Towards microplastic hotspots detection: A comparative analysis of in-situ sampling and sea surface currents derived by HF radars.

Marine plastic pollution is a global issue affecting ecosystems and various aspects of human life. The scientific community is exploring new monitoring and containment approaches. Because in-situ sampling campaigns are time and resource demanding, there is a focus on integrating different approaches for marine litter monitoring. Data of two in-situ surveys (using a manta net) were compared to sea surface currents data and derived products with the aim to find a proxy variable of the plastic occurrence. Sea surface currents data were provided by the CALYPSO HF network (operating in the Sicily Channel since 2012). Notably, the occurrence of fragment items is inversely correlated with the total kinetic energy (r ~ 0.85). This result was confirmed by a Lagrangian tracking model considering the deployment of virtual drifters around each in-situ measurement point. The proposed method applied to a wider domain using Copernicus Marine Service (CMS) data revealed that high plastic accumulation areas could be located at the centre of eddies often occurring in the winter period. However, uncertainties arise by the moderate-low correlation found between HF CALYPSO and CMS sea current data.