HOPE - How do diazotrophs shape the ocean's biological carbon pump?
From the single cell to the ecosystem
PI : Sophie Bonnet
HOPE's ambition is to study the role of our tropical and subtropical oceans in carbon sequestration, using innovative approaches that examine processes occurring at different spatio-temporal scales.
The website
Our objectives
Our 3 specific objectives are as follows:
- To determine how various diazotrophs aggregate, sink and are remineralised using the SOCRATE automated experimental water column designed for this project,
- To determine the pathways by which organic C derived from diazotrophs is exported to the deep ocean using a pioneering approach combining single-cell isotope analyses, in-depth microbiological characterisation of sinking particles and geochemical balances during seasonal oceanographic campaigns,
- To study how environmental factors control the whole process, from the surface diazotroph community to its final export to the deep ocean, by deploying a state-of-the-art autonomous platform, unique in that it takes synoptic measurements both in and below the euphotic zone at high resolution (hourly/daily).
Our physical strategy: the HOPE-VV project
Physical processes also contribute to carbon storage.
In addition to the gravitational sedimentation of CO, physical mechanisms also transport suspended particles and particles that sink to depth. These include several processes acting on different spatial and temporal scales.
However, unlike the horizontal components of 3D ocean currents, which are generally well known, their vertical components (vertical velocities, VVs) remain largely uncharacterised, even though they influence the transfer of carbon from the surface to the deep ocean. Direct in situ measurement of VVs is currently one of the greatest challenges facing physical oceanography.
To fill this knowledge gap, our physics team has recently developed innovative technologies for directly measuring VV in situ. As part of the HOPE-VV project (PI : Dr Anne Petrenko), we propose to deploy and apply these new methods to add a physical component to the HOPE biogeochemical project.
The HOPE-VV project is funded by AMIDEX
Our study site
The HOPE and HOPE-VV projects will take place at two carefully selected study sites, which are distinguished by the diversity of their diazotrophic communities, trophic regimes and physical conditions.
