By Lina carolina 
The colossal eruption of Kīlauea volcano in May 2018, which sent an immense plume of ash nearly five miles into the atmosphere, has been definitively linked to an extraordinary summertime phytoplankton bloom in the North Pacific Subtropical Gyre. This unprecedented event, occurring approximately 1,200 miles west of the Hawaiian volcano, was triggered by volcanic ash particles settling on the ocean surface, according to a groundbreaking study by an international team of researchers. The findings, published recently in the esteemed journal JGR Oceans, shed new light on the intricate connections between terrestrial volcanic activity and remote marine ecosystems, with significant implications for understanding the ocean’s role in the global carbon cycle.
The scale and duration of this phytoplankton bloom were extraordinary, with co-author David Karl, Victor and Peggy Brandstrom Pavel Professor and director of 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, describing it as "probably the largest ever reported for the North Pacific." Karl emphasized the study’s crucial revelation: "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, direct links between its ash emissions and widespread open-ocean phytoplankton blooms had not been previously established. The 2018 eruption, however, was one of the most significant in over two centuries. It not only expelled millions of cubic feet of molten lava into the waters off Hawai’i Island but also released an estimated 50 kilotons of sulfur dioxide and approximately 77 kilotons of carbon dioxide into the atmosphere daily. These figures highlight the sheer magnitude of the volcanic event and its potential to influence atmospheric and oceanic processes on a global scale.
Kīlauea’s Far-Reaching Influence: From Local Waters to the Open Ocean
Previous research, spearheaded by UH Mānoa oceanographers, had already documented localized phytoplankton growth in the vicinity of Kīlauea. As lava entered the ocean, it had the effect of warming nutrient-rich bottom waters, making them more buoyant and consequently rising to the sunlit surface. This upwelling of essential nutrients directly stimulated phytoplankton proliferation, creating a visible microbial plume offshore of Hawai’i Island. However, the 2018 eruption’s impact extended far beyond these localized effects. The explosive nature of the eruption was key, injecting fine ash particles high into the atmosphere, where they could be transported by prevailing winds over vast distances.
Wee Cheah, the study’s corresponding author and Senior Lecturer at the Institute of Ocean and Earth Sciences at Universiti Malaya, explained the atmospheric transport mechanism. "After the 2018 eruption, the prevailing winds transported ash particles to the west," Cheah stated. The trajectories of these ash particles were meticulously tracked by Earth-orbiting satellites that monitor changes in atmospheric clarity, often referred to as aerosol optical depth. The eventual deposition of this ash onto the ocean surface was a complex process, influenced by factors such as the density, size, and shape of the particulate matter, as well as prevailing atmospheric conditions, particularly rainfall, which can facilitate the fallout of ash from the atmosphere.
Satellite Observations Reveal an Unprecedented Marine Phenomenon
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 multifaceted approach to unravel the mystery of the bloom. Beyond tracking the atmospheric transport of ash across the Pacific, they utilized sophisticated satellite data to analyze ocean color. Ocean color is an indirect yet reliable indicator of phytoplankton abundance; a vibrant green hue, for instance, typically signifies a dense concentration of these microscopic marine plants. The satellite imagery unequivocally revealed a massive bloom situated near the international dateline, a region not typically known for such extensive surface algal growth during the summer months.
The scientists conducted a thorough analysis of these observations, integrating them with an investigation into the physical conditions that might explain both the timing and the unusual location of this significant surface bloom. This comprehensive approach allowed them to build a compelling case for the volcanic ash as the primary catalyst.
The Chemical Cocktail That Fueled the Bloom
The open ocean, particularly the North Pacific Subtropical Gyre, is characterized by its nutrient-depleted waters. This oligotrophic environment makes it challenging for phytoplankton to thrive. However, the volcanic ash introduced a critical cocktail of essential nutrients. "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," explained Professor Karl.
Iron is a particularly vital micronutrient for phytoplankton, often limiting their growth in vast oceanic regions. Volcanic ash, derived from the Earth’s crust, is rich in iron and other trace elements that are scarce in the surface waters of the open ocean. The study also pointed to the potential contribution of phosphate, another essential nutrient for marine life. Furthermore, the ash provided a stimulus for specific types of phytoplankton, notably nitrogen-fixing microbes, which possess the remarkable ability to utilize atmospheric nitrogen even in the absence of dissolved nitrogen in the water column, a common limitation in such environments. This specialized group of microbes, often referred to as diazotrophs, can thrive under these unique conditions, leading to explosive growth.
Carbon Sequestration: A Natural Climate Regulation Mechanism
The consequence of such a massive phytoplankton bloom is the production of a substantial quantity of organic matter. As these microscopic organisms complete their life cycles, they die and sink to the deep ocean. This process, known as export production, effectively removes a significant amount of organic carbon from the surface layers of the ocean and, consequently, from the atmosphere. This natural phenomenon plays a crucial role in the ocean’s carbon cycle and its capacity to regulate atmospheric carbon dioxide levels.
Professor Karl estimated that the export of organic carbon resulting from the 2018 Kīlauea-induced bloom may have been equivalent to approximately half of the carbon dioxide initially released by the 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 noted. The confluence of ash deposition and the nutrient-starved conditions in the study area created a perfect storm for an exceptionally large bloom, readily detectable by both satellite remote sensing and autonomous Argo floats previously deployed in the region.
Broader Implications and Future Research
The findings of this study have far-reaching implications, enhancing our understanding of how major geological events on land can exert influence on remote marine ecosystems and, by extension, global climate regulation. The research team is now well-positioned to monitor future volcanic eruptions and assess their potential impacts on phytoplankton dynamics.
The team’s preparedness for future events is noteworthy. They have expressed their intention to deploy a research vessel to study the development and response of any subsequent blooms in real-time, should another major eruption occur. This direct observational approach would provide invaluable data for validating and refining the models used in the current study, offering unprecedented insights into the immediate and ongoing effects of volcanic ash on ocean productivity and biogeochemical cycles.
The ability to quantify the carbon sequestration capacity of such volcanic events offers a unique perspective on natural climate mitigation mechanisms. While volcanic eruptions are often associated with negative environmental impacts, this research highlights a less-discussed consequence: the potential for these events to temporarily enhance the ocean’s capacity to absorb atmospheric carbon dioxide.
This research underscores the interconnectedness of Earth’s systems. The dramatic eruption of Kīlauea, a seemingly localized event, ultimately triggered a cascade of effects that spanned thousands of miles, influencing the very fabric of the North Pacific marine ecosystem and demonstrating the ocean’s vital role in global carbon cycling. As climate science continues to evolve, understanding these complex interactions between terrestrial and marine environments will be paramount in developing comprehensive strategies for climate change mitigation and adaptation. The Kīlauea eruption and the subsequent phytoplankton bloom serve as a powerful reminder of the dynamic and often surprising ways our planet functions.
