By Lina carolina 
The explosive eruption of Kīlauea volcano in May 2018, which sent a plume of ash soaring nearly five miles into the atmosphere, had an unexpected and profound impact on marine ecosystems over 1,200 miles away. A groundbreaking new study, published in the esteemed journal JGR Oceans, reveals that the volcanic fallout from this colossal eruption was the direct catalyst for a rare and exceptionally large summertime phytoplankton bloom in the North Pacific Subtropical Gyre. This discovery offers a critical new perspective on the intricate connections between terrestrial geological events and oceanic biological productivity, with significant implications for understanding global carbon cycles.
The research, spearheaded by an international consortium of scientists, meticulously traced the journey of Kīlauea’s ash across the Pacific. While volcanic activity is a frequent occurrence for Kīlauea, one of the world’s most active volcanoes, this particular eruption in 2018 stood out for its immense scale and the far-reaching consequences of its atmospheric debris. The study highlights how ash particles, laden with essential nutrients, acted as a vital fertilizer for the nutrient-starved waters of the open ocean, triggering a biological response of unprecedented magnitude.
A Cascade of Events: From Eruption to Bloom
The events unfolded with a dramatic display of geological power. In May 2018, Kīlauea unleashed a series of highly energetic eruptions, a period marked by effusive lava flows that dramatically reshaped the landscape of Hawaiʻi Island and explosive events that injected vast quantities of ash and gases into the stratosphere. The eruption was one of the most significant in over two centuries, spewing millions of cubic feet of molten rock into the ocean and releasing an estimated 50 kilotons of sulfur dioxide and approximately 77 kilotons of carbon dioxide into the atmosphere daily.
Previous research had already established a localized connection between Kīlauea’s lava-ocean interaction and phytoplankton growth. As molten lava poured into the Pacific, it heated the surrounding seawater, causing nutrient-rich deep waters to rise to the sunlit surface. This upwelling of essential nutrients stimulated phytoplankton activity offshore of Hawaiʻi Island, creating visible blooms. However, the 2018 eruption’s impact extended far beyond these immediate coastal effects, demonstrating the potent influence of atmospherically transported ash.
The prevailing winds following the eruption acted as a colossal conveyor belt, carrying Kīlauea’s ash westward across the vast expanse of the Pacific Ocean. Scientists utilized advanced satellite technology, specifically Earth-orbiting instruments designed to detect changes in atmospheric optical clarity, to meticulously track the dispersal of these aerosols. These measurements, known as aerosol optical depth, provided crucial data on the density, size, and distribution of the airborne ash particles.
"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," explained Wee Cheah, the study’s corresponding author and a Senior Lecturer at the Institute of Ocean and Earth Sciences at Universiti Malaya. "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."
The North Pacific Subtropical Gyre: A Fertile Ground Awakened
The North Pacific Subtropical Gyre, a vast, clockwise-rotating current system, is typically characterized by oligotrophic conditions – meaning its waters are nutrient-poor and support relatively low levels of biological productivity. This makes the immense bloom observed in the summer of 2018 particularly remarkable.
Chun Hoe Chow, the study’s lead author and an Associate Professor in the Department of Marine Environmental Informatics at the National Taiwan Ocean University, along with his co-authors, employed satellite-based ocean color sensors. These instruments detect the spectral signature of sunlight reflected from the ocean surface, providing an indirect measure of phytoplankton abundance. The data revealed a sprawling bloom stretching across a significant portion of the gyre, located near the International Date Line, an area not typically associated with such intense biological activity during the summer months.
The research team conducted a rigorous analysis, correlating the satellite observations with meteorological data and oceanographic conditions. Their findings unequivocally pointed to the deposition of volcanic ash as the primary driver of this extraordinary bloom.
The Science Behind the Bloom: Nutrient Enrichment and Specialized Microbes
The key to understanding this phenomenon lies in the composition of volcanic ash. While seemingly inert, ash particles are rich in essential minerals that are scarce in the open ocean.
"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," stated David Karl, a study co-author, Victor and Peggy Brandstrom Pavel Professor, and director of the Center for Microbial Oceanography: Research and Education at the University of Hawaiʻi at Mānoa School of Ocean and Earth Science and Technology.
Professor Karl further elaborated on the specific types of organisms that benefited from this nutrient influx. "This is especially true for the so-called nitrogen-fixing microbes that can grow in the absence of additional nitrogen," he added. These specialized microbes possess the remarkable ability to convert atmospheric nitrogen gas into a usable form for biological processes, a capability that is particularly advantageous in nitrogen-limited environments.
The scale and duration of the bloom were unprecedented. "The scale and duration of this bloom were both massive, and probably the largest ever reported for the North Pacific," Professor Karl emphasized. This finding underscores the significant, and often underestimated, role that episodic geological events can play in regulating oceanic ecosystems.
Implications for the Global Carbon Cycle: Carbon Sequestration
The consequences of such a massive phytoplankton bloom extend far beyond the immediate visual spectacle. Phytoplankton form the base of the marine food web and play a crucial role in the global carbon cycle through photosynthesis, absorbing carbon dioxide from the atmosphere and converting it into organic matter.
The tremendous growth of these specialized phytoplankton in the North Pacific Subtropical Gyre resulted in the production of a vast amount of organic matter. When these organisms eventually die, their remains sink to the deep ocean. This process, known as carbon export, effectively sequesters a significant portion of organic carbon from the surface layers of the ocean and, consequently, from the atmosphere.
The study’s estimates are striking: "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. This natural process of marine carbon dioxide sequestration, triggered by volcanic ash deposition, highlights a critical feedback loop in Earth’s climate system.
"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," Professor Karl explained. The unique alignment of volcanic ash deposition with the nutrient-starved conditions of the study area created a perfect storm for bloom formation, a phenomenon readily detectable by advanced remote sensing technologies and autonomous oceanographic instruments like Argo floats.
A New Frontier in Oceanographic Research
This research opens up new avenues for understanding the complex interplay between geological activity and ocean health. It demonstrates that events occurring on land can have profound and far-reaching impacts on distant marine environments, influencing global biogeochemical cycles.
The study’s findings have significant implications for climate modeling and our understanding of the ocean’s capacity to absorb atmospheric carbon dioxide. By quantifying the carbon sequestration potential of ash-induced phytoplankton blooms, scientists can refine predictions about the ocean’s role in mitigating climate change.
Looking ahead, the research team is poised to leverage this groundbreaking discovery for future investigations. "The research team is prepared to track future volcanic eruptions and their effects on phytoplankton blooms," the study concludes. Should another major eruption occur, the scientists plan to deploy a research vessel to conduct real-time observations, allowing for an unprecedentedly detailed study of bloom development and response. This proactive approach promises to further illuminate the dynamic relationship between volcanic activity and the health of our planet’s oceans.
The Kīlauea eruption of 2018 serves as a powerful reminder of the interconnectedness of Earth’s systems. What begins as a dramatic display of geological power on a remote island can, through the intricate mechanisms of atmospheric transport and oceanographic processes, lead to significant biological and biogeochemical transformations on a global scale. This research not only expands our scientific knowledge but also underscores the importance of continued monitoring and research into these complex natural phenomena.
