The Strange Link Between Winter Earthquakes and Massive Summer Algae Blooms The Size of California

A satellite view of a phytoplankton bloom in the Southern Ocean. Credit: NASA During the Antarctic winter, sea ice spreads and sunlight fades, leaving little visible change at the ocean surface. Deep below, however, earthquakes shake underwater ridges and stir mineral-rich fluids from the seafloor. New research suggests this wintertime activity helps shape how much marine life flourishes months later, when summer returns. A study published in Nature Geoscience links wintertime earthquakes in the Southern Ocean to the growth of massive phytoplankton blooms in summer. The finding connects geology, biology, and climate in a way scientists had not documented before-and suggests the ocean’s ability to absorb carbon dioxide may depend partly on the planet’s shifting crust. Phytoplankton are microscopic organisms that float near the ocean surface. They form the base of the marine food web and pull carbon dioxide from the air as they grow. In the Southern Ocean, their growth is constrained not by sunlight or nitrogen, but by iron-a trace nutrient in short supply. The Earthquake-Plankton Connection Researchers have consistently tracked a recurring bloom near Antarctica that reliably appears each summer, yet varies dramatically in size. In some years, the bloom spreads across a vast stretch of ocean. In others, it contracts sharply, covering only a small fraction of that area. The new findings offer an unexpected explanation. That variability turns out to trace back to a specific stretch of seafloor. The work focuses on the Australian Antarctic Ridge, a volcanically active chain of underwater mountains where tectonic plates grind past one another. Hydrothermal vents dot the ridge, releasing hot, iron-rich fluids into the surrounding water. Earlier studies had shown that iron from these vents can reach the surface and fertilize phytoplankton. What remained unclear was why the bloom’s productivity rose and fell so sharply from year to year. “When looking back over satellite observations of this bloom, we’ve seen it swell to the size of the state of California or down to the size of Delaware,” said Casey Schine, the study’s lead author, in a Stanford University statement. × Get smarter every day... Stay ahead with ZME Science and subscribe. Thank you! One more thing... Please check your inbox and confirm your subscription. “Our study ultimately showed that the main factor controlling the size of this annual phytoplankton bloom was the amount of seismic activity in the preceding few months.” Schine and her colleagues compared more than 20 years of satellite measurements of phytoplankton growth with detailed records of underwater earthquakes. A clear pattern emerged. When earthquakes of magnitude 5 or greater on the moment magnitude scale struck the ridge during the Antarctic winter, the following summer’s bloom was denser and more productive. The link likely runs through hydrothermal vents. Earthquakes can alter their internal plumbing, opening new cracks or clearing blockages. The result is a surge of iron-rich fluid entering the ocean-just in time to influence the next growing season. Unexpectedly Fast Dispersion Deployment of an instrument used to collect water samples from different ocean depths...

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