By Lina carolina 
The colossal eruption of Hawaii’s Kīlauea volcano in May 2018, a cataclysmic event that sent an ash plume soaring nearly five miles into the atmosphere, has been definitively linked to an unprecedented phytoplankton bloom in the North Pacific Subtropical Gyre. A groundbreaking study, published recently in JGR Oceans and conducted by an international consortium of researchers, has unveiled a complex biogeochemical chain reaction: volcanic ash, carried by prevailing winds over 1,200 miles, fertilized a vast expanse of the ocean, triggering a rare and exceptionally large summertime bloom of microscopic marine algae. This discovery not only sheds light on the intricate connections between terrestrial geological events and oceanic ecosystems but also offers critical insights into the ocean’s role in the global carbon cycle.
A Cascade of Events: From Volcano to Ocean Bloom
The 2018 Kīlauea eruption was one of the most significant in more than two centuries, characterized by its prolonged effusive phase and the dramatic injection of millions of cubic feet of molten lava into the Pacific Ocean off the Big Island of Hawai’i. Beyond the immediate terrestrial devastation and the release of vast quantities of sulfur dioxide and carbon dioxide into the atmosphere, the eruption’s impact extended far beyond the Hawaiian archipelago. While Kīlauea is renowned for its frequent activity, previous volcanic ash releases had not been demonstrably linked to open-ocean phytoplankton blooms of this magnitude.
The research team’s meticulous analysis, drawing upon satellite imagery, atmospheric data, and oceanographic observations, has pieced together a compelling narrative. Following the explosive phase of the eruption, prevailing atmospheric currents acted as a long-distance courier, transporting fine particles of volcanic ash westward across the Pacific. These ash particles, containing essential trace elements like iron, nitrogen, and phosphorus, acted as a potent fertilizer when they eventually settled onto the nutrient-depleted surface waters of the North Pacific Subtropical Gyre.
Unprecedented Scale and Duration
David Karl, a study co-author 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, emphasized the extraordinary nature of the observed bloom. "The scale and duration of this bloom were both massive, and probably the largest ever reported for the North Pacific," Karl stated. He further elaborated on the significance of the findings: "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 North Pacific Subtropical Gyre, a vast expanse of ocean characterized by oligotrophic (nutrient-poor) conditions, typically supports limited phytoplankton productivity. The sheer size of the 2018 bloom, which stretched across an area estimated to be thousands of square miles and persisted for an extended period, was therefore a striking anomaly. This region, situated approximately 1,200 miles west of Kīlauea, became an unexpected beneficiary of the volcano’s immense power.
Tracing the Ash: Atmospheric Transport and Ocean Deposition
Wee Cheah, the study’s corresponding author and a Senior Lecturer at the Institute of Ocean and Earth Sciences at Universiti Malaya, detailed the sophisticated methods used to track the ash’s journey. "After the 2018 eruption, the prevailing winds transported ash particles to the west," Cheah explained. "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."
The deposition of these ash particles into the ocean is a complex process influenced by several factors. The density, size, and shape of the particulate matter, coupled with prevailing atmospheric conditions such as rainfall, dictate how and when the ash settles out of the atmosphere. In this instance, the persistent atmospheric transport allowed the ash to travel significant distances before eventually falling onto the ocean surface, acting as a slow-release fertilizer.
Satellite Detection and Ocean Color Analysis
The identification of the phytoplankton bloom itself was made possible through advanced remote sensing technologies. Chun Hoe Chow, Associate Professor in the Department of Marine Environmental Informatics at the National Taiwan Ocean University and lead author of the study, along with his co-authors, utilized satellite data to monitor ocean color. Variations in ocean color are a direct indicator of phytoplankton abundance, as chlorophyll pigments within the algae absorb certain wavelengths of light and reflect others, giving the water a greenish hue.
"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. The convergence of atmospheric ash transport and the subsequent oceanic response, all captured by satellite sensors, provided a unique opportunity to study this large-scale phenomenon.
The Role of Iron and Other Nutrients
The key to stimulating such a massive bloom in a nutrient-limited environment lies in the composition of volcanic ash. As Karl elucidated, "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." Iron, in particular, is a critical micronutrient for phytoplankton, playing a vital role in photosynthesis and nitrogen assimilation.
The study also highlights the importance of nitrogen-fixing microbes, a specialized group of phytoplankton that can thrive in nitrogen-poor waters. The availability of iron and other trace elements from the volcanic ash enabled these organisms to flourish, leading to a significant increase in primary productivity.
Implications for the Ocean’s Carbon Cycle
The implications of this massive phytoplankton bloom extend beyond its ecological significance; they have profound consequences for the ocean’s role in regulating atmospheric carbon dioxide. Phytoplankton are the primary producers in marine ecosystems, forming the base of the food web and playing a crucial role in the biological carbon pump.
When these microscopic organisms grow and reproduce, they absorb carbon dioxide from the atmosphere through photosynthesis. Upon their death, a significant portion of this organic matter sinks to the deep ocean. This process, known as carbon export, effectively removes carbon from the upper ocean and atmosphere, sequestering it in the deep sea for potentially thousands of years.
"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 reports.
The researchers estimate that the amount of organic carbon exported from the surface as a result of this bloom could be substantial. "Our estimates are that export of organic carbon may be equivalent to about half of the carbon dioxide initially released from the eruption," Karl stated. This finding suggests that natural processes, such as volcanic ash deposition, can play a significant role in mitigating the greenhouse gas emissions associated with large volcanic events.
"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," Karl added. "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."
A New Frontier in Volcanic Impact Research
The study represents a significant advancement in understanding the far-reaching impacts of volcanic activity. While the immediate effects of eruptions on local environments are well-documented, this research underscores the interconnectedness of Earth’s systems and the capacity for geological events to influence distant ecosystems.
The research team is now poised to leverage this newfound understanding to monitor future volcanic eruptions. The ability to predict and track the potential for ash-induced phytoplankton blooms could become an important tool for scientists studying ocean biogeochemistry and the global carbon cycle. The researchers have expressed their readiness to deploy research vessels to study the development and response of such blooms in real-time should another major eruption occur, promising further invaluable data for this critical area of scientific inquiry. This proactive approach underscores the commitment to refining our understanding of Earth’s dynamic processes and their intricate interplay.