By Lina carolina 
The colossal eruption of Hawaiʻi’s Kīlauea volcano in May 2018, which unleashed an immense plume of ash nearly five miles high into the atmosphere, played a pivotal role in triggering an exceptionally large and rare summertime phytoplankton bloom in the North Pacific Subtropical Gyre. This unprecedented oceanic event, occurring approximately 1,200 miles west of the volcano, was directly linked to the deposition of volcanic ash on the ocean’s surface, according to a groundbreaking new study published recently in the esteemed journal JGR Oceans. An international consortium of researchers meticulously pieced together satellite imagery, atmospheric data, and oceanographic observations to establish this significant and geographically expansive connection between terrestrial volcanism and marine ecosystems.
The findings of this study are particularly noteworthy given the sheer scale and duration of the observed bloom. "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 and a distinguished professor at the University of Hawaiʻi (UH) at Mānoa’s School of Ocean and Earth Science and Technology. Professor Karl, who holds the Victor and Peggy Brandstrom Pavel Professorship and directs the Center for Microbial Oceanography: Research and Education, emphasized the study’s contribution to understanding oceanic processes. "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 has been one of the world’s most active volcanoes, consistently exhibiting multiple eruptions over the past four decades, the direct link between its ashfall and widespread open-ocean phytoplankton blooms had not been previously established. The 2018 eruption, however, was an event of exceptional magnitude, ranking among the most significant in over two centuries. This cataclysmic event not only expelled millions of cubic feet of molten lava into the surrounding ocean waters off the Big Island of Hawaiʻi but also released an estimated 50 kilotons of sulfur dioxide and approximately 77 kilotons of carbon dioxide into the atmosphere daily. These substantial atmospheric emissions set the stage for far-reaching environmental consequences.
Kīlauea’s Far-Reaching Influence: From Local Waters to Global Atmospheres
Previous research, spearheaded by oceanographers from UH Mānoa, had already illuminated the immediate impact of Kīlauea’s lava-ocean interaction. As incandescent lava flowed into the Pacific, it significantly warmed the underlying nutrient-rich bottom waters. This thermal input rendered the deeper waters more buoyant, facilitating their ascent to the sunlit surface layers. This upwelling of vital nutrients spurred localized phytoplankton growth, creating a visible and extensive microbial plume offshore of Hawaiʻi Island. However, the 2018 eruption’s explosive nature facilitated the transport of volcanic ash to much greater distances, carried aloft by powerful winds and injected high into the atmosphere, a phenomenon critical to the subsequent oceanic bloom.
"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 methods used to track this atmospheric dispersal: "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."
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 array of analytical tools. In addition to meticulously tracking the atmospheric transport of ash across the vast expanse of the Pacific Ocean, they leveraged satellite data to monitor ocean color. This spectral information serves as an indirect but highly effective indicator of phytoplankton presence and abundance. The satellite imagery revealed a dramatic and extensive bloom in the vicinity of the international dateline, a region not typically characterized by such intense biological activity during the summer months. The team’s comprehensive analysis involved scrutinizing these observations in conjunction with physical oceanographic conditions to elucidate the precise timing and geographical locus of this anomalous surface bloom.
The Nutrient Paradox: Volcanic Ash as a Catalyst for Oceanic Life
The open ocean, particularly within gyres like the North Pacific Subtropical Gyre, is characteristically nutrient-depleted. This oligotrophic environment presents a significant limitation to primary productivity. However, the deposition of volcanic ash introduces a crucial supply of essential micronutrients, most notably iron. "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," Professor Karl elucidated. He further highlighted the specific role of certain microbial communities: "especially the so-called nitrogen-fixing microbes that can growth in the absence of additional nitrogen." These specialized phytoplankton, capable of utilizing atmospheric nitrogen, are particularly well-suited to thrive in nutrient-scarce environments when provided with essential trace elements like iron.
The timing of the ashfall was critical. The Kīlauea eruption commenced in early May 2018, with sustained effusive and explosive activity throughout the summer. The prevailing trade winds then carried the ash westward. Satellite observations of aerosol optical depth confirmed significant ash plumes moving across the Pacific during May and June. By July and August, when oceanographic satellite data began to show the burgeoning bloom, the ash had effectively settled onto the ocean surface in the North Pacific Subtropical Gyre, providing the necessary iron and other trace nutrients to trigger a biological cascade.
Carbon Sequestration: A Natural Climate Regulator
The proliferation of these specialized phytoplankton resulted in a substantial increase in the production of organic matter. A significant portion of this newly generated organic carbon was then exported from the surface ocean. When these microscopic organisms complete their life cycles, they sink to the deep ocean, effectively removing carbon from the upper ocean layers and, consequently, from the atmosphere. This process, known as biological carbon sequestration, plays a vital role in regulating Earth’s climate.
"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 stated, underscoring the profound impact of this natural phenomenon. "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 study highlights that this phenomenon is not unique to Kīlauea but is likely a recurring, albeit often unobserved, process. Major volcanic eruptions that inject significant amounts of ash into the stratosphere and are subsequently transported over nutrient-poor oceanic regions could trigger similar, large-scale phytoplankton blooms, leading to substantial carbon sequestration. The magnitude of the 2018 bloom suggests that such events can represent a significant, albeit transient, counterbalance to volcanic carbon emissions.
Future Monitoring and Broader Implications
The research team is keenly aware of the potential for future volcanic activity to influence marine ecosystems and the global carbon cycle. They are actively preparing to monitor subsequent volcanic eruptions and assess their impact on phytoplankton blooms. "If another major eruption occurs, they plan to deploy a research vessel to study the bloom’s development and response in real-time," the study indicates, signifying a commitment to gaining more granular, in-situ data. Such future expeditions would allow for direct sampling of the bloom, detailed analysis of phytoplankton species composition, nutrient cycling, and a more precise quantification of carbon export.
The implications of this research extend beyond understanding the immediate consequences of volcanic eruptions. It underscores the intricate connectivity between Earth’s geological processes and its biological systems. Furthermore, it provides valuable insights into the complex dynamics of the ocean’s carbon cycle, a critical component of global climate regulation. As climate scientists strive to refine their models of carbon sequestration and ocean productivity, understanding the role of episodic, large-scale events like volcanic ash-induced phytoplankton blooms becomes increasingly important. This study offers a compelling case study of how seemingly distant terrestrial events can have profound and far-reaching impacts on the health and functioning of our planet’s oceans, and by extension, its climate. The precise measurement of aerosol optical depth and ocean color through advanced satellite technology has proven instrumental in unveiling these previously hidden connections, paving the way for more comprehensive monitoring and analysis of Earth’s interconnected systems.
