By Lina carolina 
The colossal eruption of Hawaiʻi’s Kīlauea Volcano in May 2018, which spewed an immense plume of ash nearly five miles into the atmosphere, has been directly linked to an extraordinary and rare summertime phytoplankton bloom in the North Pacific Subtropical Gyre. This unprecedented event, documented by an international team of researchers, occurred approximately 1,200 miles west of the volcano and highlights a profound, previously underappreciated connection between terrestrial volcanic activity and oceanic productivity. The groundbreaking findings of this study were recently published in the esteemed scientific journal JGR Oceans.
This research unveils a significant, far-reaching consequence of Kīlauea’s powerful eruption, demonstrating how volcanic materials, transported vast distances by atmospheric currents, can dramatically influence marine ecosystems. The scale and duration of the North Pacific bloom were described as "massive," potentially the largest ever recorded for that region, according to David Karl, a co-author of the study and the Victor and Peggy Brandstrom Pavel Professor and Director of the Center for Microbial Oceanography: Research and Education at the University of Hawaiʻi (UH) at Mānoa School of Ocean and Earth Science and Technology. "Our study shows the connection between the eruption of Kīlauea and bloom formation far from the volcano," Karl stated. "This can be used to refine our understanding of phytoplankton bloom dynamics and to improve our understanding of the ocean’s carbon cycle."
The Kīlauea Eruption: A Scale of Unprecedented Proportions
Kīlauea, a volcano renowned for its frequent activity and recognized as one of the world’s most active, has experienced multiple eruptions over the past four decades. However, the 2018 event stood out due to its sheer magnitude. It was one of the largest eruptions in over 200 years, characterized by the dramatic injection of millions of cubic feet of molten lava into the ocean off the Big Island of Hawaiʻi. The atmospheric impact was equally staggering, with an estimated daily release of 50 kilotons of sulfur dioxide and approximately 77 kilotons of carbon dioxide into the atmosphere.
While volcanic activity on Hawaiʻi Island has historically influenced local marine environments, the direct linkage of Kīlauea’s ash to widespread open-ocean phytoplankton blooms was not previously established. Previous research, spearheaded by UH Mānoa oceanographers, had identified localized phytoplankton stimulation near the Big Island. This occurred as lava flowed into the ocean, warming nutrient-rich bottom waters and causing them to become more buoyant. This upwelling of nutrient-laden deep water to the sunlit surface provided the necessary sustenance for phytoplankton growth, leading to visible microbial blooms offshore of Hawaiʻi Island. However, the 2018 eruption’s explosive nature propelled ash to much higher altitudes, facilitating its long-distance transport by prevailing winds.
Tracing the Ash: From Volcano to Ocean
The journey of Kīlauea’s ash across the Pacific was meticulously tracked by the research team. "After the 2018 eruption, the prevailing winds transported ash particles to the west," explained Wee Cheah, the study’s corresponding author and Senior Lecturer at the Institute of Ocean and Earth Sciences at Universiti Malaya. Satellite data played a crucial role in this tracking process. Earth-orbiting satellites equipped to detect changes in atmospheric optical clarity, often referred to as aerosol optical depth, provided crucial evidence of the ash plume’s trajectory. The dispersal and eventual fallout of these ash particles into the surface ocean were contingent upon various factors, including the density, size, and shape of the particulate matter, as well as prevailing atmospheric conditions, particularly rainfall, which can accelerate deposition.
The study’s lead author, Chun Hoe Chow, an Associate Professor in the Department of Marine Environmental Informatics at the National Taiwan Ocean University, and his co-authors utilized a multi-pronged approach. Beyond tracking the atmospheric transport of ash, they analyzed satellite imagery of ocean color. This remote sensing technique provides an indirect but reliable measure of phytoplankton abundance; a greener hue in the ocean typically indicates a higher concentration of these microscopic marine plants. The satellite data revealed a substantial bloom in the vicinity of the International Date Line, a region not typically known for such widespread seasonal productivity.
The Chemistry of Bloom: Iron and Other Nutrients
The significant phytoplankton bloom observed in the North Pacific Subtropical Gyre was a direct consequence of the nutrient enrichment provided by the Kīlauea ash. "The waters in the open ocean of the Pacific are nutrient depleted," Professor Karl elaborated. "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."
Iron is a particularly vital micronutrient for phytoplankton, playing a key role in photosynthesis and nitrogen assimilation. In many oceanic regions, iron availability is a limiting factor for primary production. Volcanic ash is a rich source of iron and other essential trace metals. The study suggests that these volcanic inputs acted as a powerful fertilizer for the phytoplankton in the otherwise nutrient-poor waters of the gyre. Furthermore, the ash likely contained other beneficial elements, such as phosphate, which further contributed to the explosive growth. The research also pointed to the stimulation of "nitrogen-fixing microbes," a specialized group of phytoplankton capable of converting atmospheric nitrogen into a usable form, enabling them to thrive even in the absence of additional nitrogen in the water column.
Chronology of Events
- May 2018: Kīlauea Volcano erupts, releasing an immense ash plume into the atmosphere.
- May – Summer 2018: Prevailing winds transport volcanic ash westward across the Pacific Ocean.
- Summer 2018: Ash particles fall onto the surface of the North Pacific Subtropical Gyre, approximately 1,200 miles west of Hawaiʻi.
- Summer 2018: Nutrient enrichment from volcanic ash stimulates a massive phytoplankton bloom in the gyre.
- Post-Summer 2018: Phytoplankton die and sink, exporting organic carbon to the deep ocean.
- Recent Publication: International research team publishes findings in JGR Oceans, linking the eruption to the bloom and its carbon sequestration potential.
Carbon Sequestration: A Natural Climate Regulator
The implications of this massive phytoplankton bloom extend beyond mere ecological observation; they touch upon the crucial issue of the ocean’s role in regulating Earth’s climate. The exponential growth of phytoplankton during the bloom produced a substantial amount of organic matter. When these microscopic organisms complete their life cycle, they die and sink to the deep ocean. This process, known as carbon export, effectively removes organic carbon from the surface waters and the atmosphere, sequestering it in the deep sea for potentially thousands of years.
Professor Karl’s estimates suggest that the amount of organic carbon exported from this bloom could be equivalent to approximately half of the carbon dioxide initially released by the Kīlauea eruption. "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," he stated. This discovery highlights a significant natural mechanism by which volcanic activity can, indirectly, mitigate atmospheric carbon dioxide levels. The unique alignment of volcanic ash deposition with the naturally nutrient-starved conditions of the study area created a perfect storm for a bloom of this magnitude, one that was readily detectable by both satellite remote sensing and data from pre-deployed Argo floats.
Broader Impact and Future Research
The findings from this study have far-reaching implications for our understanding of ocean-atmosphere interactions, biogeochemical cycles, and the potential impacts of future volcanic events on marine ecosystems. The research team is now poised to expand their monitoring efforts. "The research team is prepared to track future volcanic eruptions and their effects on phytoplankton blooms," the study concludes. Should another major eruption occur, they have plans to deploy a research vessel to study the development and response of any resulting bloom in real-time. This proactive approach will allow for more detailed in-situ measurements and a deeper understanding of the complex processes involved.
The North Pacific Subtropical Gyre is one of the largest and most oligotrophic (nutrient-poor) oceanic regions on Earth. The discovery of such a profound bloom, triggered by a distant terrestrial event, underscores the interconnectedness of Earth’s systems. It suggests that volcanic ash, often perceived primarily as a hazard to aviation and human health, can also act as a vital nutrient source, driving significant biological productivity in remote oceanic areas.
This research also refines our understanding of the ocean’s carbon cycle. The ocean absorbs a significant portion of the atmospheric carbon dioxide produced by human activities. While this natural carbon sequestration process driven by volcanic ash is unlikely to offset anthropogenic carbon emissions entirely, it represents an important component of the global carbon budget that warrants further investigation. By studying these natural fertilization events, scientists can better model and predict the ocean’s response to nutrient inputs, whether natural or anthropogenic. The study serves as a compelling reminder that even events on land can have profound and far-reaching consequences for the health and functioning of our planet’s oceans.