I noted an interesting phenomenon at Weymouth in Dorset recently. The rusty iron panels of the pier structure exhibited tide-marks or tide-lines of dried sea foam from a previous high water. I have never seen that before. The contrasting colours, patterns, and textures of the creamy lines against the multi-coloured oxidising metal made interesting compositions.
Wikipedia says about sea foam:
Sea foam, ocean foam, beach foam, or spume is a type of foam created by the agitation of seawater, particularly when it contains higher concentrations of dissolved organic matter (including proteins, lignins, and lipids) derived from sources such as the offshore breakdown of algal blooms. These compounds can act as surfactants or foaming agents. As the seawater is churned by breaking waves in the surf zone adjacent to the shore, the presence of these surfactants under these turbulent conditions traps air, forming persistent bubbles that stick to each other through surface tension. Due to its low density and persistence, foam can be blown by strong on-shore winds from the beachface inland.