Consistent Increase in Particle Sinking Velocity with Depth Found across >30 High-Latitude Phytoplankton Blooms using Biogeochemical Argo

The flux of sinking organic particles through the mesopelagic plays a critical role in both global climate and ocean ecosystems. The sinking velocity of these particles is a critical parameter, both for understanding patterns in traditional carbon flux measurements and for calculating carbon flux from the growing array of optical particle measurements. We estimated the bulk sinking velocities of pulses of large (>100µm) particles as a function of depth in the mesopelagic during >30 high-latitude phytoplankton blooms, finding a consistent increase in sinking mean velocity between 200 and 600 m. Our results compare well with a multi-region mean of sinking velocity profiles calculated using analysis of 210Po-210Pb disequilibrium profiles and qualitatively match patterns found in several published studies. These results suggest that the selective loss of slower particles with depth may largely explain the widespread observed power-law dependence of particle flux with depth. This work therefore contributes to mechanistic understanding of the biological carbon pump, and it should improve future optical estimates of particle flux as well.