File:Blooms off Western Europe (MODIS 2024-05-12).jpg

English: Brilliant milky-blue swirls marked a spring phytoplankton bloom in the waters of the Celtic Sea in early May 2024. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite acquired this true-color image on May 10.

Phytoplankton are microscopic, plant-like organisms that float near the surface of the ocean year-round. When conditions are favorable—enough daylight, abundant nutrients, and correct water temperature—they can reproduce explosively to create massive blooms that can easily be seen from space.

There are many thousands of species of phytoplankton, each with unique characteristics. While it is usually not possible to determine the species in a bloom from space, one group, the coccolithophores, are identifiable. These tiny organisms surround themselves with hard scales that contain calcite (limestone). A single coccolithophore can be attached to or surrounded by at least 30 of these light-colored scales. When present in large numbers, coccolithophores add a milky tone to the bloom, typically resulting in an opaque turquoise color, such as is seen in this image.