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摘要
We model how phytoplankton-produced exopolymeric substances (EPS) may change pycnocline thickness delta z through control by Richardson number Ri. Shear stress tau(FORCED) is imposed across the pycnocline, giving a shear rate delta u/delta z, where delta u is cross-pycnocline velocity difference, modulated by viscosity eta. In natural waters, viscosity is composed of two components. The first is Newtonian, perfectly dispersed viscosity due to water and salts. The second is non-Newtonian, and depends on phytoplankton abundance raised to an exponent between +1.0 and +1.5. It is also generally shear-thinning, depending on (delta u/delta z)(P), where P is negative. In suspensions of microbial aggregates, viscosity depends also on (length scale)(d). Published measurements of EPS rheology in a culture of Karenia mikimotoi are input. These measurements were made at 0.5 mm, so they can be scaled to delta u/delta z if d is known for this EPS over the appropriate range of length scales. The model shows that delta u/delta z is very sensitive to d. At values of d <-0.2 or -0.3, however, high concentrations of K. mikimotoi (< 31 million L-1) have no significant effect on delta z at ambient values (> 1 cm). Future investigations of pycnocline dynamics should include measurements of rheological properties, and particularly d.
- 出版日期2011-3
- 单位中国科学院海洋研究所
