For centuries, sailors have described vast oceanic areas emitting an eerie glow, as if bathed in non-existent moonlight. These "milky seas," as rare as they are enigmatic, may finally be understood thanks to a recent study.
Researchers from Colorado State University have compiled the first comprehensive database on these phenomena, cross-referencing historical accounts with satellite observations. Their work, published in
Earth and Space Science, reveals unexpected patterns linked to climate cycles.
Light from the depths
The bioluminescence of milky seas would originate from bacteria, particularly Vibrio harveyi. Unlike the flashes of microalgae, their light is continuous, comparable to an artificial starry sky.
These events sometimes cover areas larger than entire countries, as evidenced by satellite images. Their duration can exceed a month, according to reports from ships crossing these ghostly zones.
Accounts often describe an abnormally calm sea, almost frozen. Analyses suggest that substances emitted by phytoplankton could calm the waves, amplifying the spectral effect.
Climate and oceanic mysteries
The database lists fewer than 400 confirmed occurrences since the 17th century, mostly in the northwestern Indian Ocean.
Researchers have identified correlations with phenomena such as La Niña or the Indian Ocean Dipole. Monsoons, by bringing up nutrients from the depths, would favor this bacterial proliferation.
Some questions remain: does this phenomenon signal a threat to ecosystems? Vibrio harveyi being pathogenic to fish.
Article author: Cédric DEPOND