The effect of mesoscale features on the distribution of planktonic organisms are well documented. Yet, the interaction between these spatial features and the temporal scale, which can result in sudden increases of the planktonic biomass, is less known and not described at high resolution. We targeted a permanent mesoscale front in the Ligurian Sea (NW Mediterranean) that we repeatedly sampled between January and June 2021 using a SeaExplorer glider equipped with a UVP6, a versatile in situ imager. We aimed to resolve mesoscale distribution of plankton and particle distribution during the spring bloom, to assess whether the front was a location of increased concentration of zooplankton, and if it constrained the distribution of particles. During the 5 months, the glider conducted more than 5,000 dives and the UVP6 collected 1.1 million images. We focused our analysis on shallow (300 m) transects, which gave a horizontal resolution of 900 m. About 13,000 images of planktonic organisms were retained. Ordination methods applied to particles and plankton concentrations revealed contrasted periods during the bloom, in which changes in particle abundance and size could be explained by changes in the plankton community. The front had a strong influence on particle distribution, while the signal was not as clear for plankton, probably because of the relatively small number of imaged organisms. This work confirms the need to sample both plankton and particles at fine scale to understand their interaction, a task for which automated in situ imaging is particularly adapted.

Primary Presenter: Jean-Olivier Irisson, Sorbonne Université (irisson@normalesup.org)

Authors:

Thelma Panaïotis, Laboratoire d’Océanographie de Villefranche, Sorbonne Université, CNRS, Villefranche-sur-Mer, France  (thelma.panaiotis@imev-mer.fr)

Antoine Poteau, Laboratoire d’Océanographie de Villefranche, Sorbonne Université, CNRS, Villefranche-sur-Mer, France  (antoine.poteau@sorbonne-universite.fr)

Émilie Diamond-Riquier, Laboratoire d’Océanographie de Villefranche, Sorbonne Université, CNRS, Villefranche-sur-Mer, France  (emilie.riquier@imev-mer.fr)

Lucas Courchet, Laboratoire d’Océanographie de Villefranche, Sorbonne Université, CNRS, Villefranche-sur-Mer, France  (lucas.courchet@imev-mer.fr)

Solène Motreuil, Laboratoire d’Océanographie de Villefranche, Sorbonne Université, CNRS, Villefranche-sur-Mer, France  (solene.motreuil@imev-mer.fr)

Camille Catalano, Laboratoire d’Océanographie de Villefranche, Sorbonne Université, CNRS, Villefranche-sur-Mer, France  (camille.catalano@imev-mer.fr)

Laurent Coppola, Laboratoire d’Océanographie de Villefranche, Sorbonne Université, CNRS, Villefranche-sur-Mer, France  (laurent.coppola@imev-mer.fr)

Marc Picheral, Laboratoire d’Océanographie de Villefranche, Sorbonne Université, CNRS, Villefranche-sur-Mer, France  (marc.picheral@imev-mer.fr)

Jean-Olivier Irisson, Laboratoire d’Océanographie de Villefranche, Sorbonne Université, CNRS, Villefranche-sur-Mer, France  (irisson@normalesup.org)