Rheological properties of natural waters with regard to plankton thin layers. A short review

The science of Rheology is painted with a broad brush, and the structure of matter is reviewed from the scales of the electron to those of a manufactured or a biologically produced article. The development of theory and measurements of viscosity and other rheological properties is then reviewed, and it is shown that values have been derived without regard to the scales of most ocean processes. After introducing the scales of length, time and stress, we show how measurements and the young theory of non-compression thalassorheology have developed over the last 25 years or so. Seawater viscosity is comprised of a Newtonian, perfectly dispersed component contributed by the water and salts, plus a non-Newtonian, less well dispersed component due to more or less lumpy organic exopolymeric substances (EPS) derived mainly from phytoplankton. The rheological properties (excess viscosity) may be expressed as an empirical coefficient and three exponents: the first for abundance; the second for dependence of excess viscosity on shear rate; and the third for its dependence on length scale. We also show the conditions (generally speaking, high EPS abundance, low shear stress, and small length scale), where excess viscosity is most often likely to be non-trivial relative to water viscosity.