Compared to a low-density spherical particle, a high-density spherical particle of the same size will sink through water at what rate?
The high-density particle will sink at a faster rate.
Stokes' law states that the settling velocity
Thus, for two particles with the same diameter but different densities sinking in the same fluid, the relative sinking rates are
That is, the ratio of their sinking rates equals the square of the ratio of their densities.
The consequence to phytoplankton
Sinking due to gravity is a significant source of mortality for phytoplankton because most cells are slightly denser than water.
Cells with the same size but twice the density as other cells will sink four times as fast.
Thus, the denser cells will need a higher degree of turbulence to persist in the water column.