In January this year, the largest underwater volcanic eruption of the century triggered a spectacular bloom of phytoplankton north of Tongatapu in the Kingdom of Tonga. A study led by researchers from the University of Hawaii at Manoa and Oregon State University found that microscopic marine life covered an area about 40 times the size of Gran Canaria, roughly equivalent to the entire Valencian Community, just 48 hours after the eruption.
Driving the research, the UH Manoa School of Ocean and Earth Science and Technology (SOEST) team analyzed satellite imagery and concluded that volcanic ash deposition likely served as the key nutrient source fueling this unprecedented phytoplankton surge.
Phytoplankton consists of tiny photosynthetic organisms that generate oxygen and form the base of the marine food web. Their growth is typically limited by available nutrients at the ocean surface, but sudden nutrient inputs can unleash rapid, widespread blooms.
“Although the Hunga Tonga-Hunga Ha’apai eruption occurred underwater, it released a large ash cloud that reached tens of kilometers into the atmosphere,” noted a scientist from the Center for Microbial Oceanography (C-MORE) at SOEST. “The ash fallout provided nutrients that stimulated phytoplankton growth and reached concentrations well above regional norms.”
“We were impressed to observe such a vast area showing high chlorophyll levels in a short time after the eruption,” added Dave Karl, co-author and director of C-MORE. “This demonstrates how quickly the ecosystem can respond to nutrient fertilization.”
“An observer can see very different parts of this environment—an eruption that caused a major ecological shift in nearby oceans,” remarked Ken Rubin, a volcano specialist at SOEST and study author. “Our findings reveal the extensive interdependence of volcanic activity and shallow marine ecosystems, highlighting a global link between volcanism and coastal biology.”
Lessons from Kilauea
Three of the researchers had previously examined a smaller phytoplankton bloom associated with the 2018 Kilauea eruption, a discovery that already pointed to the potential consequences of volcanic activity for ocean ecosystems.
“When the Tonga eruption occurred, it was straightforward to adapt the satellite-analysis program I had built for Hawaii to assess the impact on the neighboring ocean,” said Barone. “From the first look at the results, it was clear there was a rapid phytoplankton response over a wide area.”
Phytoplankton remove carbon dioxide from the atmosphere, making them critical players in the global climate system. The eruption acted as a natural fertilization event, demonstrating how quickly these microscopic engines can respond when nutrients are in place.
“The dynamics of this event help predict how pelagic environments will behave when nutrients enter otherwise nutrient-poor regions of the ocean,” Barone noted. “This information can inform discussions about ocean fertilization as a strategy for carbon removal.”
Reference work: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2022GL099293
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