Bulk-phase viscoelastic properties of seawater relationship with plankton components

Abstract

The viscous and elastic moduli at different shear rates, together with various biological oceanographic properties, were determined in seawater from different hydrological layers in the southern North Sea in June. The biological oceanographic parameters included Phaeocystis and Noctiluca abundances, chlorophyll a level (Chi), bacteria. HNAN and aggregate volume fraction. The plankton was jointly dominated by Phaeocystis sp. and Noctiluca scintillans. Noctiluca abundance showed no correlation with any other biological or viscoelastic parameter, but Phaeocystis abundance correlated strongly. The other biological parameters correlated with Phaeocystis and with each other positively and mostly significantly. Overall, viscoelasticity correlated more strongly with Chi than with any other biological parameter. For non-microlayer samples, the excess complex (viscoelastic) modulus (jiPa) C* E = 2.0 x Chi 1-1 (Chi in mg m J). Viscous and elastic moduli also correlated closely with each other. For a given value of Chi. the microlayer samples were 6.5 or 14 times (depending on the estimation method) more viscoelastic than in bulk-phase samples. Viscoelasticity in samples of settled benthic 'fluff were lower even than bulk-phase samples, but this difference was not significant. Comparison with Mediterranean data on viscoelasticity (Jenkinson. Oceanol. Acta, 16,317-334.1993), using published values for phytoplankton biomass (Wiadnyana,/ Rech. Octanogr., 17,1-6,1992), suggests that the relationship between Chi (or phytoplankton biomass) and viscoelasticity might be general. This apparent biomodlfication of the viscosity and elasticity of seawater is discussed in relation to its likely impact on turbulence and plankton ecology.

Heterogeneity in bacterioplankton abundance from 4.5 millimetre resolution sampling

“…It has been suggested that at the microscale, seawater is an organic matter continuum of tangled polymers and embedded particles (Azam 1998), including transparent exoploymeric particles (TEP) (Alldredge et al 1993), proteinaceous coomassie stained particles (CSP) (Long & Azam 1996), and organic sub-micrometer particles (Koike et al 1990). The potentially gel-like nature of this organic matter continuum (Azam 1998, Chin et al 1998, and the bulk effects of phytoplankton exuded polysaccharides, may act to increase water viscosity and influence turbulent drag by elastic effects (Jenkinson 1986, Jenkinson & Biddanda 1995. Lack of rheometrical data taking into account the non-newtonian properties of seawater could impair the accurate modelling of smallscale oceanographic processes (Jenkinson 1986).…”

Global marine plankton functional type biomass distributions: <i>Phaeocystis</i> spp.

“…DMS has been suggested to play an important role in cloud formation, and DMS production is the main recycling pathway of sulphur from the ocean to the land. Furthermore, Phaeocystis has been well documented as associated with marked increases in seawater viscosity (Jenkinson and Biddanda, 1995;Seuront et al, 2007). In their review, Schoemann et al (2005) conclude that it should be possible to derive a single unique parameterisation of Phaeocystis growth for global modelling.…”

Influence of altered light conditions and grazers on Scrippsiella trochoidea (Dinophyceae) cyst ­formation

“…Due to the mucilage, which often surrounds temporary cysts, they often form clumps or aggregates (Olli 2004). However, Jenkinson & Biddanda (1995) suggest that adsorption of colloidal material, such as dissolved organic material (DOM), onto mucilaginous material could increase the availability of DOM to biological consumers. Seuront & Vincent (2008) demonstrated that high viscosity induced by in creased amounts of mucilaginous material did not mechanically hamper zooplankton grazing.…”