Title: Transport of marine debris (and other buoyant material): From upper ocean turbulence to Delaware Bay

Abstract: Microplastic marine debris is widely distributed in vast regions of the ocean and has emerged as a major ocean pollutant. We consider the transport by ocean currents of buoyant material such as marine debris, marine organisms, and spilled oil. We first examine turbulent mixing and transport of buoyant material in the ocean surface boundary layer (OSBL) to show that wave-driven Langmuir turbulence deeply submerges marine debris. We then explore the mean horizontal transport of buoyant material in the OSBL, which is commonly assumed to be accomplished by horizontal mean currents. However, surface convergence zones due to OSBL turbulence organize wind-driven horizontal currents in turbulent jets and near-surface concentrated buoyant material in windrows. This results in a correlation of turbulent jet flow and higher material concentrations and, thus, in a net mean horizontal transport due to turbulent motion. Finally, we investigate microplastics and related transport in the Delaware Bay estuary. We observe that microplastics are ubiquitous in Delaware Bay with concentrations that typically exceed those in the open ocean. In the estuary, buoyant material quickly aggregates in narrow regions that extend several kilometers along the estuary. We explore a Lagrangian convergence mechanism due to tidally driven Lagrangian residual circulations that is efficient in forming such persistent aggregation regions. Our research contributes to better understanding the spatiotemporal distributions of marine debris and other buoyant material.