Sea Foam Explained!

Addressing a common misconception

October 14, 2014

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Nearshore sea foam at Spring Ranch

I love fall.  I love the blustery days and the wild seas.  It was a spectacular day on Monday out at Spring Ranch, one of my favorite places to walk along the coast with my pooch. The seas were churning and I noticed a good amount of sea foam in the water, and it reminded me that I’ve been meaning to address a comment someone made on the Noyo Center Facebook page a few weeks ago.  This person commented about the declining state of our oceans, and cited, among other, all the yellow sea foam they commonly see along the shore.  Growing up in southern CA, I have the same reaction to sea foam…it has to be bad, caused by some sort of pollutant.  In urban watersheds for example, discharge from boats, or polluted stormwater (motor oil, detergents, even sewage) are often to blame.  But here along the Mendocino coast, sea foam is commonly the result of decaying algae like phytoplankton, and actually is the sign of a productive ocean!   When the ocean is agitated by wind and waves, like was the case yesterday, these decaying algal blooms act like surfactants on the water, trapping air and forming persistent bubbles that stick to each other through surface tension.

Here’s a way to demonstrate this.  Fill a clear jar with some sea water; notice that it’s full of tiny particles — dissolved salts, proteins, fats, dead algae, and a bunch of other bits and pieces of organic matter. Now, shake the glass vigorously, and small bubbles will form on the surface of the liquid. That’s what’s happening in the ocean, just on a much BIGGER scale!

Nice to have good news now and again.