By Lina carolina 
The colossal eruption of Hawaiʻi’s Kīlauea Volcano in May 2018, a cataclysmic event that spewed an immense plume of ash nearly five miles into the atmosphere, has revealed a remarkable and far-reaching consequence: a rare and colossal summertime phytoplankton bloom in the North Pacific Subtropical Gyre. A groundbreaking new study, published in the esteemed journal JGR Oceans, details how ash particles, carried by prevailing winds approximately 1,200 miles west of the volcano, acted as a crucial catalyst for this extraordinary oceanic event. This research, a collaborative effort by an international team of scientists, underscores the interconnectedness of terrestrial geological processes and the delicate balance of marine ecosystems, offering profound insights into oceanographic dynamics and the global carbon cycle.
A Bloom of Unprecedented Scale
The North Pacific Subtropical Gyre, a vast expanse of the Pacific Ocean characterized by its oligotrophic (nutrient-poor) waters, is not typically a region known for supporting massive phytoplankton blooms, especially during the summer months. However, the 2018 event defied these expectations, exhibiting a scale and duration that scientists described as "massive" and "probably the largest ever reported for 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 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 (UH) at Mānoa School of Ocean and Earth Science and Technology. Professor Karl’s expertise in microbial oceanography provided critical insights into the biological processes at play. He emphasized the study’s significance in demonstrating a tangible link between a terrestrial volcanic event and a distant oceanic phenomenon. "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."
The Kīlauea Eruption: A Geological and Atmospheric Phenomenon
The 2018 Kīlauea eruption was one of the most significant in over two centuries, dramatically reshaping the landscape of Hawaiʻi Island. The eruption commenced in earnest on May 3, 2018, with a series of explosive events and lava flows that continued for several months. The sheer volume of molten rock entering the ocean off the Big Island was immense, and the atmospheric release of gases was equally substantial. Estimates indicate that the eruption released approximately 50 kilotons per day of sulfur dioxide and about 77 kilotons per day of carbon dioxide into the atmosphere.
While Kīlauea is recognized as one of the world’s most active volcanoes, with multiple eruptions in the preceding four decades, previous research had not established a direct link between its volcanic ash and open ocean phytoplankton blooms. The explosive nature and prolonged duration of the 2018 eruption, however, were key factors in the atmospheric dispersal of volcanic materials.
Tracing the Ash: From Volcano to Ocean
The journey of Kīlauea’s ash from its fiery origin to the distant North Pacific is a testament to the power of atmospheric circulation. Following the eruption, prevailing winds played a crucial role in transporting ash particles westward across the vast Pacific.
"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 in the Institute of Ocean and Earth Sciences at Universiti Malaya. Dr. Cheah highlighted the role of advanced monitoring technologies in tracking this atmospheric transport. "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."
Aerosol optical depth (AOD) is a measure of how much light is scattered or absorbed by aerosols in the atmosphere. Satellites equipped with sensors capable of measuring AOD provided crucial data, allowing researchers to map the extent and movement of the ash plume. The eventual deposition of these fine particles onto the ocean surface was the critical step that initiated the subsequent phytoplankton bloom.
The Nutrient Trigger: Iron and Trace Elements
The open ocean, particularly the North Pacific Subtropical Gyre, is characterized by its low concentration of essential nutrients. This scarcity limits the growth of phytoplankton, the microscopic marine algae that form the base of most ocean food webs and play a vital role in absorbing atmospheric carbon dioxide.
Volcanic ash, however, is rich in minerals, most notably iron. Iron is a crucial micronutrient for phytoplankton growth, particularly for nitrogen-fixing microbes. While nitrogen is often the primary limiting nutrient in many oceanic regions, iron can become the limiting factor in areas like the North Pacific Subtropical Gyre.
"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 elaborated. These nitrogen-fixing microbes are particularly important as they can convert atmospheric nitrogen gas into a form usable by other marine organisms, further fueling the bloom.
A Symphony of Data: Satellite Imagery and Oceanographic Surveys
The research team employed a multi-faceted approach to confirm the connection between the Kīlauea ash and the massive bloom. Beyond tracking the atmospheric transport of ash, lead author Chun Hoe Chow, Associate Professor in the Department of Marine Environmental Informatics at the National Taiwan Ocean University, and his co-authors meticulously analyzed satellite data that monitors ocean color.
Ocean color is an indirect but powerful indicator of phytoplankton abundance. When phytoplankton are present in large numbers, they give the surface waters a distinct greenish hue due to the chlorophyll pigment within them. The satellite data revealed a striking and unusually intense bloom situated near the dateline, a location far removed from the Kīlauea eruption site.
"The team conducted a comprehensive analysis of the observations and investigated physical conditions to explain both the timing and the location of the surface bloom, a feature that is not typical in this region," the study notes. This comprehensive analysis likely involved examining sea surface temperature, ocean currents, and other environmental factors that could have influenced the bloom’s development. The alignment of the ash deposition with the observed bloom was a key piece of evidence.
Furthermore, the study likely integrated data from the Argo float program. Argo floats are autonomous profiling instruments that drift through the world’s oceans, measuring temperature and salinity. Some advanced Argo floats can also measure other parameters, potentially including chlorophyll fluorescence, which can indicate phytoplankton biomass. The presence of these deployed instruments in the region would have provided valuable in-situ data to complement the satellite observations.
Carbon Sequestration: A Natural Climate Regulator
The consequences of this massive phytoplankton bloom extend beyond its visual spectacle. The rapid growth of these microscopic organisms leads to a significant increase in the production of organic matter. When these phytoplankton die, they sink to the deep ocean, a process known as export production. This sinking of organic carbon effectively removes carbon from the upper ocean and atmosphere, acting as a natural form of carbon sequestration.
"The growth of these specialized phytoplankton produced a lot of organic matter. When the organisms die and sink to the deep ocean, a large amount of organic carbon is exported from the surface, essentially removing carbon from the upper ocean and atmosphere," the study explains.
Professor Karl provided a quantitative estimate of this natural carbon sequestration: "Our estimates are that export of organic carbon may be equivalent to about half of the carbon dioxide initially released from the eruption." This is a profound finding, suggesting that natural geological events, like volcanic eruptions, can trigger oceanic processes that partially offset their own atmospheric carbon footprint.
This phenomenon of marine carbon dioxide sequestration is not unique to Kīlauea’s 2018 eruption. The researchers posit that it is a recurring process that likely occurs whenever volcanic eruptions inject ash into the atmosphere and transport 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," Karl added.
Implications for Climate Science and Future Research
The findings of this study have significant implications for our understanding of the ocean’s role in the global carbon cycle and the impact of volcanic activity on marine ecosystems. It highlights the potential for remote volcanic eruptions to influence oceanic productivity and carbon sequestration on a global scale.
This research provides a vital case study for refining models of phytoplankton bloom dynamics. By understanding the specific conditions that trigger such blooms – the type of ash, its mineral composition, atmospheric transport patterns, and prevailing oceanographic conditions – scientists can improve their predictions of future bloom events and their associated carbon sequestration potential.
The international research team is now poised to leverage these insights for future endeavors. "The research team is prepared to track future volcanic eruptions and their effects on phytoplankton blooms," the study concludes. "If another major eruption occurs, they plan to deploy a research vessel to study the bloom’s development and response in real-time." Such real-time studies would offer unprecedented opportunities to gather detailed, on-site data, further illuminating the complex interplay between volcanism, atmospheric science, and marine biogeochemistry. This proactive approach underscores a commitment to advancing scientific knowledge and monitoring the Earth’s dynamic systems.
