Effects of Mesoscale Dynamics on the Path of Fast-Sinking Particles to the Deep Ocean: A Modeling Study

International audienceThe gravitational sinking of organic particles is a vital component of the biological carbon pump. This sinking process is strongly modulated by the spatiotemporally varying eddy field, complicating the interpretation of particle flux measured by deep-moored sediment traps. By backtracking particles to 200 m depth based on the outputs of a realistic eddy-resolving simulation, we characterize the origins of particles collected at a long-term observatory site in the Northeast Atlantic and focus on the impact of mesoscale dynamics on particle transport. Our results show that mesoscale dynamics between 200 and 1,000 m control the statistical funnel. Over the long term, the horizontal sampling scales of traps are estimated as hundreds of kilometers, with containment radius ranging from 90 to 490 km, depending on sinking velocities. Particle travel time suggests that overall vertical flow acts to facilitate the export, with estimated deviations up to 1 ± 2 days for particles sinking at 50 m d-1 to 1,000 m. Statistical analyses of horizontal displacements reveal that mesoscale eddies at the site confine particle sources in a more local area. On average, particles in anticyclonic eddies sink faster to depth than expected from purely gravitational sinking, contrary to their counterparts in cyclonic eddies. The results highlight the critical role of mesoscale dynamics in determining particle transport in a typical open ocean region with moderate eddy kinetic energy. This study provides implications for the sampling design of particle flux measurements during cruises and the interpretation of deep-ocean mooring observations