Particles sinking from the surface to the deep ocean play a key role in the biological carbon pump, of which efficiency depends on their concentration and sinking velocities. Over the last decade, in situ imaging has enabled critical advances in the quantification of vertical carbon fluxes. Yet, in situ velocity measurements are scarce and often limited to the bulk population of particles only. Here, we introduce the VisuTrap, consisting of an Underwater Vision Profiler 6 camera inserted in a cylindro-conical sediment trap which isolates a water volume. This system was attached to a sediment trap free-drifting line for 2-day quasi-lagrangian experiments at 2 sites in the Mediterranean Sea. High frequency image acquisition (1.3 Hz) allows reconstruction of a few hundred particle tracks and estimation of their in situ velocities. Images are continuously recorded throughout 42h-long lagrangian cycle, giving an unprecedented overview of particle fluxes temporal dynamics. In the studied area, particles covering a size range from 600 µm to 2 mm sink at a speed up to 1000 m d^-1, with an average of 200 m d^-1. We observed a substantial, yet variable, proportion of suspended and ascending material, for which we hypothesize that biological activity modifies the normal sinking behavior of particles. First analyses show weak yet significant link with several particle morphological properties, suggesting that particle sinking behavior results from multiple factors. Thus, these patterns should be kept in mind when deriving carbon fluxes from particle size spectra and bulk concentration only.

Primary Presenter: Manon Laget, LOG, Laboratoire d’Océanologie et de Géosciences, Université du Littoral Côte d’Opale, Université de Lille, CNRS, IRD, UMR 8187, Wimereux, France (manon.laget@univ-littoral.fr)

Authors:

Manon Laget, LOG, Laboratoire d’Océanologie et de Géosciences, Université du Littoral Côte d’Opale, Université de Lille, CNRS, IRD, UMR 8187, Wimereux, France  (manon.laget@univ-littoral.fr)

Marc Picheral, Sorbonne Université, Centre National de la Recherche Scientifique, Laboratoire d’Océanographie de Villefranche (LOV), Villefranche-sur-Mer, France  ()

Camille Catalano, Sorbonne Université, Centre National de la Recherche Scientifique, Laboratoire d’Océanographie de Villefranche (LOV), Villefranche-sur-Mer, France  ()

Lionel Guidi, Sorbonne Université, Centre National de la Recherche Scientifique, Laboratoire d’Océanographie de Villefranche (LOV), Villefranche-sur-Mer, France  ()

Tristan Biard, LOG, Laboratoire d’Océanologie et de Géosciences, Université du Littoral Côte d’Opale, Université de Lille, CNRS, IRD, UMR 8187, Wimereux, France  ()