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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...
Cold enough this morning that my breath sat in the air outside the aquarium for two full seconds. I...
Low tide this morning, cold enough that my breath showed. I spent twenty minutes crouched at the...
The foam was still there at noon. I'd come down to check the pools at low tide — the shelf exposed, kelp draped flat — and one pool had a thick raft of white foam wedged into its northern corner. Four hours later, walking back, it was barely diminished. That seemed worth sitting with.
The question: why does foam in a tide pool outlast foam on an open wave face?
Foam is air bubbles stabilised by a thin water film. In pure water, that film drains in seconds — surface tension pulls liquid to the bubble borders until the film ruptures. What keeps foam alive is surfactant: surface-active molecules that park at the air-water interface and slow drainage. In the ocean, these come mostly from biological sources — algal exudates, mucus, degraded cell-membrane material.
Tide pools are, per litre, richer in dissolved organic matter than the open ocean surface. More surfactant, more stable foam. The pool I was looking at was dark and faintly iridescent, which I take as a rough proxy for high organic load. I don't have a number for the relationship, but the direction is clear.
The second factor is confinement. On a wave face, mechanical disruption is continuous — new water arrives, jets of spray shatter the structure. In a sheltered corner, the foam sits undisturbed. The characteristic drainage time for a well-stabilised foam under calm conditions is probably tens of minutes to an hour, consistent with what I observed.
What I'm less certain about: temperature. The pool had warmed from around 14°C to maybe 18°C through the morning. Lower surface tension at higher temperature should accelerate drainage, but lower viscosity might counteract that in some geometries. I genuinely don't know the sign of the net effect without working through the fluid dynamics properly, and I haven't done that yet.
Confident conclusion: organically rich water, plus mechanical shelter. The temperature question stays open.
#science #tidepool #foam #notebook
