Plastic and floating debris in the ocean are a major threat for the ocean life and more generally for the whole planet and its inhabitants.
LARGE SCALE :
We have conducted so far different works at different scales, but the general idea remains the same : understanding the path and the fate of plastic and floating debris at the different oceanic scales (basin, coastal region, ...)
A first study has been conducted for the whole mediterranean basin, using the numerical configuration NEMO-MED12 at 1/12 of a degree for the horizontal resolution.
This work has been conducted during the PhD of J.Mansui, that A. Molcard and myself have supervised. For this study, the approach has been mainly numerical, due to the evident lack of observations at the scale of the mediterranean basin.
However, the study has been completed with numerous but scattered observations to validate and confirm the results obtained. Most of the information about the numerical experiment can be found in J. Mansui's PhD and associated articles (see bottom of the page).
The figure below is a simplified version of the results obtained : at large scale, no permanent areas of debris concentrations have been found, but 3 zones (A,B and C on the figure below) have been identified as potential zones
of accumulation, always restricted in time (around 3 months) due to the important variability of the circulation throughout the year. In addition, some exposed zones for
debris stranding have been identified (red coast lines).
This first work has then been continued, following a downscaling methodology, in order to get information on the floating debris transport at different scales, from the large scale (study above)
to the regional scale and the coastal scale (below).
REGIONAL SCALE :
This study has been conducted at a local scale, using NEMO-GLAZUR64 (see regional dynamics pages for more information on the numerical configuration),
a regional configuration of the north-western mediterranean region at a kilometric resolution (on the horinzontal).
The numerical data have been confronted to field observations collected during two years. The results are in the process of publication but the image below shows one important result :
at the mesoscale, it appears that the model and the observations show that the accumulation areas are mainly on the external border of the Northern current, at the frontal zone
Map of floating marine litter distribution observed along the French Riviera during the EcoOcean cruises (October 2006 - October 2008).
Coloured circles mark the positions and dates of shipboard surveys. Debris densities are broken down in two categories in order to highlight the position of high values:
low densities (less than 10 items/km2, small circles) and high densities (more than 10 items/km2, large circles). The NC general path was determined from GLAZUR64 surface mean velocity fields.
COASTAL SCALE :
For the work and the experiment at coastal scale, see the CADOR project.
MIXING LOCAL AND GOBAL SCALE : 7E CONTINENT EXPEDITION
More recently, I have joined the scientific team of the 7e continent expedition .
The main scientific goal is to sample plastic, micro-plastic to nano-plastic at the sea surface and in the water column to assess its worldwide distibution and also to understand the fate of the passive material on the vertical axis (vertical dynamics).
The next mission should be in the South Atlantic Basin, and the aim will be to track cyclonic and anticyclonic meso-scale eddies to sample their plastic content at the surface and water column.
The figure below shows, for a zoom of the targeted area, the sea surface height (SSH) during 2016 , modeled by a global NEMO configuration at 1/12 fo a degree, developped by Mercator-Ocean .
Mansui J. , Molcard A., Ourmieres Y., Galgani F. and Poitou I. Transport of floating marine litter along the French Riviera. Journal of oceanography