Tracer Evolution in Multiscale Oceanic Flow Fields

Tracking ocean pollution and marine litter is a compelling problem for safeguarding ocean ecosystems and is recognized as a priority under the UN Ocean Decade Vision 2030. This work investigates how the evolution of pollution transport is affected by ocean dynamics across multiple spatial scales, with particular focus on mesoscale and submesoscale flow structures.

To achieve this goal, high- and very high-resolution regional ocean simulations were conducted in the Subpolar and Tropical Northern Atlantic, two open ocean regions characterized by a different baroclinic deformation radius and therefore different mesoscale eddy sizes. Secondly, different oil spill simulations were performed to understand how submesoscale filaments influence pollutant concentration patterns. Idealized coastlines are considered to perform a statistical analysis of beached oil distributions and particles first-passage time, enabling a direct link between transport pathways and underlying flow properties.

The high-resolution (“child”) ocean fields were obtained by dynamically downscaling the 1/12° (“parent”) Global Ocean Physics Analysis and Forecast product from the Copernicus Marine Service using the SURF platform (v2.0.1), based on NEMO v5.0.1. Horizontal resolutions of 1/36° and 1/108° were achieved, covering the period 1 January–30 June 2025. Each month has been simulated independently to maintain consistency between the parent and child model fields.

The MEDSLIK-II v3.0 software has been used to run multiple oil spill simulations in both the high-resolution and coarse fields. One simulation is run every five days in the period covered by the high-resolution simulations. Each simulation covers ten days and is characterized by a punctual continuous release lasting five days.

Beached oil concentration and first-passage time probability distribution functions were computed and compared across resolutions and dynamical regimes.

The results show that oil concentration distributions associated with highly resolved ocean fields, appear to be characterized by fatter tails and larger concentration extreme values. This indicates that submesoscale activity, better resolved at finer resolutions, enhances surface pollutant aggregation, while coarser simulations tend to underestimate these extremes.