This global map shows chlorophyll concentrations between January 2021 and January 2022
This global map shows chlorophyll concentrations between January 2021 and January 2022

From global to regional scales, satellite images represent the dynamic beauty of the world’s oceans. Each view reveals something unique, from the seasonal pulses of life to the colorful imprint of phytoplankton blooms.

Almost all life in the ocean depends on tiny photosynthetic organisms known as phytoplankton. These microscopic plant-like organisms capture carbon dioxide from the atmosphere and release oxygen. Phytoplankton act as the lungs of the Earth and have produced about half of the oxygen we breathe.

One way scientists can monitor phytoplankton in the ocean is by measuring concentrations of chlorophyll, the compound that allows phytoplankton and plants to absorb energy from sunlight. There are several types of chlorophyll, but they all absorb the blue and red wavelengths of the electromagnetic spectrum and reflect green light.

The above animation, made up of a series of images acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA’s Aqua satellite, shows chlorophyll concentrations in the planet’s oceans since January 2021 through January 2022. Light yellow areas on the maps show where there are high concentrations of chlorophyll; darker blue areas show where they are scarce.

As the seasons change, chlorophyll concentrations change with them. Chlorophyll is especially abundant in the spring and early summer, when abundant light and nutrients support huge phytoplankton blooms.

“The color of the ocean gives us important information about phytoplankton, ocean health and global climate,” said Ivona Cetinić, an oceanographer at Morgan State University and a member of NASA’s Ocean Ecology Laboratory.

Regional differences in chlorophyll concentrations are due to factors such as the shape of the seafloor (bathymetry), ocean currents, and nutrient availability. Near the coasts, phytoplankton grow thanks to the abundant nutrients that are washed into the ocean from the ground and the upwelling of cold, nutrient-rich waters from the ocean depths. In many cases, these phytoplankton blooms are harmless. But the rapid growth of certain types of phytoplankton in shallow coastal waters can create harmful algal blooms, which can kill fish and produce toxins harmful to human health.

This global map shows chlorophyll concentrations between January 2021 and January 2022
November 21, 2022

Some of the highest concentrations of chlorophyll can be found in cold polar waters, where nutrients accumulate during the dark winter months. When the spring sunlight returns, phytoplankton proliferate. Near the equator, a patch of high chlorophyll concentrations can be seen where warm surface ocean waters mix with cooler, nutrient-rich deep waters. This process, known as equatorial upwelling, creates the ideal conditions for phytoplankton to thrive throughout the year.

High levels of chlorophyll also appear in the mid-latitudes. On the global map, the seasonal abundance of chlorophyll is observed off the coast of Argentina. This area, known as the “shelf rupture front,” is at a crossroads of ocean currents. Nutrients carried by these waters often produce dazzling displays of phytoplankton in the spring and summer.

These blooms are especially striking in natural color satellite imagery. As summer approached in the southern hemisphere, a phytoplankton bloom became visible off the coast of Argentina. This image was acquired on November 21, 2022 with the MODIS instrument aboard NASA’s Terra satellite. Turbulent conditions at the edge of the continental shelf generated eddies of water traced by phytoplankton that dyed the water blue and green.

“The color of the eddies can give us information about the type of plankton present in the bloom,” Cetinić said.

He noted that it’s hard to know right away what types of phytoplankton are present. Understanding the different types of phytoplankton found in the ocean can provide information not only about carbon cycling, but about other nutrients as well.

Although the colors of the phytoplankton bloom off Patagonia are impressive, NASA’s existing fleet of satellites has some limitations in understanding ocean ecology. Some of these limitations could be resolved soon, according to Cetinić, head of the ocean biogeochemistry science team for an upcoming NASA satellite called Plankton, Aerosol, Cloud, Ocean Ecosystem (PACE).

“PACE is hyperspectral, which means it will be able to see many different hues and will help us differentiate what types of phytoplankton are present. It will also help us quickly identify and forecast harmful algal blooms,” Cetinić said.

Moving to using PACE to understand ocean ecology, “will be like moving from a foldable mobile phone to the latest smartphone.”