Layer Formation in Sedimentary Fingering Convection

TL;DR

This paper uses 3D simulations to explore sedimentary fingering convection, revealing layer formation due to sedimentation effects that extend instability regions and introduce new layering mechanisms.

Contribution

It demonstrates the occurrence of layer formation in sedimentary fingering convection through numerical simulations, highlighting effects of sedimentation on instability regions.

Findings

Layer formation occurs in sedimentary fingering convection in certain parameter regimes.

Sedimentation broadens the unstable parameter space for fingering convection.

A new layering instability exists in gamma-stable regimes, though it may grow slowly.

Abstract

When particles settle through a stable temperature or salinity gradient they can drive an instability known as sedimentary fingering convection. This phenomenon is thought to occur beneath sediment-rich river plumes in lakes and oceans, in the context of marine snow where decaying organic materials serve as the suspended particles, or in the atmosphere in the presence of aerosols or volcanic ash. Laboratory experiments of Houk and Green (1973) and Green (1987) have shown sedimentary fingering convection to be similar to the more commonly known thermohaline fingering convection in many ways. Here, we study the phenomenon using 3D direct numerical simulations. We find evidence for layer formation in sedimentary fingering convection in regions of parameter space where it does not occur for non-sedimentary systems. This is due to two complementary effects. Sedimentation affects the turbulent fluxes and broadens the region of parameter space unstable to the $\gamma$-instability (Radko 2003) to include systems at larger density ratios. It also gives rise to a new layering instability that exists in $\gamma-$stable regimes. The former is likely quite ubiquitous in geophysical systems for sufficiently large settling velocities, while the latter probably grows too slowly to be relevant, at least in the context of sediments in water.