Reconciling the size‐dependence of marine particle sinking speed

Sinking particles are critical to the ocean's “biological pump,” sequestering carbon from the atmosphere. Particles' sinking speeds are a primary factor determining fluxes and subsequent ecological and climatic impacts. While size is a key determinant of particles' sinking speeds, observations suggest a variable size-sinking relationship, affected by other particle properties, resulting in substantial spread in parameterizations of particle sinking and fluxes. We compile particle size-sinking observations and apply hierarchical Bayesian statistical models to resolve the size-sinking relationship while accounting for other factors. We find an overall scaling close to the general Navier-Stokes drag equation, and differences between particle types, open ocean versus coastal/laboratory particles, and in situ versus ex situ methods. These results can help harmonize how Earth system models parameterize particle fluxes and support a weaker size-dependence than often assumed, with implications for the flux contribution of small particles and the predicted future shrinking of marine particle populations.