Fluid motion and solute distribution around sinking aggregates I : Small-scale fluxes and heterogeneity of nutrients in the pelagic environment
Individ- og populationsinteraktioner
Authors
Kiørboe, Thomas
Ploug, H.
Thygesen, Uffe Høgsbro
Technical University of Denmark,
National Institute of Aquatic Resources,
Section for Ocean Ecology and Climate
unknown
Technical University of Denmark,
National Institute of Aquatic Resources,
Section for Population Ecology and Genetics
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Abstract
Marine snow aggregates are sites of elevated biological activity. This activity depends on the exchange of solutes (O- 2, CO2, mineral nutrients, dissolved organic material, etc.) between the aggregate and the environment and causes heterogeneity in the distribution of dissolved substances in the ambient water. We described the fluid flow and solute distribution around a sinking aggregate by solving the Navier- Stokes' equations and the advection-diffusion equations numerically. The model is valid for Reynolds numbers characteristic of marine snow, up to Re = 20. The model demonstrates the importance of a correct flow environment when making biological rate-measurements on aggregates (e.g., oxygen consumption/production, growth rates of bacteria and phytoplankton) because both solute fluxes and internal solute concentrations depend strongly on the flow environment. Observations of flow and oxygen-concentration fields in the vicinity of both artificial and natural oxygen-consuming aggregates that are suspendedin a flow compare well with model predictions, thus suggesting that our set-up is suitable for making biological rate measurements. The sinking aggregate leaves a long slender plume in its wake, where solute concentration is either elevated (leaking substances) or depressed (consumed substances) relative to ambient concentration. Such plumes may impact the nutrition of osmotrophs. For example, based on published solubilization rates of aggregates we describe the amino acid plume behind a sinking aggregate (0.1 to 1.0 cm radius). The volume of the plume with amino acid concentrations high enough to significantly affect bacterial uptake rates is ca 100x the volume of the aggregate itself. Thus, sinking aggregates may create significant microniches also for free-living bacteria.
Note
Copyright (2001) Inter-Research
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Additional information
Document type:
Journal article. Indicators: Scientific; Peer review. Language: English
ID:
2e3513e4-749b-41d5-8d21-ea09c188110c
Data provider:
Technical University of Denmark
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