A Dual-Purpose Submarine Cable for Communication and Science: Monitoring Plate Boundaries and Ocean Health with the Tam-Tam SMART System

Trans-oceanic submarine telecommunication cables have been used since the end of the 19th century to send information rapidly across the ocean. Today their cumulative length has reached 1.5 million km, transporting 99% of all digital data (finance, media, internet, communication) to users across the planet. Thanks to recent technological developments, these submarine cables can now be used simultaneously as scientific observatories, without interfering with telecommunication operations. Their global distribution offers great potential for monitoring the deep ocean environment, which is otherwise difficult and costly to instrument. Owing to the data transfer capacity and power supply provided by the cable, this new type of undersea observatory is able to provide continuous and spatially dense data in near-real time for many years to come. Scientific sensors can be installed all along the cable route, particularly at sites that are difficult to access because of their remoteness or depth.Two types of instrumentation strategy are applied today: the grouping of scientific sensors (temperature, pressure, seismology, requiring electric power) within observation nodes (called ‘SMART’ nodes for ‘Science Monitoring And Reliable Telecommunications’) and/or the use of the optical fiber itself as a scientific sensor along its entire length (‘Distributed Fiber Optic Sensing’).We present the example of the Tam-Tam SMART cable, a submarine observatory project which will be deployed in the SW Pacific between Vanuatu and New Caledonia. This cable will cross the New Hebrides subduction zone, one of the most rapid and active plate boundaries in the world and therefore a major source of natural hazards, posing a seismic and tsunami risk to nearby populations. The Tam-Tam project's SMART nodes will be placed on both sides of the subduction front, close to the zones where earthquakes and tsunamis originate. In addition, two optical fibers will be dedicated to science, allowing us to use the 450 km cable as a series of tens of thousands of sensors. The instrumented cable will continuously monitor the activity of the subduction zone, with data being transferred in real time to earthquake and tsunami regional centers in order  to improve early warning systems. In addition to providing a better understanding of how tectonic plate boundaries work, the system has numerous environmental monitoring applications (temperature, ship traffic, storms/ocean wave intensity, marine mammal calls).