Storms and high winds along coastlines can produce large masses of sea foam. It can form foamy rafts on the water and pile up on beaches, rocky shores, and cliffs. Sea foam often looks like whip cream on an ice cream sundae, a resemblance that is not exactly a coincidence.

Sea foam is typically generated by strong winds, large waves, and the presence of brown seaweed. During storms, the seaweed is battered and macerated releasing a chemical called algin (pronounced AL-jin). When energetic seas whip up algin, it froths up into the foamy marine delight. Differing regions have different types of brown seaweed and the characteristics of the foams vary. Along the west coast of the U.S., much of our sea foam is caused by extensive offshore forests of brown seaweed called giant kelp (Macrosystis pyrifera). Foam made from giant kelp is typically a sign of healthy kelp forests and a healthy ocean.

Algal blooms are another source of organic matter that can produce thick sea foams. If a storm occurs after an algal bloom runs its course, great amounts of decaying matter can be frothed up. Sea foams formed this way can cause really huge and impressive foam events like the one pictured here after an algal bloom by phaeocystis in Northumberland, UK, in 2006. These are natural occurrences but happen when there is some sort of nutrient imbalance−often from upwelling of nutrient-rich waters. Depending on the type of bloom, the foams and their associated aerosols can be irritating to human skin and eyes. These blooms have also resulted in bird deaths when the decaying algae had qualities similar to detergent. The foam can matt down the birds’ feathers, allowing cold seawater to reach their skin. The birds then die from hypothermia.

Formation of sea foam is a bit unpredictable. Not all high winds and surf produce significant sea foam events. Sea foam can even form away from the coast, with no crashing waves. In these cases it apparently takes winds blowing fast enough to break the surface tension of water: about 6 meters per second.

Algin from brown seaweed is edible. It has significant commercial use in thousands of products as a thickening, stabilizing, or emulsifying agent. You will find it in many products like cosmetics, paint, ice cream and prepared whipped products! It’s entirely likely you eat some product made of seaweed on a regular basis. Ice cream sundae any body? Pudding?

Brown seaweeds cannot typically be cultivated. They need to go through a reproductive cycle involving an alternation of generations. This makes it more expensive than harvesting and transporting wild seaweeds. As such, seaweed is harvested from the ocean in many coastal areas around the world.

The idea and much of the research and writing of this article was done by Bay Net volunteer Patrick Wilkinson. Thank you Patrick!

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