Using submarine telecom cables to monitor water temperature and currents between the Islands of the Guadeloupe archipelago
Lannion, France, June 27, 2025
A 10-day scientific mission has just been completed in Guadeloupe. Geologists from the French National Centre for Scientific Research (Geo-Ocean, Brest) and the University of the French Antilles (Pointe-à-Pitre), in collaboration with the Guadeloupe Region, Orange, and IDIL by Fiber Optics Group (a company based in Lannion), have been working for three years on the submarine telecom cables linking the islands of the Guadeloupe archipelago.
Using an optical technique (laser reflectometry), they can detect changes in seawater temperature and mechanical strain on the cables — likely caused by underwater currents. The team has observed seasonal temperature variations (between 27°C and 30°C) and a significant warming on the southern reef platform of Grande-Terre (Saint-François), with an increase of around 1.5°C between 2022 and 2024. This rise in temperature matches recent coral bleaching episodes seen in Guadeloupe’s reefs over the past two years.
Until now, these measurements were taken every 3 to 6 months from roadside cabinets acting as fiber relays. Thanks to support from telecom operator Orange, continuous measurements have been running since June 2025 in Saint-François, every three hours, and will continue for the next 18 months. Good news: the latest data shows that the high water temperatures recorded in 2024 have dropped — back to levels seen in June 2022. (Images of the interrogator installed at Orange’s technical site in Saint-François are available.)
To validate and calibrate the laser reflectometry data, the scientific team, with support from the National Nature Reserve of Petite Terre, has deployed three instruments (temperature sensors and current meters) on the seafloor between Saint-François and La Désirade, right next to the telecom cables. Two more instruments will be added in the coming weeks. These sensors will record data every 30 seconds for one year. Divers installed them at depths ranging from 13 to 25 meters, and they will be retrieved in June 2026. (Photos and underwater footage of the deployment are available.)
