Double-diffusive convection gradients

Figure 12-6. A sketch of the stability diagram for double-diffusive convection. The stability boundary is the solid line ZXW. The dashed line PQ denotes the boundary for static stability where the net density gradient is equal to zero. It is assumed in this sketch that Pr/Sc < 1.

Figure 9.5 The mechanism of double-diffusive convection in the fingering regime. A/o and Apr are in the opposite direction, and the net density gradient appears to be stable. However, if a small parcel of the warm, salty solution enters the lower section, then because the heat diffuses faster than the salt, the parcel is left with a greater density than the surroimding...

Once again, the stratification is convectively stable until the densities approach equilibration. Then mixing across the liquid-liquid interface is controlled by double diffusive convection, with both temperature and concentration gradients enhancing the density-gradient driven, convective mixing. 

The existence of the Black Sea bottom convective layer (BCL) has important implications for the physical and chemical exchange at the sediment/water interface and at the interface between intermediate and bottom water masses. Two-fold increased vertical gradients of dissolved sulphide at the upper boundary of the BCL suggest the presence of the anoxic interface separating entire anoxic water mass dominated by turbulent diffusion from underlying waters of the BCL where double diffusion is the main mixing mechanism. 

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