Fine scale frontal structure and biological response in an ring-eddy dipole in the Mozambique Channel

Abstract

<p>Located in the southwest Indian Ocean, between Madagascar and the African continent, the Mozambique Channel is a western boundary current system characterized by an intense eddy activity, increasing over the long term (Backeberg et al. 2012). Large anticyclonic rings reaching up to 300 to 350 km in diameter and 2000 m of vertical extension are structuring the marine ecosystems from phytoplankton to top predators (de Ruijter et al., 2002; Ternon et al., 2014, Weimerskirch et al., 2004). They impact the environmental conditions on the Mozambican shelves by promoting the upwelling of rich deeper waters (Lamont et al., 2010; Malauene et al, 2014). Coastal waters, generally rich in plankton and nutrients, can be also be transported offshore along the edges of the rings. The presence of an eddy dipole with the anticyclonic ring in the northern side of the cyclonic eddy can enhance the processes (Roberts et al., 2014). Theses eddy fluxes are supposed to be the dominant source of nutrients for the central Mozambique Channel (Jose et al., 2016). In the context of the RESILIENCE campaign in April-May 2022, we recently observed at fine scale the frontal system of a filament between a Mozambique Channel Ring and a cyclonic eddy in the central Mozambique Channel. Here we present the mean structure, the fine scale processes and the biological evolution. This underlines the importance of mesoscale and sub-mesoscale ocean dynamics for the ecology of the Mozambique Channel and it's evolution.</p>