Séminaire
The vertical transport of surface water and carbon into ocean's interior, known as subduction, is one of the main mechanisms through
which the ocean influences Earth's climate. Although subduction has been traditionally associated with the large-scale circulation, both
new instrumental approaches and high-resolution models show the occurrence of localised and intermittent subduction episodes. Some of these studies also revealed the importance of such events on both the formation of mode water and the export of organic matter (the so-called ‘eddy-pump’). However, the evaluation of episodic subduction at a basin-scale is hindered by its transient and localised nature. In this work, we present an approach to detect subduction events at a synoptic scale using measurements collected by biogeochemical autonomous profiling floats (bgcArgo) in the Southern Ocean. Events are detected from anomalies in spiciness and Apparent Oxygen Utilisation in the mesopelagic zone (~100 to 1000m). The spatial distribution of events suggest that injections only occurred in localised hotspots, where intense submesoscale circulation persist. Moreover, injection events were found for less than 1% of the bgcArgo database (~7,000 profiles). Such a low occurrence challenges precedent estimates of eddy-pump contribution to carbon export in the Southern Ocean. However, the localised and efficient vertical transport associated with this mechanism may have important consequences on sustaining mesopelagic ecosystems.
julien.brajard@upmc.fr