By Emily Cassidy
NASA Earth Observatory– From global to regional scales, satellite images depict the dynamic beauty of the world’s oceans. Each view reveals something unique, from the seasonal pulses of life to the colorful signature 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 like the Earth’s lungs and produce about half of the oxygen we breathe.
One way scientists can track phytoplankton in the ocean is by measuring concentrations of chlorophyll, the compound that allows phytoplankton and plants to absorb energy from the sun. There are several kinds of chlorophyll, but they absorb all blue and red wavelengths of the electromagnetic spectrum and reflect green light.
The animation above, comprised of a series of images acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite, shows chlorophyll concentrations in the planet’s oceans from January 2021 through January 2022. The light yellow areas on the maps show where chlorophyll concentrations are high; darker blue areas indicate where they are low.
As the seasons change, chlorophyll concentrations change with them. Chlorophyll is especially abundant in spring and early summer, when light and abundant nutrients promote huge blooms of phytoplankton.
“Ocean color provides us with important information about phytoplankton, ocean health, and global climate,” said Ivona Cetini?, 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 seafloor shape (bathymetry), ocean currents, and nutrient availability. Near the coasts, phytoplankton feed on the abundant nutrients washed into the ocean from land and the upwelling of cold, nutrient-rich water from the deep ocean. In many cases, the flowers 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.
Some of the highest chlorophyll concentrations are found in cold polar waters, where nutrients accumulate during the dark winter months. When the spring sun returns, phytoplankton flourish. Near the equator, a series of high concentrations of chlorophyll can be observed where warm upper ocean waters mix with cooler, nutrient-rich waters from the depths. This process, known as equatorial upwelling, creates ideal conditions for phytoplankton to thrive throughout the year.
High levels of chlorophyll also appear at mid-latitudes. On the global map, notice the seasonal abundance of chlorophyll off the coast of Argentina. This area, known as the “shelf-break front”, is at the crossroads of ocean currents. The nutrients they carry often produce dazzling displays of phytoplankton in the spring and summer.
These flowers are especially eye-catching in natural color satellite images. 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 Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite. Turbulent conditions on the edge of the continental shelf generated swirls of water traced by phytoplankton that painted the water blue and green.
“The color of the swirls can tell us something about the type of plankton present in the bloom,” Cetini said? said. She noted that it is difficult to immediately tell the types of phytoplankton present. Understanding the different types of phytoplankton found in the ocean can tell us about the cycling of not only carbon but also other nutrients.
Although the colors of the phytoplankton bloom off Patagonia are impressive, NASA’s existing satellite fleet has some limitations in understanding ocean ecology. Some of those limitations may soon be resolved, according to Cetini?, the ocean biogeochemistry science lead for an upcoming NASA satellite called the Plankton, Aerosol, Cloud, Ocean Ecosystem (PACE) mission.
“PACE is hyperspectral, which means it will be able to see many different hues and will help us distinguish the types of phytoplankton present. It will also help us quickly identify and predict harmful algal blooms,” Cetini said. said. Switching to PACE to understand ocean ecology “will be like switching from a flip phone to the latest smartphone.”
NASA Earth Observatory images and video by Joshua Stevens, using NASA Ocean Color Web data and VIIRS data from NASA EOSDIS LANCE, GIBS/Worldview and the Suomi National Polar-orbiting Partnership. Emily Cassidy Story.
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