A numerical estimate of the plankton-induced sea surface tension effects in a Langmuir circulation

Marine phytoplankton is known to produce surface-active materials as part of its metabolism. The sea surface tension gradient due to the presence of plankton produced surfactants leads to a surface shear stress, commonly known as Marangoni stress, that can be of non-negligible intensity in areas of converging (or diverging) flows, where surface-active material concentrates (or lacks). A natural set-up where this condition can be observed is the Langmuir circulation that establishes in presence of wind and waves and exhibits periodic and permanent areas of alternating convergence and divergence. In the present work we adopt a simplified Large Eddy Simulation model for describing the Langmuir circulation and, by the use of a numerical model previously published, obtain an estimate of the Marangoni stress. The computed Marangoni stress peaks in the converging flow areas to values that are two orders of magnitude higher than in the case of absence of wind burst, previously studied by the authors. Such stress, usually disregarded within the numerical simulations of sea and other basin waters, is in fact capable to modify sensibly the distribution of the ecosystem biological components and should be considered for inclusion in the mathematical modelling.