Microplastic Dispersal in Lake Ontario Driven by Lagrangian Coherent Structures

Abstract The spatial distribution of microplastics in large bodies of water like Lake Ontario depends on the lake's hidden flow patterns. By analyzing a time series of offshore circulation and employing backward Finite-Time Lyapunov Exponent (FTLE) fields along with Lagrangian particle tracking, we find correlations between the Earth's rotation, basin-wide internal waves, and the localized fate of microplastic pollution. Our findings reveal two distinct regimes in pollution transport: a high-speed transport "Southern Conveyor Belt" that acts as a regional transport of plastics, and a low-speed or diffusive spread "Toronto Trap" that serves as a local accumulator of urban waste. Furthermore, Mean Square Displacement (MSD) analysis shows three distinct kinematic transport regimes governing this dispersal: an early-time diffusive regime, an intermediate super-ballistic regime driven by rapid spatial acceleration and shear dispersion into Lagrangian Coherent Structures (LCS), and a late-time ballistic regime reflecting steady advection. This quantitative analysis confirms that particles released from southern sources travel significantly farther distances overall, reinforcing the contrast between the high-transport southern coastal jet and the low-transport northwestern retention zones.