Shear-Generating Roller Tanks for Studying Marine Snow Disaggregation

Particulate matter plays a key role in the export of material from the surface ocean through its sedimentation. However, the complexity of particle dynamics in the ocean, which includes variable particle content (organics and inorganics), aggregate size, shape, and fractal dimension and density, still limits our ability to accurately understand and model marine particle transport. In particular, physical disaggregation of marine particles is poorly understood and has not yet been adequately represented in biogeochemical transport models. Roller tanks with solid body rotation are typically used in the laboratory for studying dynamics of marine snow, especially artificial aggregation. However, due to the lack of shear forces, neither fragmentation nor shear-induced aggregation can be investigated with these traditional tanks. Here, we implement a new roller tank design where a periodic oscillation is superimposed onto a constant tank rotation. The laminar oscillating flow exposes particles to calibrated time-varying fluid shear forces. Under certain operating conditions, particles near the edge of the tank experience shear similar in magnitude to that in the surface ocean. As the tank rotates and oscillates, the position history of each aggregate is tracked with a high-speed camera until the point of disaggregation. We present the fragmentation characteristics of two types of marine aggregates, including marine snow aggregates of diatoms and inorganic clay flocs, and discuss their relation to disaggregation models for biogeochemical export predictions.