Stanford researchers have identified a surprising and previously unknown connection between deep underwater earthquakes and the growth of massive phytoplankton blooms at the ocean surface. Phytoplankton are microscopic, plant-like organisms that float in sunlit surface waters and form the base of the marine food web. Beyond supporting ocean life, they play a critical role in Earth’s climate system by absorbing carbon dioxide from the atmosphere and producing a substantial share of the planet’s oxygen. The new findings, published in Nature Geoscience, reveal that geological processes far below the seafloor can strongly influence biological productivity at the ocean’s surface.
The study builds on earlier research showing that hydrothermal vents—underwater hot springs found along mid-ocean ridges—release iron-rich fluids that fertilize surface waters, particularly in the Southern Ocean around Antarctica. Iron is a limiting nutrient in this region, meaning phytoplankton growth is constrained by its scarcity. The Stanford team focused on a recurring bloom near the Australian Antarctic Ridge that appeared in the same location and season every year but varied dramatically in size and productivity. In some years, the bloom expanded to cover an area comparable to California; in others, it shrank to the size of Delaware.
After ruling out common environmental drivers such as sea ice extent, temperature, and surface circulation, the researchers turned their attention to the hydrothermal vents beneath the bloom. Lead author Casey Schine proposed a novel idea: that seismic activity might influence how much iron these vents release. Earthquakes are known to alter vent systems by opening clogged pathways, creating new fractures, and increasing heat flow from underlying magma. All of these effects could enhance the discharge of iron-rich fluids into the ocean.
To test this hypothesis, the team analyzed regional earthquake records alongside decades of satellite observations of the bloom. They found a strong correlation: when earthquakes of magnitude 5 or greater occurred in the months preceding the Southern Hemisphere summer—when phytoplankton growth peaks—the resulting phytoplankton blooms were significantly denser and more productive. This provided the first direct evidence linking seismic activity on the ocean floor to biological growth at the surface.
One of the most striking implications of the study is the speed at which hydrothermal iron appears to reach the surface. Traditional thinking suggested that iron from vents would take many years, even decades, to reach surface waters and would disperse far from its source. Instead, the findings imply that iron can rise nearly 6,000 feet within weeks or months and remain close enough to fertilize local blooms. The exact physical mechanisms behind this rapid transport remain uncertain and are now a focus of ongoing research, including a recent expedition to the ridge in late 2024.
Ecologically, the discovery adds a new layer of complexity to the Southern Ocean ecosystem. Phytoplankton blooms support krill and other small organisms that feed larger animals such as penguins, seals, and whales. The study even documented humpback whales feeding near the bloom, highlighting how seismic events could indirectly influence higher levels of the food web. From a climate perspective, understanding what controls these blooms is essential, as phytoplankton blooms play a major role in oceanic carbon uptake. While it remains unclear how widespread this earthquake-driven mechanism is globally, the research opens a new window into how Earth’s interior processes may shape the ocean’s ability to regulate climate.
https://phys.org/news/2025-12-deep-ocean-earthquakes-southern-massive.html