Exchange of Plankton, Pollutants, and Particles Across the Nearshore Region.

Exchange of material across the nearshore region, extending from the shoreline to a few kilometers offshore, determines the concentrations of pathogens and nutrients near the coast and the transport of larvae, whose cross-shore positions influence dispersal and recruitment. Here, we describe a framework for estimating the relative importance of cross-shore exchange mechanisms, including winds, Stokes drift, rip currents, internal waves, and diurnal heating and cooling. For each mechanism, we define an exchange velocity as a function of environmental conditions. The exchange velocity applies for organisms that keep a particular depth due to swimming or buoyancy. A related exchange diffusivity quantifies horizontal spreading of particles without enough vertical swimming speed or buoyancy to counteract turbulent velocities. This framework provides a way to determine which processes are important for cross-shore exchange for a particular study site, time period, and particle behavior. Expected final online publication date for the Annual Review of Marine Science , Volume 15 is January 2023. Please see https://www.annualreviews.org/page/journal/pubdates for revised estimates.