Grands dauphins Grands dauphins à l’étrave du Marion Dufresne © Salomé Pellé

35 days of RESILIENCE in the heart of the Mozambique Channel

The RESILIENCE oceanographic campaign, led by Jean-François Ternon, a researcher from the IRD (Institut de Recherche pour le Développement) and his partners, left Reunion Island on 19 April 2022 and reached the south-western Indian Ocean for 35 days at sea. On board the Marion Dufresne, the legendary ship of the French Oceanographic Fleet, seventy international scientists embarked to better understand the interactions between physics and biology on a small scale in the particular ocean structures of the Mozambique Channel.

Understanding the role of eddies in biological productivity and ecosystem structuring

In the ocean, the role of medium (about 100 kilometres) and small-scale (a few kilometres) physical processes on biological productivity and the structuring of living ecosystems in the open ocean is still poorly understood.
Often well described by numerical modelling but very difficult to observe at sea, these eddy structures and the small-scale processes associated with them play a fundamental role in ecosystems. They contribute to the horizontal and vertical supply and mixing of nutrients, which are key elements for primary production and for strengthening the entire food chain.

navire océanographique Marion Dufresne
Le navire océanographique Marion Dufresne au départ de la Réunion © Christophe Mocquet

Their role is all the more important in already nutrient-poor environments, such as the southwestern Indian Ocean. The Mozambique Channel in particular, an arm of the Indian Ocean separating the island of Madagascar from the rest of Africa, is directly connected to the oceanic region in south-east Africa, which is a major exchange zone between the Atlantic and Indian basins.

This area is the seat of a very complex oceanic circulation characterised by highly non-linear dynamics. The Mozambique Channel is itself criss-crossed by numerous, sometimes giant, eddy “rings”, which are both very distinct and very mobile, and on the edges of which are located highly dynamic fronts.

L’équipe scientifique de la campagne © Christophe Mocquet

It is at these fronts that the physical and chemical exchanges necessary for biological productivity and ecosystems take place. However, in the context of climate change, it is predicted that the intensity of these fronts will vary in the future with possible consequences for ecosystems, general ocean circulation and global climate control. The study of the processes taking place within these oceanic eddy structures is therefore important in order to understand the effects of their future evolution.

Juvénile albatros à nez jaune de l’Océan Indien aperçu très proche du bateau © Peter Ryan

It is in this context that a team of more than seventy international scientists from France (MARBEC, ENTROPIE, LEMAR, LOCEAN, LOG, LOPS, MIO), South Africa (3 universities in Qqeberha, Cape Town, Stellenbosch), Mozambique, the United Kingdom and the United States have embarked on the RESILIENCE oceanographic campaign
Their objective is to criss-cross the geographical area between the centre of the Mozambique Channel and the east coast of South Africa, in an attempt to gain a better understanding of the physical-biological coupling at the level of eddy fronts, and their impact on the various compartments of the marine ecosystem, from plankton to megafauna.

The campaign is partly funded by the Belmont Forum’s Ocean Front Change programme. Other sources of funding are currently the LEFE (CNRS) and ISblue (IUEM) programmes, the French Oceanographic Fleet, and the National Research Foundation (NRF) in South Africa.

A Multidisciplinary Campaign With A Mobile University

In essence, the RESILIENCE campaign is international and highly multidisciplinary. It involves the use of numerous means of continuous observation as well as measurements and samples taken at fixed points.

  • Fine-scale observations are carried out continuously by towing an undulating system of the MVP (Moving Vessel Profiler) and Scan-fish type between the surface and 100 or 300 m depth depending on the instrument, equipped with temperature, salinity, pressure and fluorescence sensors, to observe biological activity.
  • At certain fixed stations, these observations will be supplemented by vertical profiles (CTD type associated with phyto- and zooplankton observations) during which water samples will also be taken (for biogeochemical measurements) at different depth levels. These measurements will be supplemented by plankton net and mesopelagic trawl hauls.
  • On the way and in the station, continuous measurements will complete the system. Surface samples will be used to study the spatial and temporal variation of elements present in the water (micro-nutrients, CO2, fluorescence), while acoustic measurements will be used to characterise currents and the distribution of zooplankton and micronekton (intermediate trophic level).
  • In transit observations of birds and marine mammals as well as plastic waste will also be carried out with the deployment of drones for the sampling of marine mammal breaths.
  • The deployment – and recovery 2 weeks later – of a mooring line is planned off Durban. A second mooring line will be deployed off Bassas de India (one of the Eparses Islands) for a period of one year.

Finally, in addition to their scientific activities on board, the scientists will host a Floating University composed of 21 students and 2 supervisors from the Universities of Bretagne Occidentale (UBO), Littoral Côte d’Opale (ULCO), Côte d’Azur (UCA) and the Nelson Mandela University.

share the article on social media