Exercise 2 solution

Sample A: warm (25 degrees), salinity 36. Sample B: cold (5 degrees), salinity 34.

Warmth lowers density and salt raises it. For ordinary seawater the temperature effect from a 20-degree difference is much larger than the effect of a 2-unit difference in salinity. So B (cold, fresher) is denser than A (warm, saltier).

If A is poured gently onto B, A floats on top and the two layers stay separate, forming a stable stratification (a pycnocline between them) until stirring mixes them. Temperature wins here; in polar regions, where all the water is cold, salinity differences matter more.