Effects of attached bacteria on organic aggregate settling velocity in seawater

Abstract

We investigated whether attached bacteria affect the settling velocity of organic aggregates via modifications of the physical properties of aggregates, including density, porosity, and morphology. Model aggregates, prepared by mixing 2 different polysaccharides (fucoidan and chitosan), were incubated in coastal seawater passed through either 0.8 μm (AGG 0.8 ) or 0.2 μm (AGG 0.2 ) filters. After incubation for 48 h, AGG 0.8 were much more densely (3.2-to 10.1-fold) colonized by bacteria than AGG 0.2 . Based on median settling velocities (W 50 ), as determined by laser in situ scattering and transmissometry, the W 50 of AGG 0.8 was lower (1.6-to 4.5-fold) than that of AGG 0.2 for a size class of 62 to 119 μm. Stokes model analyses indicated that this reduction in W 50 could be largely attributed to the higher porosities of AGG 0.8 (0.932−0.981) than those of AGG 0.2 (0.719−0.929). Our results support the notion that the modification of aggregate structure by attached bacteria (porosity enhancement) can be an important factor controlling the settling velocity of marine particles.

Fractional iron solubility of atmospheric iron inputs to the Southern Ocean

“…We acknowledge that processes in the ocean can alter sinking rates, such as aggregation of colloids. Moreover, particle dimensions can change, for example with bacterial attachment (Yamada et al, 2013). Labile Fe comprises a large component of total Fe, and this fraction may be slowly released from aerosol particles into the surface mixed layer.…”

Transparent exopolymer particles (TEP) in the deep ocean: full-depth distribution patterns and contribution to the organic carbon pool

“…Largely different prokaryote-TEP relationships between the upper and deep oceans under- score the complexity of interactions between TEP and prokaryotes. Prokaryotes can be a source of TEP as well as consumers (decomposers) of TEP and TEP precursors (Yamada et al 2013, Busch et al 2017. The prokaryotic parameters−TEP relationship may be the net outcome of opposing (i.e.…”

Dynamics and Origin of Transparent Exopolymer Particles in the Oyashio Region of the Western Subarctic Pacific during the Spring Diatom Bloom

“…Heterotrophic organisms such as eubacteria can also be important in production (e.g., Passow, 2002b;Sugimoto et al, 2007), decomposition (e.g., Passow et al, 2001), and transformation (e.g., Gärdes et al, 2011;Yamada et al, 2013) processes of TEP. Although the present study suggests that the main TEP producer was likely phytoplankton as described above, bacteria abundance was significantly correlated with not only TEP concentration but also Chl a concentration.…”