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

Abstract

The 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.

Effects of Balanced Motions and Unbalanced Internal Waves on Steric Height in the Mid‐Latitude Ocean

“…The discrepancy in the mooring‐based steric height and altimetry SLA likely stems from the missing contributions of steric height in the top 50 m and the deep ocean (i.e., below 480 dbar) by the moorings, as in the comparison between seal‐based upper‐ocean steric height and altimetry SLA in the Southern Ocean (Siegelman et al., 2020). Although the submesoscale motions in the bottom boundary layer should be rather weak due to flat topography, mesoscale eddies in the study region are found to commonly extend down to about 1,000 m (L. Wang et al., 2022).…”

Structure of the Bottom Boundary Current South of Iceland and Spreading of Deep Waters by Submesoscale Processes

“…(2021); Wang et al. (2022). It is performed using the Coastal and Regional Ocean COmmunity model (CROCO, Shchepetkin & McWilliams, 2005, a version of ROMS model).…”

“…We use outputs of a realistic simulation of the North Atlantic Subpolar Gyre, already used and validated in previous studies, for example, Le Corre, Gula, Smilenova, and Houper (2019); Le Corre, Gula, and Treguier (2019);de Marez & Le Corre (n.d.); Smilenova et al (n.d.); de Marez et al (2021); Wang et al (2022). It is performed using the Coastal and Regional Ocean COmmunity model (CROCO, Shchepetkin & McWilliams, 2005, a version of ROMS model).…”

Deep ocean particle flux in the Northeast Atlantic over the past 30 years: carbon sequestration is controlled by ecosystem structure in the upper ocean

“…These estimates rely on modelled current speeds and assumed particle sinking speeds; the latter entails considerable uncertainty. A particle tracking modelling study at PAP-SO by Wang et al (2022) concluded that mesoscale dynamics between 200 and 1,000 m depth control the dimensions of the so-called "statistical funnel." The surface expression of this is the area of ocean from which particles originate and that, over the long term, the radius of this surface expression ranged from 90 to 490 km depending on the assumed sinking velocities in the range 20-200 m d −1 .…”