Geographical, seasonal, and depth variation in sinking particle speeds in the North Atlantic

Abstract

Particle sinking velocity is considered to bea controlling factor for carbon transport to the deep sea and thus carbon sequestration in the oceans. The velocities of the material exported to depth are considered to be high in high-latitude productive systems and low in oligotrophic distributions. We use a recently developed method based on the measurement of the radioactive pair 210Po-210Pb to calculate particlesinkingvelocitiesinthetemperateandoligotrophicNorthAtlanticduringdifferentbloomstages.Our estimates of average sinking velocities (ASVs) show that slowly sinking particles (<100md 1) contribute significantlytocarbon fluxatallthelocationsexceptinthetemperateregionsduringthebloom.ASVsappear tovarystronglywithseason,whichweproposeiscaused bychanges intheepipelagiccommunitystructure. Our results are the first field datato confirmthe long-standing theorythat particle sinkingvelocities increase with depth, with increases of up to 90% between 50 and 150m depth.