In 2018, Kīlauea volcano in Hawai‘i sent a towering plume of ash nearly five miles into the sky – and it travelled far and wide.
In fact, scientists now believe that this ash kickstarted an even mightier event over 1,200 miles away in the North Pacific Ocean.
The international team of researchers recently published their findings in JGR Oceans, revealing that the falling volcanic ash helped trigger one of the largest phytoplankton blooms ever recorded in the North Pacific Subtropical Gyre.
"The scale and duration of this bloom were both massive, and probably the largest ever reported for the North Pacific,” says Professor David Karl from the University of Hawai‘i at Mānoa, explaining that the event shows how an eruption on land can affect ocean life far out to sea.
"This can be used to refine our understanding of phytoplankton bloom dynamics and to improve our understanding of the ocean's carbon cycle.”
Earth, air and sea
Phytoplankton are tiny, plant-like organisms that form the base of the marine food web. But they also play a key role in capturing carbon dioxide from the atmosphere. While Kīlauea is one of the world’s most active volcanoes, this is the first time ash from one of its eruptions has been linked to a bloom so far offshore.
The 2018 eruption was the volcano’s biggest in over two centuries. Rivers of lava poured into the sea, releasing huge amounts of gases – around 50 kilotons of sulphur dioxide and 77 kilotons of carbon dioxide every day at its peak.
Earlier studies had already shown that when hot lava enters the ocean, it heats nutrient-rich water from the deep and lifts it to the surface. Sunlight then helps phytoplankton thrive. But volcanic ash, blown sky-high and carried on the wind, can travel even further – and in this case, that’s exactly what happened.
After the eruption, ash particles were swept westward by strong winds, explains co-author of the study Dr Wee Cheah from Universiti Malaya. The researchers used satellite data to track where the ash went, and how much of it eventually settled into the sea.
Alongside that, the team analysed changes in ocean colour – a way of detecting phytoplankton from space. What they found was striking: a vast bloom near the dateline, in an area where blooms like this are rare.
The ash, it turns out, carried valuable nutrients – especially iron, which phytoplankton need to grow. These nutrients are normally scarce in the open Pacific, so when they suddenly appeared, the phytoplankton responded.
Marine carbon sink
The bloom created a huge amount of organic matter. When the phytoplankton died, much of that matter sank to the ocean floor, taking carbon with it – a natural form of carbon capture.
“Our estimates are that export of organic carbon may be equivalent to about half of the carbon dioxide initially released from the eruption,” says Karl.
"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.
"The combination of ash deposition and the nutrient starved conditions in our study area aligned to create a massive bloom that was easily seen by satellite remote sensing and Argo floats that had been previously deployed in that region.”
Looking ahead, the researchers hope to monitor future volcanic eruptions and their effects in real time. If another major event occurs, they plan to send out a research vessel to observe how the bloom unfolds.
Find out more about the study: Kı̄lauea Volcanic Ash Induced a Massive Phytoplankton Bloom in the Nutrient-Poor North Pacific Subtropical Gyre
Main image: Kīlauea volcanic eruption in 2018. Credit: Getty
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