Photo Ash erupts high into the atmosphere from Kilauea in 2018. A new study found the eruption sparked a massive phytoplankton bloom that sequestered much of the carbon released during the eruption. Photo courtesy USGS

The 2018 eruption of Kilauea on Hawaii island sparked the largest open-ocean phytoplankton bloom ever recorded in the North Pacific, according to a new international study led in part by scientists at the University of Hawaiʻi at Mānoa.

Published in JGR Oceans, the research links a rare and massive bloom in the nutrient-poor waters of the North Pacific Subtropical Gyre — some 1,200 miles west of the volcano — to the atmospheric fallout of volcanic ash during the May 2018 eruption.

“The scale and duration of this bloom were both massive, and probably the largest ever reported for the North Pacific,” said David Karl, study co-author, Victor and Peggy Brandstrom Pavel Professor and director of the Center for Microbial Oceanography: Research and Education in SOEST.

In a news release, he explained the study shows a connection between the eruption and the bloom formation far from the volcano, and the research can be used to refine scientists’ understanding of phytoplankton bloom dynamics and to improve humans’ understanding of the ocean’s carbon cycle.

While Kilauea has erupted multiple times over the past 40 years, its ash had never before been definitively linked to open-ocean biological impacts.

The 2018 eruption was one of the most significant in two centuries, sending millions of cubic feet of lava into the ocean and releasing tens of thousands of tons of sulfur dioxide and carbon dioxide each day. The ash plume from Kilauea reached nearly five miles into the atmosphere.

Researchers say the ash carried by trade winds fell into nutrient-starved waters, delivering a key ingredient — iron — that helped trigger the bloom. Satellite data confirmed both the movement of ash particles and a visible spike in ocean productivity, as indicated by changes in ocean color.

After an eruption in 2018, ash (top) from Kilauea was deposited where a large open-ocean phytoplankton bloom occurred. Photo courtesy W. Cheah.

“After the 2018 eruption, the prevailing winds transported ash particles to the west,” said Wee Cheah, a corresponding author for the study and senior lecturer in the Institute of Ocean and Earth Sciences at Universiti Malaya.

“The trajectories of the ash were recorded by Earth-orbiting satellites that detect changes in the optical clarity of the atmosphere, the so-called aerosol optical depth,” Cheah continued. “Depending on the density, size, and shape of the particulate matter and local atmospheric conditions, especially rainfall, the ash eventually falls out of the atmosphere and into the surface ocean.”

According to the study’s lead author, Chun Hoe Chow, an associate professor at National Taiwan Ocean University, the team analyzed a combination of satellite data and physical ocean conditions to explain the bloom’s timing and location.

“The waters in the open ocean of the Pacific are nutrient depleted and the addition of volcanic ash — especially iron in the ash — and to a lesser extent other trace elements and possibly phosphate, can stimulate the growth of marine phytoplankton, especially the so-called nitrogen-fixing microbes that can growth in the absence of additional nitrogen,” Karl said.

The bloom not only spurred biological activity but also influenced the ocean’s carbon cycle.

As the phytoplankton died and sank, they exported organic carbon to the deep ocean — potentially offsetting up to half of the carbon dioxide released by the eruption, according to the study.

“This marine carbon dioxide sequestration is a natural process that probably occurs whenever volcanic eruptions inject ash into the atmosphere and carry that particulate matter out to sea,” Karl said.

Researchers say they plan to monitor future eruptions with satellites, and, if possible, deploy a research vessel to study the impact of ash on marine ecosystems in real time.