Chlorophyll Front

A chlorophyll front is a sharp horizontal gradient in surface chlorophyll-a concentration, the optical signature of a boundary between water masses of different productivity. Fronts form where physical convergence, upwelling, or shelf-break dynamics separate nutrient-rich, high-chlorophyll water from oligotrophic water, often aligned with a thermal or salinity front. Ocean-color sensors such as MODIS and Sentinel-3 OLCI map these fronts at roughly 300 m to 1 km resolution and gradient-detection algorithms track them in time. Chlorophyll fronts aggregate plankton and fish, mark feeding grounds for higher predators, and guide fishing and survey effort.