Large impact of Stokes drift on the fate of surface floating debris in the South Indian Basin

Delphine Dobler , Thierry Huck (1) , Christophe Maes (2) , Nicolas Grima (1) , Bruno Blanke (2) , Elodie Martinez (2) , Fabrice Ardhuin (3)

1 LPO - Laboratoire de physique des océans
2 LOPS - Laboratoire d'Océanographie Physique et Spatiale
3 HOM - Division Hydrographie Océanographie et Météorologie Militaire

In the open ocean, floating surface debris such as plastics concentrate in five main accumulation zones centered around 30 • latitude, far from highly turbulent areas. Using Lagrangian advection of numerical particles by surface currents from ocean model reanalysis, previous studies have shown long-distance connection from the accumulation zones of the South Indian to the South Pacific oceans. An important physical process affecting surface particles but missing in such analyses is wave-induced Stokes drift. Taking into account surface Stokes drift from a wave model reanalysis radically changes the fate of South Indian particles. The convergence region moves from the east to the west of the basin, so particles leak to the South Atlantic rather than the South Pacific. Stokes drift changes the South Indian sensitive balance between Ekman convergence and turbulent diffusion processes, inducing either westward entrainment in the north of the accumulation zone, or eastward entrainment in the south.

Mots clés: Marine debris; Microplastics; Stokes drift; Indian Ocean; Lagrangian analysis; Ocean surface pathways

Domaines: Océan, Atmosphère

Delphine Dobler, Thierry Huck, Christophe Maes, Nicolas Grima, Bruno Blanke, et al.. Large impact of Stokes drift on the fate of surface floating debris in the South Indian Basin. Marine Pollution Bulletin, 2019, 148, pp.202-209. ⟨10.1016/j.marpolbul.2019.07.057⟩. ⟨hal-02323408⟩