come
While the above instruments are operational, the laboratory's other devices, which have already been installed on the ocean floor, are expected to be up and running by this summer.
Prominent among them is a robot called BathyBot, developed by the Mediterranean Institute of Oceanography, which can move on the ocean floor thanks to caterpillar tracks. BathyBot is equipped with sensors to measure temperature, oxygen, carbon dioxide concentrations, current speed, and direction, as well as salinity and particle concentration.
Controlled from the shore and guided by an integrated camera, the robot will also be able to climb a 2-meter-high artificial reef and measure the properties of the water away from the ocean floor sediment.
Other instruments expected to start operating around the same timeframe include a gamma-ray spectrometer for monitoring radioactivity levels and a single-photon stereo camera to measure bioluminescence of deep-sea organisms.
According to Coyle, since the deep sea is poorly understood, "installations such as LSPM can enhance our understanding of many different phenomena."
"A key thing to study is the long-term effect of global warming. The LSPM observations already indicate a rise in sea temperature and decrease of oxygen levels even at these depths," he said.
Dhananjay Khadilkar is a journalist based in Paris.