Microhydrodynamics of flotation processes in the sea surface layer

The uppermost surface of the ocean forms a peculiarly important ecosystem, the sea surface microlayer (SML). Comprising the top 1-1000 mum of the ocea n surface, the SML concentrates many chemical substances, particularly thos e that are surface active. Important economically as a nursery for fish egg s and larvae, the SML unfortunately is also especially vulnerable to pollut ion. Contaminants that settle out from the air, have low solubility, or att ach to floatable matter tend to accumulate in the SML. Bubbles contribute prominently to the dynamics of air-sea exchanges, playin g an important role in geochemical cycling of material in the upper ocean a nd SML. In addition to the movement of bubbles, the development of a bubble cloud interrelates with the single particle dynamics of all other bubbles and particles. In the early sixties, several in situ oceanographic techniqu es revealed an "unbelievably immense" number of coastal bubbles of radius 1 5-300 mum. The spatial and temporal variation of bubble numbers were studie d; acoustical oceanographers now use bubbles as tracers to determine ocean processes near the ocean surface. Sea state and rain noises have both been definitively ascribed to the radiation from huge numbers of infant micro bu bbles [The Acoustic Bubble. Academic Press, San Diego]. Our research programme aims at constructing a hydrodynamic model for partic le transport processes occurring at the microscale, in multi-phase flotatio n suspensions. Current research addresses bubble and floc microhydrodynamic s as building blocks for a microscale transport model. This paper reviews s ea surface transport processes in the microlayer and the lower atmosphere, and identifies those amenable to microhydrodynamic modelling and simulation . It presents preliminary simulation results including the multi-body hydro dynamic mobility functions for the modelling of "dynamic bubble filters" an d floc suspensions. Hydrodynamic interactions versus spatial anisotropy and size of particle clouds are investigated. (C) 2001 Elsevier Science B.V. A ll rights reserved.