Characterisation of Ocean Currents Off the Port Harcourt Coastline Using Drifter Data

Ocean surface currents are fundamental to understanding the dispersal of pollutants, larvae, and nutrients in coastal marine environments, yet observational data from Nigeria's offshore zone remain sparse. This study characterises the surface current regime off the Port Harcourt coastline, Rivers State, South South Nigeria, using data from six CODE-style surface drifters deployed in the continental shelf waters between January and December 2024. Drifter trajectories are processed to compute Lagrangian velocity statistics including mean current speed, direction, eddy kinetic energy, and diffusivity coefficients. Supplementary Eulerian current measurements from moored acoustic Doppler current profilers at two shelf stations validate drifter-derived current fields. Satellite-derived geostrophic current maps from AVISO altimetry products are compared with in-situ observations to assess the representativeness of satellite data in this coastal domain. The study documents the seasonal reversal of the Guinea Current and the influence of offshore equatorial upwelling on nearshore current patterns. Model-simulated trajectories using the Copernicus Marine Environment Monitoring Service product are validated against drifter tracks to evaluate model skill for operational use in oil spill response. Findings are communicated to the National Oil Spill Detection and Response Agency to improve contingency planning. The study also discusses larval dispersal implications for marine protected area connectivity in the Gulf of Guinea. Keywords: ocean surface currents, drifter data, Port Harcourt, Guinea Current, Lagrangian oceanography