Chlorophyll-a

The green pigment in phytoplankton. Its concentration at the ocean surface is the standard proxy for how much plant life — the base of the marine food web — is present.

Why it matters

Ocean-color sensors read chlorophyll to track blooms, fisheries productivity, and how the ocean’s biology responds to a changing climate.

In plain terms

The ocean’s “greenness.” More chlorophyll = more microscopic plants = a busier, more productive patch of sea.