Radon‐222 budget in Catalina Harbor, California: 1. Water mixing rates

Abstract

We describe mixing on the basis of the radon distribution in Catalina Harbor, a small embayment on the southwest side of Catalina Island, California. During June 1998, there was a 2–3‐m‐thick warm surface layer in the inner harbor, underlain by cooler water. A radon budget for this system was constructed with the objective of evaluating boundary fluxes and developing a box model to describe mixing and transport into and within the harbor waters. Benthic inputs were evaluated with in situ benthic flux chambers. Loss via decay and gas evasion was characterized by surveys of radon concentration in the water column. Closure of the budget required another large radon source, which was assumed to be tidal pumping of seawater through beach sands. The budget indicates that inputs were primarily attributable to benthic input (55%) and tidal pumping (38%). Losses were due to evasion to the atmosphere (29%), radioactive decay (35%), and mixing to the open ocean (36%). The average upwelling velocity into surface water was 0.73 m d −1 . Horizontal mixing was parameterized as an eddy diffusion, calculated to be 0.54 ± 0.19 m 2 s −1 , which was consistent with mixing predictions on the basis of scaling arguments.