“Exploring the Hidden Life: Phytoplankton and Biosignatures in the Patagonian Ocean”

Editor’s remark: upon our initial missions – whether human or robotic – reaching a new celestial body, we will aim to extract as much data as possible from space – through flybys or orbiting – before contemplating landing. If fortune favors us, telescopic observations will precede this stage – observations that may have spotted biosignatures and designated a world deserving of further investigation. The means by which we accomplish this will hinge on the tools at our disposal. Fortunately, astrobiology mission strategists possess a knowledge base built over half a century of Earth and planetary observation spacecraft. Understanding our own living planet serves as an ideal foundation for planning future extraterrestrial missions focused on detecting and characterizing life on the surface below.

Communities of these minuscule aquatic organisms sustained themselves throughout the extended days of summer in the Southern Hemisphere, coloring surface waters in hues of green and blue up until late December.

The Ocean Color Instrument (OCI) aboard NASA’s PACE (Plankton, Aerosol, Cloud, ocean Ecosystem) satellite obtained this view of the bloom and its detailed patterns around the Falkland Islands (Islas Malvinas) on December 28, 2024.

In the waters at the Patagonian Shelf-break front, airborne dust from the mainland, iron-enriched currents, and upwelling from the ocean depths deliver plentiful nutrients essential for phytoplankton. These floating solar collectors support diverse aquatic life and thriving fisheries.

The array of colors visible in the image hints at a variety of phytoplankton communities. The composition of these communities shifts throughout the duration of the bloom, influenced by nutrient supply and other environmental conditions. In this instance, chlorophyll-abundant diatoms and other phytoplankton species that tint the water green may be transitioning to coccolithophores, noted Ivona Cetinić, an oceanographer at Morgan State University and part of NASA’s Ocean Ecology lab.

“Coccolithophores thrive in long days with abundant sunshine, indicating they are likely predominant now,” she stated. Encased within plates of highly reflective calcium carbonate, these organisms render surface waters a milky turquoise-blue. The coccolithophore bloom that takes place annually off Patagonia forms part of the Great Calcite Belt, which is believed to significantly influence the Earth’s carbon cycle.

The variation in colors within the image also unveils intricacies of the ocean’s surface waters. “Plankton cannot navigate against currents,” remarked Cetinić, “thus the various color stripes represent distinct water masses possessing different concentrations of elements necessary for the growth of various phytoplankton types.”

Identifying the specific phytoplankton types present in a bloom using only remote sensing imagery remains a persistent challenge. Nevertheless, researchers are making strides aided by the hyperspectral (fine wavelength resolution) data collected by the PACE satellite. Cetinić and her team have developed a tool that allows them to differentiate amongst three distinct phytoplankton communities based on hyperspectral signatures.

While the researchers view the method as promising, they acknowledge that it is still in its developmental stages. Observing phytoplankton on a global scale through daily data from PACE could assist scientists and resource managers in assessing fisheries health, monitoring harmful algal blooms, and identifying shifts in the marine ecosystem.

NASA Earth Observatory image by Wanmei Liang, utilizing PACE data from NASA EOSDIS LANCE and GIBS/Worldview. Article by Lindsey Doermann.

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Astrobiology