Or how to understand the sequestration of organic matter in deep sediments over the millennia, in terms of its role in the effects of global change…
B. Bombled, C. Rabouille
The exploration and industrial exploitation of the deep ocean – one of the least-known environments on our planet – for a wide range of resources (oil, gas, fisheries, soon minerals, etc.) raises global concerns about their ecological impacts. 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 effects of global change. In order to answer these questions, the scientific community has for some years been developing oceanographic, deep-sea and coastal observatories, fixed or mobile, often cabled, such as the LSCE benthic station or the semi-autonomous benthic robot (BathyBot, below), from the MIO and implemented by the DT at La Seyne sur Mer.
The “BathyBot”, a remotely controlled robot, is being deployed at a depth of 2,500 m, 40 km from Toulon, near the MOOSE/ANTARES cabled station as part of the EMSO ERIC infrastructure. This benthic robot will complement the ALBATROSS-MII pelagic instrumented line with oceanographic sensors. Thanks to its mobility, sensors, analysers and cameras, this crawler-mounted robot opens the way to adaptive monitoring strategies, enabling the acquisition of observations in real time and over the long term, around strategic points in the deep marine environment. On board will be sensors for temperature, dissolved O2, current speed and direction, salinity and turbidity, and 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 DT INSU, has been asked to install a benthic profiler (Bathy-prof) on the robot, equipped with micro-optodes, capable of measuring oxygen micro-profiles at the water-sediment interface, a zone of major concentration of organic matter on the ocean floor, which will provide access to the benthic use of carbon substrates necessary for the metabolism of the ecosystem observed. This profiler will provide a link with measurements of carbon flux in the water column and metabolism in the bottom water. It will quantify the variations in this benthic metabolism in relation to the visual observations obtained by the cameras and the physico-chemical measurements.
Funding from the DIIRO (CNRS) for this profiler, currently being completed at the DT INSU, 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.