The MOST project: Monitoring Ocean Seafloor Temperature and currents using fiber optic sensing in shallow shelf seas

Shallow shelf seas (<200 m depth) cover 7% of the ocean’s surface, yet generate 15-20% of global primary productivity and are vital for fisheries, tourism, and coastal economies. However, the sparsity of sub-surface and seafloor observations makes them under monitored, leaving key circulation processes (e.g.- marine heatwaves) poorly constrained. The MOST project aims to bridge this data gap using distributed fiber optic sensing on submarine cables to perform real-time monitoring of water temperature changes, currents and pressure at the seafloor. The first pilot study area is a commercial network of telecom cables in Guadeloupe where an intermittent three-year time series using BOTDR (Brillouin Optical Time Domain Reflectometry) correlates with the Sea Surface Temperature to within 0.1°C and continuous BOTDR monitoring has begun. Building upon this we will perform continuous DAS (Distributed Acoustic Sensing) and deploy in-situ seafloor instruments. The second study area is the macrotidal Bay of Brest, where a prototype hybrid telecom cable (featuring loose and tight sensor fibers) has been deployed enabling a novel method for separating temperature and mechanical strain signals, with potential application to future telecom cables. In both study areas, fiber sensing observations will be cross-validated by oceanographic and seismological instruments deployed next to the cable to calibrate the signals and upscale our technique to other cables worldwide. Starting with commercial cables on the Brittany shelf, we plan to perform L-band DAS interrogation to avoid disrupting internet data transmission. Leveraging the world’s 1.5 million km of submarine cables, MOST can transform the coastal portions into dense arrays of environmental sensors at unprecedented spatial (<10 m) and temporal (<1 hr) scales to better evaluate and anticipate the impact of climate change on the oceans and the seafloor.