The foam was back this morning at the lower pools. I'd gone down before the aquarium opened — low...
The foam was back this morning at the lower pools. I'd gone down before the aquarium opened — low...
Low tide this morning, so I walked the reef shelf before opening. The foam was heavy along the...
The thermos cap was off for maybe forty seconds while I poured on the headland this morning, and by...
The foam was still there at noon. I'd come down to check the pools at low tide — the shelf exposed,...
Low tide this morning, cold enough that my breath showed. I spent twenty minutes crouched at the...
Cold enough this morning that my breath sat in the air outside the aquarium for two full seconds. I was eating on the breakwater at low tide when I noticed foam collected in a rock cleft — not the brief bubbles a wave leaves, but a stable, creamy head sitting there for ten or fifteen minutes. The question arrived half-chewed: why does that foam last?
The short answer is surfactants — surface-active molecules dissolved in seawater. Coastal water carries dissolved organic carbon shed by algae and phytoplankton. Some compounds are amphiphilic: one end attracts water, the other repels it. They crowd to the air-water interface and lower local surface tension. When a wave drives air into the water column and bubbles form, surfactant molecules coat the walls and slow collapse. Dish soap works the same way; the ocean does it at lower concentrations with messier chemistry.
The persistence is the interesting part. A clean-water bubble collapses in milliseconds — gravity drains the film until it ruptures. Surfactant-coated films drain more slowly because of the Marangoni effect: any local thinning creates a surface-tension gradient that pulls liquid back into the thinner region, a kind of self-correction. Individual bubbles can last tens of seconds; a foam head sits longer because bubbles support each other mechanically.
The organic load is real. Standard oceanographic references put dissolved organic carbon for this coastal region in the low milligrams-per-litre range — dilute, but enough. The fucoids (brown rockweed) in that cleft shed polysaccharides and lipid fragments continuously. Some fraction will be surfactant-active.
What I don't know: whether foam stability signals anything about algal health, or whether it's just energy input and ambient organic carbon. I've seen claims that unusual foam events can indicate phytoplankton blooms, but separating chemistry from physics from that viewpoint looks genuinely hard.
The foam was still there when I went back inside. Call it a few hundred millilitres — hundreds of millions of stabilised bubbles, each one a small proof of concept.
#science #tidepool #oceanography #notebook