Phytoplankton in the upper ocean are food for fish and are thus economically important to humans; furthermore, phytoplankton consume nutrients and generate oxygen by photosynthesis, just like plants on land. Vertical mixing in the ocean is responsible for transporting nutrients into the sunlit zone of the surface ocean. We used remotely sensed data to quantify the influence of tidal mixing on phytoplankton through an analysis of ocean color, which we interpret as chlorophyll concentration.