Fig. 5: Tracer spreading in shallow and steep-sided basins.

A schematic depicting the spreading of tracer in (a) a shallow-sided basin and (b) a steep-sided basin. Note that while w is constant and negative (i.e., upward) in both basins, the apparent advection velocity of the tracer peak W = w + κv/L can be positive (i.e., downward) when L is small and diffusivity κv is large.