Influence of (sub)mesoscale processes on the distribution of organic and inorganic particles in the South-Eastern Bay of Biscay.

Supervisors: Ainhoa Caballero, Anna Rubio (AZTI).
Mesoscale dynamics have a determinant role in several ocean processes, not only in the transport of momentum, heat and mass, but also in the provisioning of nutrients into the euphotic zone, as well as marine floating litter accumulation. However, this relation is not that straight forward in coastal areas. In the south-eastern sector of the Bay of Biscay, the slope current interacts with the abrupt bathymetry and frequently triggers the formation of mesoscale eddies. In this context, the ETOILE campaign surveyed the CapBreton canyon area in the South-East of Bay of Biscay in early August 2017. The main objective of this campaign was to gather hydrographic and hydrodynamic data, and determine the influence of mesoscale processes in the distribution of organic (phytoplankton) and inorganic (floating marine litter) particles. Besides the various remote sensing data available for this area, such as High Frequency radar or satellite data, in situ discrete hydrographic measurements were collected by a CTD and a Moving Vessel Profiler. Likewise, multi-spectral fluorescence casts, chlorophyll-a, as well as marine floating litter abundance were sampled in selected stations. In addition, other parameters such as temperature, conductivity and in vivo multi-spectral fluorescence were continuously recorded. Here we present the results from a joint analysis, where two cyclonic and two anticyclonic structures were observed. From our observations, we discuss on the differential effect that the two type of (sub)mesoscale eddies exerted in the particle distribution. While cyclones seem to actively accumulate floating marine litter in surface, anticyclones promote primary production below the pycnocline, following a two-step process. First, nutrients upwell at anticyclone’s periphery and then the associated phytoplankton is advected to the core of the structure, which is composed mainly of Brown Algae suggesting a fluid dynamical niche. The presented results might add a new sight in the framework of sustainable recollection of floating marine litter as well as the (sub)mesoscale influence in boosting and modulating the phytoplanktonic community in the south-eastern sector of the Bay of Biscay.