What Is a Chlorophyll Edge?

A chlorophyll edge is a sharp boundary between clear, low-nutrient water and green, plankton-rich water: the chlorophyll layer's version of a temperature break, and often the same physical convergence seen from a different measurement.

Why plankton concentration marks an edge

Chlorophyll-a is the pigment phytoplankton use to photosynthesize, so its concentration is a direct proxy for how much plankton is in the water. Two adjacent water masses rarely carry the same plankton load. One is usually nutrient-rich (often from upwelling or river input) and the other comparatively barren. Where they meet, chlorophyll concentration changes sharply, and that seam concentrates the entire food chain built on top of it: plankton, bait, and the predators hunting the bait.

Reading an edge on the fixed log scale

Chlorofishy's chlorophyll layer uses a fixed logarithmic scale from 0.01 to 100 mg/m³ that never adapts to the current view, unlike SST's per-region stretch. That means a real edge always looks the same regardless of which region you're viewing: tightly packed color contours, not a slow fade. See chlorophyll numbers that mean something for what specific values on that scale actually represent.

Not the same thing as runoff-stained water

A high chlorophyll reading doesn't always mean the same thing: plankton-driven productivity and river-runoff turbidity can both register as elevated chlorophyll but represent completely different water. See chlorophyll numbers that mean something for how to tell them apart, and reading water color for what each actually looks like over the rail.

See today's chlorophyll edges on the chlorophyll map. Definition only? Glossary entry. Back to Learn.