Tracer Exchange Across the Stratified Inner‐Shelf Driven by Transient Rip‐Currents and Diurnal Surface Heat Fluxes

Abstract

AbstractExchange across the surf‐zone and inner‐shelf affects coastal water quality and larval recruitment. Surf‐zone generated transient rip‐currents (TRC) exchange shoreline released tracers onto and across a stratified inner‐shelf. Surface heat fluxes (SHF) modify inner‐shelf stratification and surf‐zone temperature, relative to the inner‐shelf, inducing nearshore thermally driven exchange. The coupled effect of TRC and diurnal SHF forcing on cross‐shore exchange is evaluated using idealized model surf‐zone tracer releases with TRC‐only, SHF‐only, and combined SHF+TRC forcing. For conditions representing Fall in Southern California, the TRC mechanism dominates cross‐shore exchange, relative to SHF, to 12LSZ offshore (LSZ = 100 m is the surf‐zone width). Tracer and velocity derived estimates of exchange velocity indicate that the TRC cross–inner‐shelf exchange mechanism is due to an alongshore mean baroclinic flow setup by TRC vertical mixing of inner‐shelf stratification.