The objective of the multidisciplinary project TONGA is to study the control of ocean productivity and carbon sequestration by micronutrients of hydrothermal origin. At the end of the TONGA cruise (autumn 2019, RV L'Atalante), after having studied the biogeochemical processes and stocks, we left 4 sample collection instruments on a mooring line whose data will allow us to complete an annual cycle of the export of the material towards the bottom, to characterize the biological content and chemical composition and thus to quantify the fluxes of the different fractions.

• The first objective of the TONGA RECUP campaign was to recover the fixed mooring launched on 1/12/2019 during the TONGA campaign, (position: 20°42.408 S / 177°52.128). The 4 instruments on the mooring line closed automatically once the last sample collected on 1/11/2020. The recovery date was conditioned by this.
• The 2nd objective of the TONGA RECUP campaign was to reoccupy 3 stations that were sampled one year earlier (TONGA campaign) in order to refine the delta 15N budget necessary for the interpretation of some mooring results: 2 stations in the Lau basin, close to the mooring and under the expected influence of shallow hydrothermal fluids and a more distant station that will be able to serve as a reference that will be little or not influenced by the emissions of the shallow underwater volcanoes of the TONGA Arc.