Abstract
ABSTRACTThe velocity of settling particles is an important determinant of distribution in extinct and extant species with passive dispersal mechanisms, such as plants, corals and phytoplankton. Here, we adapted dynamic scaling, borrowed from engineering, to determine settling velocity. Dynamic scaling leverages physical models with relevant dimensionless numbers matched to achieve similar dynamics to the original object. Previous studies have used flumes, wind tunnels or towed models to examine fluid flow around objects with known velocities. Our novel application uses free-falling models to determine the unknown sinking velocity of planktonic Foraminifera – organisms important to our understanding of the Earth's current and historic climate. Using enlarged 3D printed models of microscopic Foraminifera tests, sunk in viscous mineral oil to match their Reynolds numbers and drag coefficients, we predicted sinking velocity of real tests in seawater. This method can be applied to study other settling particles such as plankton, spores or seeds.
Highlights
The transport of organisms and biologically derived particles through fluid environments strongly influences their spatiotemporal distribution and ecology
While dynamically scaled models have previously been employed to study a number of problems in biological fluid mechanics (e.g. Vogel et al, 1973; Vogel, 1987, 1994; Koehl, 2003), the study of freely falling particles of complex shape – for which settling speed is the key unknown parameter – presents a unique challenge to experimental design that we overcome in this work
While there are more than 30 extant species and over 600 species in the fossil record, settling velocities are known for only 14 species of foraminifera (Fok-Pun and Komar, 1983; Takahashi and Be, 1984; Caromel et al, 2014: 3.41×10−4 to 6.8×10−2 m s−1, Reynolds number (Re)≈18–55)
Summary
The transport of organisms and biologically derived particles through fluid environments strongly influences their spatiotemporal distribution and ecology. Vogel et al, 1973; Vogel, 1987, 1994; Koehl, 2003), the study of freely falling particles of complex shape – for which settling speed is the key unknown parameter – presents a unique challenge to experimental design that we overcome in this work. Engineering problems such as aircraft and submarine design often are approached using scaled-down models in wind tunnels or flumes to examine fluid flows around the model and the resulting fluid dynamic forces it is subjected to. While there are more than 30 extant species and over 600 species in the fossil record, settling velocities are known for only 14 species of foraminifera (Fok-Pun and Komar, 1983; Takahashi and Be, 1984; Caromel et al, 2014: 3.41×10−4 to 6.8×10−2 m s−1, Re≈18–55)
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