Coccolith Conundrum: How shape affects sinking and light acquisition

Abstract

I use three simple models to assess the degree to which thickness of the upper element of a coccolith and the height of the connecting stalk influence a coccolithophore’s sinking rate, and ability to acquire light. One generates different coccolith profiles by varying how the same amount of mass is distributed among three stacked cylinders, representative of a coccolith. Another examines the sinking velocity of the coccolithophore as a function of the height of the stalk. Stalk height has a significant effect on the sinking velocity, as it can extend the radius of the coccolithophore and increase drag. The third model, looks at how transmission of light through a coccolith affects the irradiance at the cell surface. The thickness of the top element of the coccolith has a small effect on the transmission of light to the cell surface. Calcite is pretty translucent, especially when considering the thickness of the structure is ~50 nanometers thick. These models are then cross tested to see what is the effect of upper coccolith element thickness on sinking rate and what is the effect of stalk height on transmission. Physics-based models are a good first step in exploring the relative importance of different morphological features.