How Viscoelastic Properties of Colloids, Transparent Exopolymeric Particles and Marine Organic Aggregates, Modify Turbulence and Plankton Biodynamics in the Sea

Abstract

Measurements of viscoelasticity, have already been made using Couette geometry, in the sea itself (See Jenkinson et al, this volume), in ≈1m³ mesocosms, and in phytoplankton suspensions and cultures. These measurements show that the sea is generally a hierarchically lumpy gel, with excess viscous moduli (i. e. in excess of that due to the aqueous phase) and elastic moduli strongly correlated with the quantity of phytoplankton present (measured as chlorophyll content). Formation of these gels starts mainly from colloidal (sub-micrometer) molecules (Gentien, 1995), much of which is probably secreted by phytoplankton. Because they are sticky, they flocculate in deforming water to form Transparent Exopolymeric Particles (TEP - 1 to ≈100 μm) (Mari & Kiørboe, 1996). These TEP are fractal organic aggregates that then flocculate further by sticking to each other and sometimes also to fibres and other biological debris (Mari & Kiørboe, 1996). They are also colonised by bacteria. By these means they can form visible gels (Chin et al, 1998), organic aggregates of size several ≈m to mm (Kiørboe & Hansen, 1993; Worm & Søndergaard, 1998), or even metres in the northern Adriatic (Malej & Harris, 1993; Malej et al, this volume).