By Lina carolina 
The colossal eruption of Kīlauea Volcano in May 2018, a cataclysmic event that spewed an immense volume of ash into the atmosphere in a plume reaching nearly five miles high, has been definitively linked to a rare and exceptionally large summertime phytoplankton bloom in the North Pacific Subtropical Gyre. This unprecedented oceanic event, occurring in the summer of 2018, was directly triggered by volcanic ash from Kīlauea that journeyed approximately 1,200 miles west of the volcano before settling onto the ocean surface. The groundbreaking findings of this international research collaboration were recently published in the esteemed scientific journal JGR Oceans, offering profound insights into the complex interplay between terrestrial volcanism and marine ecosystems.
An Unprecedented Oceanic Phenomenon
The scale and duration of the observed phytoplankton bloom were truly staggering, likely representing the most significant event of its kind ever documented in the North Pacific. "The scale and duration of this bloom were both massive, and probably the largest ever reported for the North Pacific," stated David Karl, a distinguished co-author of the study and a leading figure in microbial oceanography. Karl, who holds the Victor and Peggy Brandstrom Pavel Professor chair and directs the Center for Microbial Oceanography: Research and Education at the University of Hawai’i (UH) at Mānoa School of Ocean and Earth Science and Technology, emphasized the study’s critical contribution: "Our study shows the connection between the eruption of Kīlauea and bloom formation far from the volcano. This can be used to refine our understanding of phytoplankton bloom dynamics and to improve our understanding of the ocean’s carbon cycle."
While Kīlauea is recognized as one of the world’s most active volcanoes, with a history of multiple eruptions over the past four decades, volcanic ash released from the Hawaiian island had not previously been conclusively connected to widespread open-ocean phytoplankton blooms. The 2018 eruption, however, stood out as one of the most significant in over two centuries. It unleashed millions of cubic feet of molten lava into the surrounding ocean waters off the Big Island of Hawai’i, concurrently releasing an estimated 50 kilotons of sulfur dioxide and approximately 77 kilotons of carbon dioxide into the atmosphere daily. This dual release of materials into both the ocean and atmosphere created a unique set of conditions that scientists are now beginning to fully comprehend.
Tracing the Ash: From Fiery Volcano to Fertile Ocean
Previous research spearheaded by UH Mānoa oceanographers had already identified a localized phenomenon: as lava flowed into the ocean, it significantly warmed the nutrient-rich bottom waters. This warming process rendered the deep waters more buoyant, causing them to rise to the sunlit surface. This influx of nutrients directly stimulated phytoplankton growth, leading to an extensive microbial bloom offshore of Hawai’i Island itself. However, the 2018 eruption’s impact extended far beyond these immediate coastal waters. Volcanic ash, a fine particulate matter, possesses the remarkable ability to be transported vast distances by atmospheric currents, particularly during explosive eruptions that propel materials to extreme altitudes.
"After the 2018 eruption, the prevailing winds transported ash particles to the west," explained Wee Cheah, the study’s corresponding-author and a Senior Lecturer at the Institute of Ocean and Earth Sciences at Universiti Malaya. Cheah elaborated on the tracking mechanisms: "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. 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." This intricate dance between atmospheric circulation and precipitation patterns dictated the eventual deposition of volcanic material across the Pacific.
The research team, led by Chun Hoe Chow, Associate Professor in the Department of Marine Environmental Informatics at the National Taiwan Ocean University, employed a sophisticated suite of tools to piece together the narrative of the bloom. Beyond tracking the atmospheric transport of ash across the Pacific using satellite data that monitored aerosol optical depth, the scientists also analyzed satellite imagery that revealed ocean color. Ocean color is a widely recognized proxy for the presence and abundance of phytoplankton. This analysis unequivocally detected a massive bloom situated near the International Date Line, a region typically characterized by oligotrophic, or nutrient-poor, waters. The team then undertook a comprehensive investigation, correlating these observations with physical oceanographic conditions to elucidate both the precise timing and the unexpected location of this significant surface bloom, a feature that deviates markedly from the norm for this particular oceanic zone.
The Nutritional Catalyst: Iron and Trace Elements in Volcanic Ash
The key to unlocking the mystery of the bloom lay in understanding the elemental composition of the volcanic ash. Open ocean waters, particularly within large gyres like the North Pacific Subtropical Gyre, are notoriously nutrient-depleted. This scarcity of essential nutrients acts as a significant limiting factor for primary productivity. However, volcanic ash is not merely inert dust; it is a complex mixture of minerals, often rich in elements crucial for marine life.
"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," Professor Karl elucidated. Iron, in particular, is a vital micronutrient that often limits phytoplankton growth in vast oceanic regions. Volcanic ash, with its high iron content, acts as a potent fertilizer, providing the necessary building blocks for a significant proliferation of these microscopic marine plants. The presence of other trace elements and even phosphate in the ash further contributes to this fertilizing effect, enabling the growth of specialized phytoplankton communities, including those capable of fixing atmospheric nitrogen, a critical nutrient that is often scarce in these remote ocean environments.
A Natural Carbon Sequestration Event
The explosive growth of these specialized phytoplankton had profound implications for the global carbon cycle. As these microscopic organisms thrived, they converted atmospheric carbon dioxide into organic matter through photosynthesis. Upon their demise, this organic matter sank to the deep ocean, effectively removing a substantial amount of carbon from the surface layer and, by extension, from the atmosphere. This process, known as biological carbon export, is a crucial component of the ocean’s role in regulating atmospheric CO2 levels.
"Our estimates are that export of organic carbon may be equivalent to about half of the carbon dioxide initially released from the eruption," Professor Karl revealed, highlighting the significant carbon sequestration capacity of this natural event. "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." The synergy between the ash-induced nutrient enrichment and the pre-existing nutrient-poor conditions created a perfect storm for a massive, satellite-detectable bloom. The fortuitous deployment of Argo floats, autonomous profiling floats that collect data on ocean temperature, salinity, and other parameters, further corroborated the scale and impact of the bloom.
Broader Implications and Future Research
This study offers a critical piece of the puzzle in understanding the complex and often underestimated influence of volcanic activity on global biogeochemical cycles. The findings underscore the interconnectedness of Earth’s systems, demonstrating how a terrestrial event can have far-reaching impacts on marine ecosystems and atmospheric composition. The research team is now poised to leverage this newfound understanding to enhance our predictive capabilities regarding future volcanic events and their oceanic consequences.
"The research team is prepared to track future volcanic eruptions and their effects on phytoplankton blooms," a spokesperson for the research consortium confirmed. "If another major eruption occurs, they plan to deploy a research vessel to study the bloom’s development and response in real-time." Such future expeditions, equipped with advanced sensors and sampling technologies, will allow for direct observation and detailed analysis of bloom dynamics, providing invaluable data to refine climate models and improve our understanding of the ocean’s capacity to absorb atmospheric carbon dioxide. This proactive approach to scientific inquiry promises to yield even greater insights into the delicate balance of our planet’s interconnected systems. The ability to monitor and potentially predict such large-scale oceanic responses to volcanic events opens new avenues for climate research and could inform strategies for understanding and potentially mitigating the impacts of climate change. The Kīlauea eruption of 2018, while a natural disaster, has inadvertently provided a unique, large-scale laboratory for scientists to study fundamental processes that govern life and carbon cycling in the vast Pacific Ocean.
