LSCE- UMR CEA-CNRS-UVSQ – Gif sur Yvette – France

B. Bombled, C. Rabouille

The exploration of the deep ocean - one of the least known environments on our planet- is a great challenge for the XXI century -. Understanding the distribution, abundance and dynamics of particulate organic matter (OM) and living organisms in the deep environment, over time and space, is crucial for describing and predicting ecosystem dynamics. This includes understanding the cycle of its major substrate, biogenic carbon, and documenting the response of ecosystems to anthropogenic disturbances. It is also essential to constrain the sequestration of OM in deep sediments on a millennial scale, in view of its role in the regulation of carbon fluxes and global change. To answer these questions, the scientific community has for some years been developing oceanographic, deep-sea and coastal observatories, both fixed and mobile, often cabled, such as the Station Benthique of the Laboratoire des Sciences du Climat et de l'Environnement (LSCE - French joint research unit CEA-CNRS-UVSQ) in Gif-sur-Yvette, or the semi-autonomous benthic robot BathyBot, from the Institut Méditerranéen d'Océanologie (M. I.O) in Marseille, and implemented by the CNRS Technical Division (DT INSU - French Centre National de la Recherche Scientifique) in La Seyne sur Mer.

The “BathyBot” remote-controlled robot is deployed at a depth of 2500 m, 40 km from Toulon (Mediterranean Sea - France), connected the MOOSE/ANTARES cable station as part of the EMSO ERIC (European Multidisciplinary Seafloor and water column Observatory) infrastructure. This benthic robot will complement the ALBATROSS-MII (Autonomous Line with a Broad Acoustic Transmission for Research in Oceanography and Sea Sciences) pelagic instrumented line, equipped with oceanographic sensors. With its mobility, sensors, analyzers and cameras, this crawler-mounted robot opens the way to adaptive monitoring strategies, enabling the acquisition of real-time, long-term observations of the deep-sea environment around strategic points. On-board sensors for temperature, dissolved oxygen, current speed and direction, salinity, turbidity are mounted, together with a camera for acquiring images of deep-sea benthic and pelagic fauna, with sufficient sensitivity to detect bioluminescent organisms.

In this context, the LSCE, in collaboration with the CNRS Technical Division, was asked to install a benthic profiler (Bathy-prof) on the robot, equipped with 6 OXB50-HS-SUB micro-optodes from PyroScience, connected to the PICO-O2-SUB opto-electronic-card, capable of measuring oxygen micro-profiles at the water-sediment interface, a zone of high concentration of organic matter on the seafloor, giving access to the benthic use of organic substrates necessary for the ecosystem metabolism. This profiler will provide a link with measurements of carbon fluxes in the water column and metabolism in the bottom water. It will enable variations in benthic metabolism to be quantified in relation to visual observations obtained by cameras and physico-chemical measurements.

CNRS funding for this profiler, now nearing completion, has enabled us to seize the opportunity to add a major functionality to the BathyBot robot, in order to study early diagenesis in the deep Mediterranean. This Bathy-Prof profiler is also the forerunner of the next deep profiler, also equipped with OXF50-CV PyroScience micro-optodes, being developed as part of the DeepSea'Nnovation project, which benefits from French government funding managed by the National Research Agency (ANR) under the future investment program integrated into France 2030 (ANR-21-ESRE-0042).