Biosignature seen from space: a phytoplankton bloom

Biosignature seen from space: a phytoplankton bloom

Light green and blue waves spanning hundreds of kilometers brighten the waters of the Celtic Sea in spring 2024 – NASA

editor's Note: Future telescopes may be able to resolve exoplanets in images with multiple pixels. Algal blooms can be huge and possibly grow to a size that one or two pixels in one of these exoplanet images can capture. Is this a potential way to confirm and analyze exoplanet biosignatures?

Light green and blue waves stretching for hundreds of kilometers brightened the waters of the Celtic Sea in spring 2024. Phytoplankton blooms often appear in northern seas as surface waters warm and receive more sunlight in the spring.

Satellites glimpsed the emergence of this colorful region for more than a week before MODIS (Moderate Resolution Imaging Spectroradiometer) on NASA's Aqua satellite acquired this natural-color image on May 10.

Phytoplankton are small, plant-like organisms that often float near the surface of the ocean. With enough carbon dioxide, sunlight, and nutrients, they can grow in huge numbers. In turn, they form the foundation of the aquatic food web, feeding everything from microscopic zooplankton to shellfish to finfish.

The warmth of spring and early summer sets the stage for stunning flower blooms in northern waters such as the Celtic Sea, the North Sea and the Barents Sea. Early in the season, when the water is well mixed and nutrients are abundant, diatom flowers dominate. These phytoplankton, with their silica shells and abundant chlorophyll, give surface waters their green color. As the water warms and stratifies, conditions favor a type of phytoplankton called coccolithophores. Equipped with plates of highly reflective calcium carbonate, they make surface waters appear milky turquoise-blue.

The combination of colors in this flower may be due to a mixture of phytoplankton types. Alternatively, the variety of colors may result from the abundant amount of colored soluble organic matter around the bloom, which can make the seawater appear anywhere from green to yellow-green to brown, depending on the concentration.

Determining which phytoplankton species are present within the bloom has only been possible by analyzing water samples. However, scientists may soon be able to distinguish phytoplankton types from space. The OCI (Ocean Color Instrument) on NASA's PACE (Plankton, Aerosol, Cloud, Ocean Ecosystem) satellite, launching in February 2024, can detect hundreds of wavelengths of light and reveal the species composition of flowers such as these. May be able to.

NASA Earth Observatory image by Michaela Garrison, using MODIS data from NASA EOSDIS LANCE and GIBS/Worldview. Story by Lindsey Dorman.

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