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.

Automated summary

Research shows that sinking particles play a critical role in the ocean's biological pump by sequestering carbon from the atmosphere. However, the sinking speeds of particles are not solely determined by size, but also by other factors, leading to significant variability in parameterizations of particle sinking and fluxes.