A warm salty parcel can change its mind

Start with a small parcel from a warmer, saltier upper layer. Compare it with colder, fresher water below. Then let the parcel lose heat while retaining its salt.

Default: initially 0.43 kg/m³ lighter; after heat exchange 0.18 kg/m³ denser than the reference lower water.
What the calculation does—and leaves out

We use a linear density approximation Δρ = 1025[−0.0002ΔT +0.00076ΔS], in kg/m³. Heat loss reduces ΔT while ΔS stays fixed. These illustrative coefficients are held constant; real seawater properties vary with temperature, salinity and pressure.

This is a thought experiment about buoyancy. It is not a numerical salt-finger simulation and calculates no growth rate or ocean mixing flux. Salt also diffuses in reality. Whether fingers develop depends on gradients, diffusion, geometry and competing motions.

Try setting the heat-loss slider to zero, then increase it slowly. A change from lighter to denser illustrates why unequal rates of heat and salt exchange matter. If the parcel is already denser before heat exchange, the example has ordinary overturning instability rather than the initially stable arrangement discussed in the article.

Background: WHOI’s tracer experiment. Values are illustrative; this page sends no information.