Transient Attracting Profiles in the Great Pacific Garbage Patch

A major challenge for cleanup operations in the Great Pacific Garbage Patch is to predict day to day variabilities of plastic concentrations and to identify hotspots of marine debris. An ideal application would indicate material confluence at operational scales O(1 − 10km) but from mesoscale observations of sea surface height O(10 − 100km). The present study introduces the concept of TRansient Attracting Profiles (TRAPs, Serra et al. (2020), Serra and Haller (2016)) to this debate. TRAPs are computable from the instantaneous strain field on the ocean surface and act like short-term attractors for floating objects. Previous experiments have shown the potential of TRAPs to predict pathways of material transport and here we explore the occurrence of these profiles in the North Pacific subtropical gyre, a large-scale convergence zone that is known to entail the Great Pacific Garbage Patch. We compute TRAPs upon daily snapshots of near-surface geostrophic + Ekman current velocity and create a 20-years record of 4,076,065 TRAP objects. We identify 720,391 TRAP trajectories from this data and relate the propagation, persistence and attraction strength of TRAPs to detections of mesoscale eddies. We uncover a life cycle of long-living TRAPs and evaluate recurrent patterns in their vorticity environment. Our study culminates in an unprecedented statistical analysis of drifter motion around TRAPs. We highlight beneficial conditions for hyperbolic transport, estimate local retention times of drifters and find a preference of drifter visits during the formation stage of TRAPs. Our findings provide novel aspects towards mesoscale strain on the ocean surface and how it may benefit search operations at sea.