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Comment on gmd-2021-195

2021

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This is a peer-review comment on a study presenting parameterisations for wind-driven turbulent mixing in ocean surface mixed layers for use in Lagrangian particle tracking models. The comment engages with the methodology for modelling vertical transport of particles — including microplastics — in the ocean.

Study Type Environmental

Abstract. Turbulent mixing is a vital component of vertical particulate transport, but ocean global circulation models (OGCMs) generally have low-resolution representations of near-surface mixing. Furthermore, turbulence data are often not provided in OGCM model output. We present 1D parametrizations of wind-driven turbulent mixing in the ocean surface mixed layer that are designed to be easily included in 3D Lagrangian model experiments. Stochastic transport is computed by Markov-0 or Markov-1 models, and we discuss the advantages and disadvantages of two vertical profiles for the vertical diffusion coefficient Kz. All vertical diffusion profiles and stochastic transport models lead to stable concentration profiles for buoyant particles, which for particles with rise velocities of 0.03 and 0.003 m s−1 agree relatively well with concentration profiles from field measurements of microplastics when Langmuir-circulation-driven turbulence is accounted for. Markov-0 models provide good model performance for integration time steps of Δt≈30 s and can be readily applied when studying the behavior of buoyant particulates in the ocean. Markov-1 models do not consistently improve model performance relative to Markov-0 models and require an additional parameter that is poorly constrained.

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Comment on gmd-2021-195

AI summary Read the abstract

This is a reviewer comment on a modeling study about turbulent mixing and vertical transport of particles in ocean circulation models, with no original research content.

Article Tier 2

Comment on gmd-2021-195

AI summary Read the abstract

This is a reviewer comment on a modeling study about turbulent mixing and vertical particle transport in ocean circulation models, with no original research content.

Article Tier 2

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AI summary Read the abstract

This study found that current models tend to overestimate how quickly wind and waves mix floating microplastics down into the water, because they don't fully account for how buoyancy slows particles' vertical movement in turbulent water. This matters because more accurate models help scientists better predict where microplastics actually concentrate in the ocean, key information for understanding where marine life (and eventually, our seafood) encounters the most contamination.

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