The contribution of animal-borne biologgers in observing the Southern Ocean physical and biological changes while studying their ecology.

Evidence of climate-change effects on the Southern Ocean (SO) is accumulating. Making up about 10 % of the Ocean surface area, the SO plays a disproportionately important role in the global climate system. It accounts for 75% of uptake of heat excess, 25% of the Ocean’s primary production, and 43% of anthropogenic CO2 uptake. The SO owes two-thirds of its carbon-sequestration capacities to its physical and one-third to its biological pump export of organic carbon. In that context and as part of an international project, over the last twenty years animal-borne satellite data relayed loggers collecting both environmental data and behavioral represent the most significant contribution in documenting changes in the physical properties of the SO in complement to other observational approaches (oceanographic vessels, Argo floats, satellite observations…).

Historically physical parameters: temperature, salinity, light level, wind/sea-state were measured in a first stage, before being completed by the collection of biogeochemical parameters: chlorophyll-a and dissolved oxygen allowing the monitoring of an increasing number of oceanographic parameters critically important to address numerous oceanographic questions. These data are critical in assessing how quickly the SO changing and their ecological consequences on southern elephant seals. Currently, efforts focus on the developments of a new generation of animal-borne sensors dedicated to the assessment of the biological component of the SO, in particular of the poorly known but essential mid-trophic levels, by measuring bioluminescence, echo-sounding and photographing small marine organisms to characterize them. In this talk, we present how this approach contributes to the understanding of how changes in oceanographic conditions could influence the orientation of the SO food webs cascading from phytoplankton to upper marine predators with major expected consequences on the ecological services provided by the SO to humanity.