Oceanographic implications of non-newtonian properties found in phytoplankton cultures

Abstract

Bulk Theological properties of sea water sometimes change in phytoplankton blooms^1–7, when the water has been described as viscous¹, slimey^2,3, ropey^2–4 or like egg white⁴. Fishing nets have been clogged^2,5,7 and broken², and bubbles⁶ or solids^2,4,5 have been trapped. Turbulent viscosity, however, can be reduced⁸. It has been suggested^1,2,6 that phytoplankton mucus may kill marine animals by ‘clogging’ their gills. Yet oceanographers consider the sea to be newtonian, that is without rigidity and with dynamic viscosity, η, independent of shear rate, γ. I show here that out of eight phytoplankton cultures investigated, η increased with decreasing γ in three, and the highest value of η, found at γ = 0.017 s⁻¹, was ∼400 times that found at unstated but probably high (10²-5 x 10³ s⁻¹) values of γ by Miyaki and Koizumi⁹. Finite values of dynamic rigidity, G′′, were also observed. The characteristic length, L, and time, t, of Kolmogorov eddies¹⁰ are extremely sensitive to simulated γ-dependent η, and as the scales of many oceanic processes depend on L and r, the lack of rheometrical data at ambient γ could be detrimental to the modelling of these processes.