BY MAEVE BRADY ’20
The Kilauea volcano in Hawaii erupted last summer, pouring molten lava into the surrounding ocean during the months of June, July and August. The addition of millions of cubic meters of lava to the water unexpectedly resulted in an explosive growth in the population levels of phytoplankton. This event left scientists scrambling for answers as to how such an explosion of life could occur, especially because that area of the Pacific Ocean is typically nutrient-deficient and therefore a poor environment for phytoplankton growth.
Graphic by Sabrina Edwards ‘20
Phytoplankton are microscopic water-dwellers that contain chlorophyll and photosynthesize. Like land plants, they rely on nutrients such as nitrate to produce energy.
A bloom of phytoplankton occurs when there is an abundance of sunlight and nutrients. It is defined by a rapid increase in the phytoplankton population, to the point that it changes the color of the water it inhabits. Consequently, it is unlikely in such a nutrient-poor area of the ocean as the waters off the coast of the Big Island of Hawaii.
Phytoplankton blooms adjacent to volcanic eruptions are not unheard of. However, this event was a unique opportunity for researchers to study a bloom in nitrate-deficient waters.
Why, then, would an injection of scalding hot lava, which creates plumes of acidic smoke when it enters the water and contains very little in the way of life-supporting nitrate, result in such a startling boom in phytoplankton life? In the end, it wasn’t the nutrients — or lack thereof — that the lava contained, but rather, its boiling temperatures. As the lava spilled into the ocean, it heated the deeper waters, which are far richer in nitrate, and allowed them to bubble to the upper levels. With the addition of nutrients to the sunlit surface waters, the phytoplankton had everything they needed for a biological bloom so large that the billowing green swirls produced by their high concentrations of chlorophyll could be tracked via satellite.
Phytoplankton are vital to the planet’s health; they account for over half the photosynthesis on Earth and produce over half the oxygen that allows land organisms to breathe. They also form a foundational part of the aquatic food chain: phytoplankton are consumed by zooplankton and krill, which are in turn eaten by larger plankton, small fish, penguins and so on, continuing through the marine food web.
All ocean life depends on these tiny organisms that bloomed by the billions in the wake of the Kilauea eruption.
Phytoplankton are crucial to our ecosystem, but climate change is impacting them negatively. The crucial process of mixing surface and deep waters is changing as the oceans warm. Warmer temperatures on the upper layers means less mixing between those sunny surface waters and the deeper, nitrate-rich, colder waters, which in turn means fewer nutrients available for the surface-dwelling phytoplankton.
Volcanic eruptions help by heating the deep layers of the ocean and providing the nitrate banquet that phytoplankton need to bloom, as discussed in the study published in Science Magazine on Sept. 6.
Kilauea’s eruption and other events like it allows life to flourish even in the most inhospitable of conditions.
Last summer, with a counterintuitive combination of nutrient-deprived surface water and scalding, destructive lava, life off the coast of Hawaii bloomed by the billions.