Jewels in the Sea Foam

By Henry H. Mitchell, January 2009.
Seafoam at Myrtle Beach

Sea foam washes ashore at Myrtle Beach State Park.

On a dark, overcast, extremely blustery January day in Myrtle Beach, South Carolina, sea foam (see article) was touching the shore, clinging briefly to the sand, then its bubbles popping and disappearing within seconds. However, as we walked along the water's edge, we noticed the appearance of glistening, brightly-colored “jewels” within the ephemeral suds.

For an instant the colors were reminiscent of fiery opals and brilliant emeralds, rubies, and sapphires. But then in a blink the colors subsided to pale aquamarine and were gone. The phenomenon being observed is “thin-film interference” of light, which has a similar effect to diffraction, and is typical of soap bubbles and oil slicks. The light waves reflect from the two surfaces of the film, causing the waves to interact and in the process cancelling out some wavelengths (colors) and intensifying others.

As the filmy, foamy algal-soup-containing suds thin prior to bursting, they become too thin to continue providing the colorful interference effect. Thus the brilliant colors fade almost instantly.

Within a few more minutes, mysteriously, no more of the sea foam we inspected along the beach was producing such a colorful result.

This guide to Myrtle Beach is sponsored by Mitchells Publications.