Abstract
Microstructure profiling was utilized to estimate vertical mixing (via vertical turbulent buoyancy flux) during a tidal pulse in the interior Merrimack River plume in calm winds. Multiple stratified shear mixing regimes appear and evolve with time. Initially the plume acts as a nearfield jet, with mixing in the plume (plume layer mixing) and over the plume‐ambient interface (nearfield interfacial mixing). As the plume grows, interfacial mixing is suppressed offshore of the nearfield as currents slow, diminishing turbulent exchange between plume and shelf. At the end of ebb, ambient tidal currents reverse direction below plume, initiating another mode of internal, interfacial mixing (coined here as tidal interfacial mixing), allowing exchange between plume and ambient waters offshore. This work highlights previously unreported tidally modulated mixing within the near and midfield of a river plume.
Turbulence measurements are taken throughout a tidal river plume over an ebb tide. Three mixing regimes related to stratified‐shear processes (vertical differences in density and velocity) are identified: nearfield interfacial, plume layer, and tidal interfacial mixing. Each regime acts over different spatiotemporal scales and vary in importance. Collectively this work highlights previously unknown variability in tidal plume shear mixing processes which control how river‐borne tracers enter the coastal ocean.
Observations taken in a tidal river plume identify three shear mixing regimes: plume layer, nearfield interfacial, and tidal interfacial
The intensity of each regime is quantified via the vertical turbulent buoyancy flux and spatiotemporal evolution is discussed